Frequently Asked Question-22
http://www.kiwipumps.com/kiwicms/articles/167/1/Frequently-Asked-Question-22/Page1.html
Jayesh Patel
By Jayesh Patel
Published on 02/2/2010
Tech Quest
Residual Life of Pumps
Q. Our plant is one of the largest LPG unit in the country. most of the pumps are 20yrs old. The fluid handled by different pumps varies from c2-c3, lpg, crude oil, utility water, effluent water etc; can you suggest evaluation methods for fitness for service, analytical & practical method for residual life of pumps for replacement; present operating parameters(mech. & elect) and condition seems o.k based on condition monitoring observation. can you suggest some web sites or books for residual life analysis of process plant dynamic equipment?
Any pump has distinct zones, the wetted zone, the shaft-sealing zone, the bearing arrangement, the coupling and drive. In the wetted zone the pump casing is a pressure vessel and the residual life will be related to the wall-thickness. Pumps handling corrosive and abrasive fluids will have fast thinning of the all-thickness. The important component in the wetted zone is the impeller and the clearances at wearing rings. Wearing rings are of course replaceable parts and clearances can be redeemed to "like new" condition. Cavitation, erosion and corrosion are three major items that will be eating into the life of the impeller. Shaft-sealing zone is always attended to, whenever the leakage exceeds permissible and residual life gets revived with every refurbishment. Bearing life for journal bearings is theoretically infinite, because journal bearings a film of lubricant is supposed to be maintained all through the working of the bearing. If that is provided, there should be no wear and hence infinite life. For anti-friction bearings, the pump-designer selects the bearings, considering the axial and radial loads and desired bearing life, applying also the recommended factors for severity of service. Condition-based maintenance should be giving good indication of the condition of bearings. Most of the components of the "rotating assembly" are replacement spares. All replacements would redeem the residual life to "like new" condition. If so, scope for residual life analysis brings focus primarily to the pump casing, which should be looked at as a pressure vessel, where wall thickness becomes the guiding parameter.
Dosing Pumps & Gland Packing
Q. What are different types of Gland Packing? How does one determine their use? Under what conditions does one use Teflon and Asbestos Gland Packing? We have four Multiflo(V K Pumps) PR-10 Model Pumps that are used for dosing Chemicals in HRSG. Two Pumps serve as LP Dosing pump discharging Hydrazine+water solution at a Pressure of 4kg/cm2. The other two pumps are used as HP Dosing pump discharging Trisodium Phosphate solution at a pressure of 42 kg/cm2. Can we interchange these pumps? Can a LP Dosing Pump now discharging 4 kg/cm2 discharge at 42 kg/cm2 since both the pumps are of same models?
Usually the design of the 'liquid end' of reciprocating piston pumps is related to flow-rate, (volume per stroke multiplied by number of rokes per minute). Volume per stroke is cross-sectional area of piston multiplied by length of stroke. Mostly in a given model of pump, these parameters would be same. If so, one should be able to interchange pumps from one duty to another, provided the flow-rate is same. Pressure would influence the wall-thickness, especially of the cylinder. If that also is same, one can interchange more confidently.
Various types of Pumps & Applications
Q. Can you Please provide me the details of the following :-
1) Definition & Details of Operations of Centrifugal Pump - Also Industrial Applications
2) Details of Operations of Rotary & reciprocating pumps - Also Industrial Applications
3) Operations Details of Parallel & Series operations - Applications and Purpose.
4) Types of Vertical pumps and its operations
5) What the Difference between a Centrifugal Pump & Reciprocating Pump
A complete and comprehensive answer to the question amounts to writing a wholesome book on pumps, because the question asks for definitions and details for centrifugal, rotary and reciprocating pumps, vertical pumps and for applications including industrial. I think some commonplace examples will explain the three basic classes of pumps. The pump used to inflate the tyre-tube of a bicycle is a reciprocating pump. A to-and-fro motion is a reciprocating motion and all pumps where reciprocating motion is employed to do pumping action are reciprocating pumps. Swelling and shrinking motion of our heart t inhaling and exhaling is a motion similar to a reciprocating motion and we have diaphragm pumps working similar to our heart. Diaphragm pumps are also a type of reciprocating pump. The mini monobloc pumps used in many households are centrifugal pumps. Centrifugal pumps are very very commonplace and can be found everywhere, on the dug wells of farmers, in multi-storey residential premises for raising water from ground level reservoir to the overhead tank, etc. Pumps at petrol pumps for filling petrol or diesel in vehicles are most commonly rotary pumps, technically called as rotary positive displacement pumps.
Q. What are canned pumps?
The word "Canned" gets associated with pumps in two contexts - one, in respect of "Canned Motor Pumps" and another in respect of pumps handling volatile liquids like LPG, where a vertical pump has a can around it, deep enough to provide the NPSHr of the pump by virtue of the suction impeller getting as much positive head.
Q. Wanted some information on Osmotic / Osmatic Pumps.
From the name of your company you seem to be involved with water treatment. Reverse Osmosis is a process for purification of water by forcing the raw water through osmotic membrane. Osmosis is a natural phenomenon, by which thinner liquid will travel towards a thicker liquid, even if the two liquids are separated by a permeable membrane. But, for purification, raw water, which is thicker, has to travel across the membrane. This is contrary to natural phenomenon of osmosis. Hence the raw water is required to be forced. And the process is called Reverse Osmosis (RO). The pressure required is quite high, depending upon the content of impurities. RO is supposed to be the process capable of giving purest water, not allowing even micro-organisms to pass through. Because of high pressures, RO was not considered feasible for domestic usage. So, domestic water purification systems were based at best on purification with Ultraviolet rays. However over the last 6 to 8 years domestic RO systems are also available. RO systems have been used on ocean-going vessels since many years. Removal of salinity from sea water to make it potable is again most reliably achieved with RO. Pumps for RO system are in the entire range of sizes from those for domestic systems to even municipal water supply systems.
Axial Float
Q. How to calculate axial float in boilerfeed water multistage pumps.(with and without balancing disc) please enlighten me with diagrams.
Axial float is caused by the axial thrust. There is axial thrust even in single stage pumps. It gets multiplied and hence becomes more pronounced in multistage pumps. Basically axial thrust is caused by a differential pressure across an area. In a closed impeller area of the backshroud between the hub dia and eye diameter experiences suction pressure on one side and impeller's discharge pressure on the other side. This would cause the rotating assembly to be thrust forward towards the suction. In case of semi-open impellers, there is a pressure gradient all the way from the outside diameter of the impeller to the hub diameter. In case of vertical pumps, the total weight of the rotating assembly would also add to the axial thrust. Calculation of axial float will then be related to by what amount the axial thrust would displace the rotating assembly. In most designs the displacement will be arrested by the bearing clearance. Even commonplace deep groove ball bearings are also available in reduced or controlled clearance version and are used in pumps with semi-open impellers. Axial thrust apart from being a regular aspect of a running pump, it becomes a transient phenomenon during starting and stopping of pumps and would cause an impact onto the feature arresting the displacement, viz. bearing clearance or seating face of balancing disc. Balancing disc employs the same basic concept of axial thrust, it being caused by differential pressure over an area, but in the reverse direction. An extempore thought comes to mind that designers can try reducing wear due to transient impacts during starting and stopping, especially during stopping by providing a tapping from beyond the non-return valve to the balancing disc. This may be possible even in existing pumps. Most pumps with balancing-disc are with journal bearings. Hence the balancing disc only serves as the displacement arresting feature. It is susceptible to wear. Hence all balancing disc have a raised portion ring near the outside diameter of the disc. The maximum wear allowance is the height of the raised portion. This is marked on the shaft for easy monitoring by the user for the wear on the balancing disc. Since balancing disc operates with the principle of differential pressure over an area, it is important to ensure the pressure differential. The parallel faces between the balancing disc act as an orifice and cause the differential pressure. So the moving face needs to be set to give minimum clearance, but not so minimum as to cause rubbing. Secondly the throttled pressure has to be tapped off. Otherwise the balancing disc area will just become a pressure vessel and the pressure will balance and there will be no differential pressure to balance the axial thrust. So the line tapping off the throttled pressure should not get clogged. Wear from the balancing disc is itself liable to cause clogging.
Selection of Pump for Agriculture Application
Q. I noticed your detailed question and answers in the magazine from that I am willing to clear my doubts I am a farmer, farming about 60 acre with coconut and sapota groves. I am having part of the land near by a river and a part of the land too far. for that I planned to pass water by underground pipe line, the distance is 2 km approx. with a maximum head of 37 feet discharge height, suction head may be around 15 feet height. I planned to use the underground pipe water by dumping
the local wells before irrigation. for that, 1.What type of pump is needed.
2. How much capacity is needed.
3. Power consumption
4. I planned to use PVC/HDPE in underground (which one is better), GI in open area.
5. Give the pipe dimension throughout the distance Suppose: If I directly irrigate by using drip irrigation (the line provided for drip irrigation is 3" for the whole land)
1. What type of pump is needed
2. Capacity,- power?
3. Pipe material of construction?
4. Give the dimension of pipe throughout the distance
5. Kindly mention the number of air vent valves to be provided.
You have mentioned that you find my answers 'detailed'. Your question has prompted really the 'most detailed' answer! Your question gave me the opportunity of bringing out also the cost, which the nation bears for providing power to agriculture. Thank you hence for your question. It is true that over the last 50 years our country has become self-sufficient in food. The nation is indebted to the farming community for that. But the nation has also borne very heavy cost for providing the power. And it has not been used any intelligently or efficiently by the farming community. There is rampant dishonesty, what with stealing of power! The power supply system cannot manage the quality of power against so much of stealing. And we grumble of very low voltages, fluctuations and trippings. Pump manufacturers end up designing pumps and motors to withstand these vagaries of power, hence that much costlier motors and as much inefficient motors. All these hidden costs finally usurp the pockets of the entire population of the country. Hope, you would find the appropriate methodology for making the right selection of pump. But you may have to do all the calculations all over, especially wherever the assumptions are not correct.
For a ready reference, the assumptions made are as follows.
1) Water requirement for coconut is assumed as 100 mm every fifteen days.
2) Water requirement for drip irrigation is assumed at one-fourth of the above.
3) Frictional head for GI pipe only is taken for illustration. You may check for other pipes, especially HDPE.
4) Other frictional heads for losses in foot valve, non-return valve, bends, etc. are not taken into account.
5) The illustration considers only pumping river water to local wells. Another pump will be required for pumping from local well to the field.
6) Assumption also is made to run the pump for eight hours per day.
7) Percolation in local well(s) or yield of local well is assumed to be 5 liters per second.
8) Total length for pipeline considered is 2 km.
All this procedure of selecting an agricultural pump and composing the system is also covered in Indian Standards IS-9694 Part 1 and IS-10804. Of these IS-10804 also gives ready data about frictional heads for different types of pipes.
For selecting a pump one has to first find out the required discharge and head. Discharge is a rate and not a total quantity. Suppose your 60 acres of land should be fed with 4 inches (100 mm) of water in one irrigation cycle, to find total quantity of water, which will have to be pumped, we would first get all data in proper units.
60 acres = 60*4840 sq. yards = 60*4840*9 sq. ft = 60*4840*9/3.28/3.28 sq. m. Then4 inches (100 mm) of water over this much area means 60*4840*9/3.28/3.28 *0.1 = 24293.6 cubic meters of water. Now you would not be able to irrigate all the 60 acres of land in one day. If you would irrigate say 4 acres per day, so that every acre would get water once in every 15 days, then 4 acres of land would need 24293.6/15 = 1620 cubic meters of water. This will vary. If every acre should get water once in every 10 days, 6 acres will have to be irrigated everyday. Then water to be pumped every day would be 2430 cubic meters. Again I just assumed water requirement as 4 inches in one irrigation cycle. It would be different for different crops and would be different for different methods of irrigation. In drip irrigation, the water requirement could be only one-fourth of that for furrow irrigation. You are planning for coconut and sapota. Now if sapota is to be a crop by inter-cultivation, it would not need separate feed of water. It would share from what is fed to coconut. You will have to check whether this assumption would be correct in drip irrigation, because, in drip irrigation, one feeds water to the root of one plant. So, if coconut takes all the water that is fed at its root, it would not leave any water for sapota. However, it is not practical to lay drip tubing to the root of every sapota plant. Maybe you may feed some extra water to coconut. The irrigation cycle itself would be different in different seasons. For example during summer the interval would have to be water every week, whereas in winter it could be water every three weeks. For pumping requirement one should consider the shortest cycle or interval. I do not have data about requirement of water for coconut. I assumed 4 inches every fifteen days to illustrate the method of calculation. To proceed with calculation, for feeding 1620 cubic meters per day, by running the pump for 8 hours every day, the flow-rate required of the pump would be 1620/8 = 202.5 cubic meters per hour = 2700 liters per minute = 45 liters per second. If drip irrigation would need only one-fourth, it would be 11.25 liters per second. It is logical to use drip irrigation for coconut, because once planted, coconut would grow for years unending. With most other crops like jowar, rice, wheat, sugarcane, etc., the field has to be ploughed and tilled every season. Drip tubing would also get uprooted and will have to be re-laid. This would be a problem even with sprinkler irrigation. This, I guess is the reason, why drip or sprinkler irrigation does not become feasible for many crops, though requirement of water is very economical for these methods of irrigation.
Please note that all the calculation is done assuming all 60 acres being at one place. But it is not so, as you have mentioned. It would be better to do separate calculation for the peice of land near the river and for the one 2 km away. Actually you plan to put water from the river into the wells in the field away from the river. Those wells will have some yield or rate of percolation of their own. If the total yield of the wells is 5 liters per second, then for drip irrigation you would need pumping only 6.25 liters from the river, even if all 60 acres are away from the river.
Anyway, having illustrated calculation to find the discharge for the pump, on to finding the head. You have mentioned maximum 37 feet height above the land near the river and 15 feet depth for drawing water from the river. That makes total height 52 feet = 15.85, say 16 meters. If 6.25 liters per second are to be pumped across 2 km distance, assuming farthest well is at 2 km, the frictional head in a 2.5 inch GI pipe would be 5.7 meters for every 100 meters, so for 2 km, total 114 meters. Instead if one would use 3" pipe it would be only 2.1 meters for every 100 meters, hence 42 meters and for 4" pipe at 0.7 meters for every 100 meters only 14 meters. Adding the frictional head to the height of lifting, 16 meters, the total head for the pump would be 130 meters for 2.5" pipe, 56 meters for 3" pipe and only 30 meters for 4" pipe.
You have also enquired about the type of pipe to be used, whether GI, PVC or HDPE? The issues involved are durability of the pipe, smoothness of the pipe, size or actual inside diameter of pipe and cost of pipe. In case of PVC or HDPE pipes, actual inside diameter is more important than just the size of pipe. Both PVC and HDPE pipes will be smoother than GI, but will have smaller actual inside diameter. Smoothness reduces the frictional head, but less inside diameter increases the frictional head. You would have noticed above that for 3" inside diameter the frictional head is only 2.1 meters for every 100 meters, but increases to 5.7 meters for every 100 meters for 2.5" inside diameter. In respect of durability, PVC is least durable, especially if it is exposed to ultra-violet rays from the sun. There is also the menace of the rats and rodents and you have to protect 2 km long pipe from them. For putting the pipe underground you would have to dig a trench. All that labour would not be needed for taying over-ground. From connsiderations of durability, safety and maintainability, cost of installation including cost of making trench, GI pipe may still be an option to keep in mind.
Coming to motor HP, to pump 6.25 liters per second against 56 meters total head for 3" GI pipe, assuming pump efficiency of 50 percent, one would need 6.25*56/75/0.5 = 9.3 HP, say 10 HP. Pump for same 6.25 liters per second but against total head of 130 meters for 2.5" pipe is likely to be less efficient say pump-efficiency of only 40%. Then motor HP will be 6.25*130/75/0.4 = 27.03 HP, say 30 HP. In fact if you can put pumps in series, at some distance, say at every 600 meters along the pipeline, with 3" pipe the head per pump can be only 19m. Each pump can be more efficient, say, 60%, then motor HP of each pump would be 6.25*19/75/0.6=2.64, say 3 HP. So, one can manage the situation with 3 pumps of only 3 HP each than one pump of 10 HP. And you will appreciate that 3 HP pumps are more commonly available, better mass-produced and hence more competitively priced than one 10 HP pump. Getting spares and repairing and maintenance of 3 HP pumps will be cheaper and more easily manageable than for 10 HP pump. With 4" pipe, requiring total head of only 30 meters, the motor HP required assuming only 50% efficiency would be 6.25*30/75/0.5 = 5 HP. Well, only one 5 HP pump, but 2 km of 4" pipe!
Now there is also the cost of power. Even if this may not be a significant cost to a farmer, the nation bears the cost, say, some Rs. 2 per unit of power, as the cost of generating the power and transmitting it to the ultimate user. For irrigating coconut you will run the pump for 9 months of the year, leaving out 3 months of monsoon. This means using the power at 8 hours per day, for 270 days i.e. for 2160 hours per year. If efficiencies of 3 HP (2.2 kW), 5 HP (3.7 kW) and 10 HP (7.5 kW) motors are taken as 80%, 85% and 90% respectively, for three, one and one number of 3, 5 and 10 HP pumps respectively, the energy consumed comes out to 3*2.2/0.8*2760 = 22,770 units for 3 Nos. 3 HP pumps, 3.7/0.85*2760 = 12014 units for one, 5 HP pump and 7.5/0.9/*2760 = 23000 units. So ANNUAL cost to the nation is Rs. 45540, Rs. 24028 and Rs. 46000 respectively. If the coconut field will be bearing fruit for 45 years after initial gestation of 5 years, irrigating the field for 50 years would cost the nation Rs. 11.385 lakhs, Rs. 6 lakhs and Rs. 11.5 lakhs respectively. The discussion above has brought forth different cost involved, cost of pump, cost of pipe, cost of laying the pipe, periodic cost of spares, repairs and maintenance and the cost of power. Even if a farmer would want to leave out the cost of power, the total of other costs calculated over an average period of 15 years, it would be a good idea to work out the Life Cycle Cost for different options and then make the most economical decision.
Q. What factors will get affected if pipe size of 50mm suction & delivery is used for a pump having flange sizes 100mm by 100mm. Will it harm the pump in any way or will only the discharge get affected?
Frictional loss in 50 mm pipe will be 32 times higher than that in 100 mm pipe! This is wastage of energy. Cost of installation will be cheaper with 50mm pipe. But wastage of energy will happen for the life of the system. Also, if a pump is pumping with a suction lift of, say 6m, and ence effective pipe length of say, 8m and required flow-rate is 6 1/s, the friction loss in 50mm pipe will be 1.5m as against only 0.05m for 100 mm pipe. With further losses in strainer and footvalve and bend and eccentric reducer, etc. the pump may suffer cavitation.
FIELD PROBLEMS
Q. We are regular reader of your Pump magazine. We are encouraged to see your response for different problems related to pumps faced in industries and suggestions sought from you. We are referring one of our specific pump related problem. We will like to have your comments on it. We have a multi stage steam condensate pump in our Urea plant which takes suction from tank at atmospheric pressure and discharges it at 45 Kg/CM2. This pressurised condensate is used at different locations in the plant for different purposes . Now due to some change in process conditions we require condensate pressure up to 32 kg/cm2 only. As pump is discharging at 45 kg/cm2 it is unnecessary loss of electrical energy. We are thinking to remove 2 or 3 impellers to reduce the discharge pressure.
Please tell us whether this is possible or not? What other problems we may face?
What is the general formulae to get the relation between number of stages and pressure delivered a pump?
Pump details are as follows:
Stages : 8 Impeller dia - 180 mm (same for all) Impellers are in series Balance drum provided at discharge end with a balance line d/s of this drum to suction line, Speed: 3000 rpm Intermediate bearing sleeve provided. Capacity : 20 m3/Hr
General relationship between pressure and number of stages is of direct proportion. You have 8 stages for 45 bar. Hence number of stages for 32 bar = 32*8/45=5.69 say 6. So, you can remove 2 stages! With 6 stages you would get 6/8*45=33.75 bar pressure. Power saving will also be in direct proportion. Assuming 60% pump efficiency, at 45 bar pressure and 20 m3/h the input power to pump is 20*45*10.336/270/0.6=57.25 HP. If you have a 75 HP motor, presently it is loaded to 76 oad. At 34 bar for 20 m3/h with same 60% efficiency, the loading of the motor will be 20*34*10.336/270/0.6=43.4 HP only 57.8%. Efficiency of 75 HP motor at such part load operation will be less. To get full benefit of reducing number of stages, you may use a 50 HP motor. You may check whether pump efficiency given in pump characteristics from manufacturer is 60% and accordingly whether using 50 HP motor will be appropriate. Actually manufacturer might have given you pump characteristics with different number of stages also.
Q. The axial flow pump of capacity 7700m3/hr it installed in CLOSED LOOP system under 100 mbar abs vacuum in our plant. When pump was first trial run we observed severe cracking sound in the pump and thought for the possible cavitation due to starvation of pump. The pump was than stopped, acid drained, and on inspection some rubber pieces were found at pump discharge end. Thus, it was thought that these rubber piece were probably causing the abnormal sound. After having carried out the rubber repair of the vessel the pump was re-started Before starting the pump we ensured that the liquid level is up to the desired operating level and Initially the sound was low and intermittent but when vacuum was pulled up to 100 mbar abs. the sound increased abnormally and became continuous. Pump was stopped immediately we took second trial run but, the observations are same i.e., heavy cracking & metallic sound in the pump. We have now stopped the pump. We feel there is some design problem with the pump & its application.(NPSH ?)
Axial flow pumps are essentially high specific speed pumps. And high specific speed pumps would have high NPSHr. No designer can design an axial flow pump with low NPSHr. Vacuum at suction is only making the matter worse. Heavy crackling metallic sound is typical of a pump suffering from cavitation. Since there cannot be a design with low NPSHr, only option is to explore how NPSH available can be improved, so as to have positive margin over NPSHr. Options to be explored seem to be as follows.
1) Whether suction vessel can be at higher elevation above the pump.
2) Whether pump can be lowered to a level below the suction vessel
3) If there is a throttling valve at suction to adjust vacuum at suction, whether the valve can be eliminated or whether the friction loss across the valve can be reduced by using a ball valve and preferably of higher size.
4) Whether the piping on the suction side with all appurtenances like bends, tees, valves can be of higher size
5) Whether vacuum can be less stringent
6) If liquid being handled is at temperature higher than ambient, whether a heat exchanger can be added to cool the liquid to bring down the temperature. Since the pump is in a closed loop, rise in temperature of the liquid circulating in a closed loop is a natural phenomenon. Your observation that the pump starts off okay but noise aggravates after some running is indicative of rise in temperature causing vapour pressure of the liquid going up, thereby promoting cavitation. A heat exchanger to cool the liquid before it gets back into the suction vessel should then help.
Q. In our system we require chilled water at 1000lit/hr and 40-60psig pressure at 7.0deg centigrade. Original pump was centrifugal type with open type straight vane impeller, 2900rpm, single stage pump Due to some reason we had to relocate the pump and chiller and piping length was increased by 30mtr but elevation of pipe was same but when we opened the pump for inspection we found its impeller vane(03 nos) got broken also impeller to casing clearance was 2.0mm so we changed the impeller with new one and dia of new impeller was 1.0mm higher then old one but during functioning pump discharge pressure has dropped to 45psig and flow rate 350lit/hr also rubbing marks were found on impeller vanes so we increased the impeller to suction casing clearance by 0.5mm and pump flow has increased to 450 lit/hr but pressure further dropped to 25psig due to which we can't get the cooling system working properly we also shifted the pump near to system by increasing its suction line and reducing its discharge line since suction water tank of chiller is at higher level then pump center line but condition is same kindly tell me the correct method to increase the discharge pressure and flow of the pump.
For the small discharge and relatively high pressure, the pump ought to be a regenerative turbine type centrifugal pump (IS-8472). You have also mentioned straight vanes, which is typical of these pumps. The performance of these pumps is very sensitive to clearance between casing and impeller. It should be minimum. However you seem to have increased the clearance. Even 2 mm clearance you noted when you opened the pump was excessive. These pumps also have poor efficiency. The commonplace 0.5 HP mini monobloc pumps are of similar type, i.e. regenerative turbine type. These pumps are readily available. So, it would be a ready solution to replace the pump than to repair or rectify such tiny pump. Another option is to use a multistage pump. Pumps made in stainless steel sheet metal and in compact vertical version are becoming commonplace. Such pumps would give much more flow than 1000 lph, you are looking for. But if more flow is acceptable, you may not worry about the excess flow. Otherwise you may have to bypass the excess flow back to suction. Even with bypassing the excess flow, the pump may prove more energy-efficient than the regenerative type.
Q. We have 250 meters of pipe(1" sch40) existing for pumping water to our system and we have got some problem in our existing pump (centrifugal type, single stage, 2970 rpm). We have other spare pump of same rating and motor HP but its suction is of 32mm so my query is can we put expander in high speed centrifugal pump's suction (i.e 25mm X 32mm) because i have seen reducer in the suction side and expander in discharge side only. Will this effect in pump flow rate, discharge pressure, power consumption and cavitation in impeller. Or we will have to change whole piping or pump.
For trouble-free performance of pump, one should be concerned of friction losses on suction side. If present pump had 25 mm piping on suction side and has worked okay until it developed trouble, using a new pump with 32mm suction size along with an 25mmx32mm expander between 25mm pipe and 32mm pump suction should not give any new problem, since the expander would not add to the friction losses in suction. But better to have a long expander and fit it without increasing total length of suction piping.
Q. Collecting Data on Water Market. For the Academic Purpose I have to identify
1. Identify Market size
2. Identify Applications
3. Identify Consultants / Contractors.
Can you please send any of the old presentation on Water Market if you are having ready made?
Water market for pumps is too broad a subject. Following list identifies 26 situations where pumping water is inherent!
1) Large schemes for transmission of water from source to distant settlements. For example Mumbai gets water from Powai, Vihar, Tansa, Vaitarna lakes and from Bhatsa dam, which is about 60 km from Mumbai. Sardar Sarovar Scheme plans to take Narmada water to water-starved region of Saurashtra, And at National level special cell is set up to explore Interlinkage of rivers to benefit water-scarcity areas from water-surplus resources.
2) Domestic water supply. All municipal water supply systems guarantee water only into ground level reservoir. Pumping to households has to be managed by societies. Lakhs of mini monobloc pumps help people to steal water from municipal mains!
3) All water purification systems, whether of alum-dosing, sedimentation, flocculation, filtration, reverse osmosis etc. need pumps
4) Swimming pools, amusement parks, decorative fountains
5) Flood management
6) Fire fighting
7) Cooling water circulation in process plants
8) Boiler feed
9) Process water e.g. brines in paper mills
l0) Effluent treatment and disposal systems
ll) Sewage and waste water systems
12) Storm water or cellar drainage
13) Hydro-electric power generation or pumped storage power generation
14) Dewatering at construction sites
15) Dewatering in mines
16) Fluidised transport of ores
l7) Coal washeries
18) Dredging of river basins, canals, sea shores
19) Minor irrigation i.e. agricultural pumping
20) Lift irrigation or medium size irrigation
2l) Marine vessels, e.g. bilge water
22) Aquaculture ponds
23) Injection water for improving yieid, of oil wells
24) Heavy water in nuclear power plants
25) Water for high pressure jets for cleaning, gouging, cutting
26) Water in HVAC systems.
Residual Life of Pumps
Q. Our plant is one of the largest LPG unit in the country. most of the pumps are 20yrs old. The fluid handled by different pumps varies from c2-c3, lpg, crude oil, utility water, effluent water etc; can you suggest evaluation methods for fitness for service, analytical & practical method for residual life of pumps for replacement; present operating parameters(mech. & elect) and condition seems o.k based on condition monitoring observation. can you suggest some web sites or books for residual life analysis of process plant dynamic equipment?
Any pump has distinct zones, the wetted zone, the shaft-sealing zone, the bearing arrangement, the coupling and drive. In the wetted zone the pump casing is a pressure vessel and the residual life will be related to the wall-thickness. Pumps handling corrosive and abrasive fluids will have fast thinning of the all-thickness. The important component in the wetted zone is the impeller and the clearances at wearing rings. Wearing rings are of course replaceable parts and clearances can be redeemed to "like new" condition. Cavitation, erosion and corrosion are three major items that will be eating into the life of the impeller. Shaft-sealing zone is always attended to, whenever the leakage exceeds permissible and residual life gets revived with every refurbishment. Bearing life for journal bearings is theoretically infinite, because journal bearings a film of lubricant is supposed to be maintained all through the working of the bearing. If that is provided, there should be no wear and hence infinite life. For anti-friction bearings, the pump-designer selects the bearings, considering the axial and radial loads and desired bearing life, applying also the recommended factors for severity of service. Condition-based maintenance should be giving good indication of the condition of bearings. Most of the components of the "rotating assembly" are replacement spares. All replacements would redeem the residual life to "like new" condition. If so, scope for residual life analysis brings focus primarily to the pump casing, which should be looked at as a pressure vessel, where wall thickness becomes the guiding parameter.
Dosing Pumps & Gland Packing
Q. What are different types of Gland Packing? How does one determine their use? Under what conditions does one use Teflon and Asbestos Gland Packing? We have four Multiflo(V K Pumps) PR-10 Model Pumps that are used for dosing Chemicals in HRSG. Two Pumps serve as LP Dosing pump discharging Hydrazine+water solution at a Pressure of 4kg/cm2. The other two pumps are used as HP Dosing pump discharging Trisodium Phosphate solution at a pressure of 42 kg/cm2. Can we interchange these pumps? Can a LP Dosing Pump now discharging 4 kg/cm2 discharge at 42 kg/cm2 since both the pumps are of same models?
Usually the design of the 'liquid end' of reciprocating piston pumps is related to flow-rate, (volume per stroke multiplied by number of rokes per minute). Volume per stroke is cross-sectional area of piston multiplied by length of stroke. Mostly in a given model of pump, these parameters would be same. If so, one should be able to interchange pumps from one duty to another, provided the flow-rate is same. Pressure would influence the wall-thickness, especially of the cylinder. If that also is same, one can interchange more confidently.
Various types of Pumps & Applications
Q. Can you Please provide me the details of the following :-
1) Definition & Details of Operations of Centrifugal Pump - Also Industrial Applications
2) Details of Operations of Rotary & reciprocating pumps - Also Industrial Applications
3) Operations Details of Parallel & Series operations - Applications and Purpose.
4) Types of Vertical pumps and its operations
5) What the Difference between a Centrifugal Pump & Reciprocating Pump
A complete and comprehensive answer to the question amounts to writing a wholesome book on pumps, because the question asks for definitions and details for centrifugal, rotary and reciprocating pumps, vertical pumps and for applications including industrial. I think some commonplace examples will explain the three basic classes of pumps. The pump used to inflate the tyre-tube of a bicycle is a reciprocating pump. A to-and-fro motion is a reciprocating motion and all pumps where reciprocating motion is employed to do pumping action are reciprocating pumps. Swelling and shrinking motion of our heart t inhaling and exhaling is a motion similar to a reciprocating motion and we have diaphragm pumps working similar to our heart. Diaphragm pumps are also a type of reciprocating pump. The mini monobloc pumps used in many households are centrifugal pumps. Centrifugal pumps are very very commonplace and can be found everywhere, on the dug wells of farmers, in multi-storey residential premises for raising water from ground level reservoir to the overhead tank, etc. Pumps at petrol pumps for filling petrol or diesel in vehicles are most commonly rotary pumps, technically called as rotary positive displacement pumps.
Q. What are canned pumps?
The word "Canned" gets associated with pumps in two contexts - one, in respect of "Canned Motor Pumps" and another in respect of pumps handling volatile liquids like LPG, where a vertical pump has a can around it, deep enough to provide the NPSHr of the pump by virtue of the suction impeller getting as much positive head.
Q. Wanted some information on Osmotic / Osmatic Pumps.
From the name of your company you seem to be involved with water treatment. Reverse Osmosis is a process for purification of water by forcing the raw water through osmotic membrane. Osmosis is a natural phenomenon, by which thinner liquid will travel towards a thicker liquid, even if the two liquids are separated by a permeable membrane. But, for purification, raw water, which is thicker, has to travel across the membrane. This is contrary to natural phenomenon of osmosis. Hence the raw water is required to be forced. And the process is called Reverse Osmosis (RO). The pressure required is quite high, depending upon the content of impurities. RO is supposed to be the process capable of giving purest water, not allowing even micro-organisms to pass through. Because of high pressures, RO was not considered feasible for domestic usage. So, domestic water purification systems were based at best on purification with Ultraviolet rays. However over the last 6 to 8 years domestic RO systems are also available. RO systems have been used on ocean-going vessels since many years. Removal of salinity from sea water to make it potable is again most reliably achieved with RO. Pumps for RO system are in the entire range of sizes from those for domestic systems to even municipal water supply systems.
Axial Float
Q. How to calculate axial float in boilerfeed water multistage pumps.(with and without balancing disc) please enlighten me with diagrams.
Axial float is caused by the axial thrust. There is axial thrust even in single stage pumps. It gets multiplied and hence becomes more pronounced in multistage pumps. Basically axial thrust is caused by a differential pressure across an area. In a closed impeller area of the backshroud between the hub dia and eye diameter experiences suction pressure on one side and impeller's discharge pressure on the other side. This would cause the rotating assembly to be thrust forward towards the suction. In case of semi-open impellers, there is a pressure gradient all the way from the outside diameter of the impeller to the hub diameter. In case of vertical pumps, the total weight of the rotating assembly would also add to the axial thrust. Calculation of axial float will then be related to by what amount the axial thrust would displace the rotating assembly. In most designs the displacement will be arrested by the bearing clearance. Even commonplace deep groove ball bearings are also available in reduced or controlled clearance version and are used in pumps with semi-open impellers. Axial thrust apart from being a regular aspect of a running pump, it becomes a transient phenomenon during starting and stopping of pumps and would cause an impact onto the feature arresting the displacement, viz. bearing clearance or seating face of balancing disc. Balancing disc employs the same basic concept of axial thrust, it being caused by differential pressure over an area, but in the reverse direction. An extempore thought comes to mind that designers can try reducing wear due to transient impacts during starting and stopping, especially during stopping by providing a tapping from beyond the non-return valve to the balancing disc. This may be possible even in existing pumps. Most pumps with balancing-disc are with journal bearings. Hence the balancing disc only serves as the displacement arresting feature. It is susceptible to wear. Hence all balancing disc have a raised portion ring near the outside diameter of the disc. The maximum wear allowance is the height of the raised portion. This is marked on the shaft for easy monitoring by the user for the wear on the balancing disc. Since balancing disc operates with the principle of differential pressure over an area, it is important to ensure the pressure differential. The parallel faces between the balancing disc act as an orifice and cause the differential pressure. So the moving face needs to be set to give minimum clearance, but not so minimum as to cause rubbing. Secondly the throttled pressure has to be tapped off. Otherwise the balancing disc area will just become a pressure vessel and the pressure will balance and there will be no differential pressure to balance the axial thrust. So the line tapping off the throttled pressure should not get clogged. Wear from the balancing disc is itself liable to cause clogging.
Selection of Pump for Agriculture Application
Q. I noticed your detailed question and answers in the magazine from that I am willing to clear my doubts I am a farmer, farming about 60 acre with coconut and sapota groves. I am having part of the land near by a river and a part of the land too far. for that I planned to pass water by underground pipe line, the distance is 2 km approx. with a maximum head of 37 feet discharge height, suction head may be around 15 feet height. I planned to use the underground pipe water by dumping
the local wells before irrigation. for that, 1.What type of pump is needed.
2. How much capacity is needed.
3. Power consumption
4. I planned to use PVC/HDPE in underground (which one is better), GI in open area.
5. Give the pipe dimension throughout the distance Suppose: If I directly irrigate by using drip irrigation (the line provided for drip irrigation is 3" for the whole land)
1. What type of pump is needed
2. Capacity,- power?
3. Pipe material of construction?
4. Give the dimension of pipe throughout the distance
5. Kindly mention the number of air vent valves to be provided.
You have mentioned that you find my answers 'detailed'. Your question has prompted really the 'most detailed' answer! Your question gave me the opportunity of bringing out also the cost, which the nation bears for providing power to agriculture. Thank you hence for your question. It is true that over the last 50 years our country has become self-sufficient in food. The nation is indebted to the farming community for that. But the nation has also borne very heavy cost for providing the power. And it has not been used any intelligently or efficiently by the farming community. There is rampant dishonesty, what with stealing of power! The power supply system cannot manage the quality of power against so much of stealing. And we grumble of very low voltages, fluctuations and trippings. Pump manufacturers end up designing pumps and motors to withstand these vagaries of power, hence that much costlier motors and as much inefficient motors. All these hidden costs finally usurp the pockets of the entire population of the country. Hope, you would find the appropriate methodology for making the right selection of pump. But you may have to do all the calculations all over, especially wherever the assumptions are not correct.
For a ready reference, the assumptions made are as follows.
1) Water requirement for coconut is assumed as 100 mm every fifteen days.
2) Water requirement for drip irrigation is assumed at one-fourth of the above.
3) Frictional head for GI pipe only is taken for illustration. You may check for other pipes, especially HDPE.
4) Other frictional heads for losses in foot valve, non-return valve, bends, etc. are not taken into account.
5) The illustration considers only pumping river water to local wells. Another pump will be required for pumping from local well to the field.
6) Assumption also is made to run the pump for eight hours per day.
7) Percolation in local well(s) or yield of local well is assumed to be 5 liters per second.
8) Total length for pipeline considered is 2 km.
All this procedure of selecting an agricultural pump and composing the system is also covered in Indian Standards IS-9694 Part 1 and IS-10804. Of these IS-10804 also gives ready data about frictional heads for different types of pipes.
For selecting a pump one has to first find out the required discharge and head. Discharge is a rate and not a total quantity. Suppose your 60 acres of land should be fed with 4 inches (100 mm) of water in one irrigation cycle, to find total quantity of water, which will have to be pumped, we would first get all data in proper units.
60 acres = 60*4840 sq. yards = 60*4840*9 sq. ft = 60*4840*9/3.28/3.28 sq. m. Then4 inches (100 mm) of water over this much area means 60*4840*9/3.28/3.28 *0.1 = 24293.6 cubic meters of water. Now you would not be able to irrigate all the 60 acres of land in one day. If you would irrigate say 4 acres per day, so that every acre would get water once in every 15 days, then 4 acres of land would need 24293.6/15 = 1620 cubic meters of water. This will vary. If every acre should get water once in every 10 days, 6 acres will have to be irrigated everyday. Then water to be pumped every day would be 2430 cubic meters. Again I just assumed water requirement as 4 inches in one irrigation cycle. It would be different for different crops and would be different for different methods of irrigation. In drip irrigation, the water requirement could be only one-fourth of that for furrow irrigation. You are planning for coconut and sapota. Now if sapota is to be a crop by inter-cultivation, it would not need separate feed of water. It would share from what is fed to coconut. You will have to check whether this assumption would be correct in drip irrigation, because, in drip irrigation, one feeds water to the root of one plant. So, if coconut takes all the water that is fed at its root, it would not leave any water for sapota. However, it is not practical to lay drip tubing to the root of every sapota plant. Maybe you may feed some extra water to coconut. The irrigation cycle itself would be different in different seasons. For example during summer the interval would have to be water every week, whereas in winter it could be water every three weeks. For pumping requirement one should consider the shortest cycle or interval. I do not have data about requirement of water for coconut. I assumed 4 inches every fifteen days to illustrate the method of calculation. To proceed with calculation, for feeding 1620 cubic meters per day, by running the pump for 8 hours every day, the flow-rate required of the pump would be 1620/8 = 202.5 cubic meters per hour = 2700 liters per minute = 45 liters per second. If drip irrigation would need only one-fourth, it would be 11.25 liters per second. It is logical to use drip irrigation for coconut, because once planted, coconut would grow for years unending. With most other crops like jowar, rice, wheat, sugarcane, etc., the field has to be ploughed and tilled every season. Drip tubing would also get uprooted and will have to be re-laid. This would be a problem even with sprinkler irrigation. This, I guess is the reason, why drip or sprinkler irrigation does not become feasible for many crops, though requirement of water is very economical for these methods of irrigation.
Please note that all the calculation is done assuming all 60 acres being at one place. But it is not so, as you have mentioned. It would be better to do separate calculation for the peice of land near the river and for the one 2 km away. Actually you plan to put water from the river into the wells in the field away from the river. Those wells will have some yield or rate of percolation of their own. If the total yield of the wells is 5 liters per second, then for drip irrigation you would need pumping only 6.25 liters from the river, even if all 60 acres are away from the river.
Anyway, having illustrated calculation to find the discharge for the pump, on to finding the head. You have mentioned maximum 37 feet height above the land near the river and 15 feet depth for drawing water from the river. That makes total height 52 feet = 15.85, say 16 meters. If 6.25 liters per second are to be pumped across 2 km distance, assuming farthest well is at 2 km, the frictional head in a 2.5 inch GI pipe would be 5.7 meters for every 100 meters, so for 2 km, total 114 meters. Instead if one would use 3" pipe it would be only 2.1 meters for every 100 meters, hence 42 meters and for 4" pipe at 0.7 meters for every 100 meters only 14 meters. Adding the frictional head to the height of lifting, 16 meters, the total head for the pump would be 130 meters for 2.5" pipe, 56 meters for 3" pipe and only 30 meters for 4" pipe.
You have also enquired about the type of pipe to be used, whether GI, PVC or HDPE? The issues involved are durability of the pipe, smoothness of the pipe, size or actual inside diameter of pipe and cost of pipe. In case of PVC or HDPE pipes, actual inside diameter is more important than just the size of pipe. Both PVC and HDPE pipes will be smoother than GI, but will have smaller actual inside diameter. Smoothness reduces the frictional head, but less inside diameter increases the frictional head. You would have noticed above that for 3" inside diameter the frictional head is only 2.1 meters for every 100 meters, but increases to 5.7 meters for every 100 meters for 2.5" inside diameter. In respect of durability, PVC is least durable, especially if it is exposed to ultra-violet rays from the sun. There is also the menace of the rats and rodents and you have to protect 2 km long pipe from them. For putting the pipe underground you would have to dig a trench. All that labour would not be needed for taying over-ground. From connsiderations of durability, safety and maintainability, cost of installation including cost of making trench, GI pipe may still be an option to keep in mind.
Coming to motor HP, to pump 6.25 liters per second against 56 meters total head for 3" GI pipe, assuming pump efficiency of 50 percent, one would need 6.25*56/75/0.5 = 9.3 HP, say 10 HP. Pump for same 6.25 liters per second but against total head of 130 meters for 2.5" pipe is likely to be less efficient say pump-efficiency of only 40%. Then motor HP will be 6.25*130/75/0.4 = 27.03 HP, say 30 HP. In fact if you can put pumps in series, at some distance, say at every 600 meters along the pipeline, with 3" pipe the head per pump can be only 19m. Each pump can be more efficient, say, 60%, then motor HP of each pump would be 6.25*19/75/0.6=2.64, say 3 HP. So, one can manage the situation with 3 pumps of only 3 HP each than one pump of 10 HP. And you will appreciate that 3 HP pumps are more commonly available, better mass-produced and hence more competitively priced than one 10 HP pump. Getting spares and repairing and maintenance of 3 HP pumps will be cheaper and more easily manageable than for 10 HP pump. With 4" pipe, requiring total head of only 30 meters, the motor HP required assuming only 50% efficiency would be 6.25*30/75/0.5 = 5 HP. Well, only one 5 HP pump, but 2 km of 4" pipe!
Now there is also the cost of power. Even if this may not be a significant cost to a farmer, the nation bears the cost, say, some Rs. 2 per unit of power, as the cost of generating the power and transmitting it to the ultimate user. For irrigating coconut you will run the pump for 9 months of the year, leaving out 3 months of monsoon. This means using the power at 8 hours per day, for 270 days i.e. for 2160 hours per year. If efficiencies of 3 HP (2.2 kW), 5 HP (3.7 kW) and 10 HP (7.5 kW) motors are taken as 80%, 85% and 90% respectively, for three, one and one number of 3, 5 and 10 HP pumps respectively, the energy consumed comes out to 3*2.2/0.8*2760 = 22,770 units for 3 Nos. 3 HP pumps, 3.7/0.85*2760 = 12014 units for one, 5 HP pump and 7.5/0.9/*2760 = 23000 units. So ANNUAL cost to the nation is Rs. 45540, Rs. 24028 and Rs. 46000 respectively. If the coconut field will be bearing fruit for 45 years after initial gestation of 5 years, irrigating the field for 50 years would cost the nation Rs. 11.385 lakhs, Rs. 6 lakhs and Rs. 11.5 lakhs respectively. The discussion above has brought forth different cost involved, cost of pump, cost of pipe, cost of laying the pipe, periodic cost of spares, repairs and maintenance and the cost of power. Even if a farmer would want to leave out the cost of power, the total of other costs calculated over an average period of 15 years, it would be a good idea to work out the Life Cycle Cost for different options and then make the most economical decision.
Q. What factors will get affected if pipe size of 50mm suction & delivery is used for a pump having flange sizes 100mm by 100mm. Will it harm the pump in any way or will only the discharge get affected?
Frictional loss in 50 mm pipe will be 32 times higher than that in 100 mm pipe! This is wastage of energy. Cost of installation will be cheaper with 50mm pipe. But wastage of energy will happen for the life of the system. Also, if a pump is pumping with a suction lift of, say 6m, and ence effective pipe length of say, 8m and required flow-rate is 6 1/s, the friction loss in 50mm pipe will be 1.5m as against only 0.05m for 100 mm pipe. With further losses in strainer and footvalve and bend and eccentric reducer, etc. the pump may suffer cavitation.
FIELD PROBLEMS
Q. We are regular reader of your Pump magazine. We are encouraged to see your response for different problems related to pumps faced in industries and suggestions sought from you. We are referring one of our specific pump related problem. We will like to have your comments on it. We have a multi stage steam condensate pump in our Urea plant which takes suction from tank at atmospheric pressure and discharges it at 45 Kg/CM2. This pressurised condensate is used at different locations in the plant for different purposes . Now due to some change in process conditions we require condensate pressure up to 32 kg/cm2 only. As pump is discharging at 45 kg/cm2 it is unnecessary loss of electrical energy. We are thinking to remove 2 or 3 impellers to reduce the discharge pressure.
Please tell us whether this is possible or not? What other problems we may face?
What is the general formulae to get the relation between number of stages and pressure delivered a pump?
Pump details are as follows:
Stages : 8 Impeller dia - 180 mm (same for all) Impellers are in series Balance drum provided at discharge end with a balance line d/s of this drum to suction line, Speed: 3000 rpm Intermediate bearing sleeve provided. Capacity : 20 m3/Hr
General relationship between pressure and number of stages is of direct proportion. You have 8 stages for 45 bar. Hence number of stages for 32 bar = 32*8/45=5.69 say 6. So, you can remove 2 stages! With 6 stages you would get 6/8*45=33.75 bar pressure. Power saving will also be in direct proportion. Assuming 60% pump efficiency, at 45 bar pressure and 20 m3/h the input power to pump is 20*45*10.336/270/0.6=57.25 HP. If you have a 75 HP motor, presently it is loaded to 76 oad. At 34 bar for 20 m3/h with same 60% efficiency, the loading of the motor will be 20*34*10.336/270/0.6=43.4 HP only 57.8%. Efficiency of 75 HP motor at such part load operation will be less. To get full benefit of reducing number of stages, you may use a 50 HP motor. You may check whether pump efficiency given in pump characteristics from manufacturer is 60% and accordingly whether using 50 HP motor will be appropriate. Actually manufacturer might have given you pump characteristics with different number of stages also.
Q. The axial flow pump of capacity 7700m3/hr it installed in CLOSED LOOP system under 100 mbar abs vacuum in our plant. When pump was first trial run we observed severe cracking sound in the pump and thought for the possible cavitation due to starvation of pump. The pump was than stopped, acid drained, and on inspection some rubber pieces were found at pump discharge end. Thus, it was thought that these rubber piece were probably causing the abnormal sound. After having carried out the rubber repair of the vessel the pump was re-started Before starting the pump we ensured that the liquid level is up to the desired operating level and Initially the sound was low and intermittent but when vacuum was pulled up to 100 mbar abs. the sound increased abnormally and became continuous. Pump was stopped immediately we took second trial run but, the observations are same i.e., heavy cracking & metallic sound in the pump. We have now stopped the pump. We feel there is some design problem with the pump & its application.(NPSH ?)
Axial flow pumps are essentially high specific speed pumps. And high specific speed pumps would have high NPSHr. No designer can design an axial flow pump with low NPSHr. Vacuum at suction is only making the matter worse. Heavy crackling metallic sound is typical of a pump suffering from cavitation. Since there cannot be a design with low NPSHr, only option is to explore how NPSH available can be improved, so as to have positive margin over NPSHr. Options to be explored seem to be as follows.
1) Whether suction vessel can be at higher elevation above the pump.
2) Whether pump can be lowered to a level below the suction vessel
3) If there is a throttling valve at suction to adjust vacuum at suction, whether the valve can be eliminated or whether the friction loss across the valve can be reduced by using a ball valve and preferably of higher size.
4) Whether the piping on the suction side with all appurtenances like bends, tees, valves can be of higher size
5) Whether vacuum can be less stringent
6) If liquid being handled is at temperature higher than ambient, whether a heat exchanger can be added to cool the liquid to bring down the temperature. Since the pump is in a closed loop, rise in temperature of the liquid circulating in a closed loop is a natural phenomenon. Your observation that the pump starts off okay but noise aggravates after some running is indicative of rise in temperature causing vapour pressure of the liquid going up, thereby promoting cavitation. A heat exchanger to cool the liquid before it gets back into the suction vessel should then help.
Q. In our system we require chilled water at 1000lit/hr and 40-60psig pressure at 7.0deg centigrade. Original pump was centrifugal type with open type straight vane impeller, 2900rpm, single stage pump Due to some reason we had to relocate the pump and chiller and piping length was increased by 30mtr but elevation of pipe was same but when we opened the pump for inspection we found its impeller vane(03 nos) got broken also impeller to casing clearance was 2.0mm so we changed the impeller with new one and dia of new impeller was 1.0mm higher then old one but during functioning pump discharge pressure has dropped to 45psig and flow rate 350lit/hr also rubbing marks were found on impeller vanes so we increased the impeller to suction casing clearance by 0.5mm and pump flow has increased to 450 lit/hr but pressure further dropped to 25psig due to which we can't get the cooling system working properly we also shifted the pump near to system by increasing its suction line and reducing its discharge line since suction water tank of chiller is at higher level then pump center line but condition is same kindly tell me the correct method to increase the discharge pressure and flow of the pump.
For the small discharge and relatively high pressure, the pump ought to be a regenerative turbine type centrifugal pump (IS-8472). You have also mentioned straight vanes, which is typical of these pumps. The performance of these pumps is very sensitive to clearance between casing and impeller. It should be minimum. However you seem to have increased the clearance. Even 2 mm clearance you noted when you opened the pump was excessive. These pumps also have poor efficiency. The commonplace 0.5 HP mini monobloc pumps are of similar type, i.e. regenerative turbine type. These pumps are readily available. So, it would be a ready solution to replace the pump than to repair or rectify such tiny pump. Another option is to use a multistage pump. Pumps made in stainless steel sheet metal and in compact vertical version are becoming commonplace. Such pumps would give much more flow than 1000 lph, you are looking for. But if more flow is acceptable, you may not worry about the excess flow. Otherwise you may have to bypass the excess flow back to suction. Even with bypassing the excess flow, the pump may prove more energy-efficient than the regenerative type.
Q. We have 250 meters of pipe(1" sch40) existing for pumping water to our system and we have got some problem in our existing pump (centrifugal type, single stage, 2970 rpm). We have other spare pump of same rating and motor HP but its suction is of 32mm so my query is can we put expander in high speed centrifugal pump's suction (i.e 25mm X 32mm) because i have seen reducer in the suction side and expander in discharge side only. Will this effect in pump flow rate, discharge pressure, power consumption and cavitation in impeller. Or we will have to change whole piping or pump.
For trouble-free performance of pump, one should be concerned of friction losses on suction side. If present pump had 25 mm piping on suction side and has worked okay until it developed trouble, using a new pump with 32mm suction size along with an 25mmx32mm expander between 25mm pipe and 32mm pump suction should not give any new problem, since the expander would not add to the friction losses in suction. But better to have a long expander and fit it without increasing total length of suction piping.
Q. Collecting Data on Water Market. For the Academic Purpose I have to identify
1. Identify Market size
2. Identify Applications
3. Identify Consultants / Contractors.
Can you please send any of the old presentation on Water Market if you are having ready made?
Water market for pumps is too broad a subject. Following list identifies 26 situations where pumping water is inherent!
1) Large schemes for transmission of water from source to distant settlements. For example Mumbai gets water from Powai, Vihar, Tansa, Vaitarna lakes and from Bhatsa dam, which is about 60 km from Mumbai. Sardar Sarovar Scheme plans to take Narmada water to water-starved region of Saurashtra, And at National level special cell is set up to explore Interlinkage of rivers to benefit water-scarcity areas from water-surplus resources.
2) Domestic water supply. All municipal water supply systems guarantee water only into ground level reservoir. Pumping to households has to be managed by societies. Lakhs of mini monobloc pumps help people to steal water from municipal mains!
3) All water purification systems, whether of alum-dosing, sedimentation, flocculation, filtration, reverse osmosis etc. need pumps
4) Swimming pools, amusement parks, decorative fountains
5) Flood management
6) Fire fighting
7) Cooling water circulation in process plants
8) Boiler feed
9) Process water e.g. brines in paper mills
l0) Effluent treatment and disposal systems
ll) Sewage and waste water systems
12) Storm water or cellar drainage
13) Hydro-electric power generation or pumped storage power generation
14) Dewatering at construction sites
15) Dewatering in mines
16) Fluidised transport of ores
l7) Coal washeries
18) Dredging of river basins, canals, sea shores
19) Minor irrigation i.e. agricultural pumping
20) Lift irrigation or medium size irrigation
2l) Marine vessels, e.g. bilge water
22) Aquaculture ponds
23) Injection water for improving yieid, of oil wells
24) Heavy water in nuclear power plants
25) Water for high pressure jets for cleaning, gouging, cutting
26) Water in HVAC systems.