Frequently Asked Question-29
- By Jayesh Patel
- Published 02/1/2010
Tech Quest
Q. I am working in ESSAR OIL, working as a maintenance engineer in CDU/VDU units in Refinery located at Vadinar.
I would like to know the following:
1. After vaporization of any lube oil which we are using in over hung C.F. pumps in our refineries, how much % reduction in viscosity of lube oil and what wilt be the adverse affect of presence of condensed drops in bearing housing?
2. what are parameters we are checking while doing oil analysis? And what are the problems upcoming in any equipment either pump or compressor?
3. How much % of tife of any equipment will be increased by predicting and attending of upcoming problems indicated by the result of oil analysis
1.) After vaporization of any lube oil which we are using in over hung C.F. pumps in our rifineries, how mach % reduction in viscosity of lube oil
Different grades of lub oil have different temperature v/s viscosity relationship.
Query 1a and what will be the adverse affect of presence of condensed drops in bearing housing?
Presence of condensation not only affects the lubricity of oil, condensation will also cause corrosion of shaft.
2.)what are parameters we are checking white doing oil analysis?
Lube oils are to be checked for viscosity and ingress of foreign matter into the oil.
Query 2a And what are the problems upcoming in our any equipment either pump or compressor?
Lack of lubrication will cause any equipment to suffer high friction, rise in temperature, damage or breakage to bearings and shafts
3.) How much % of life of any equipment will be increased by predicting and attending of upcoming problems indicated by the result of oil analysis.
Proper lubrication is only one of the causes of failure of a pump. Even if the lubrication is proper, a pump may fail due to other causes, such undue vibration, cavitation, misalignment, leakage at shaft-seal, improper operation, especially, operation at low flow, etc. philosophy of predictive maintenance is to monitor condition of the pump for all these critical parameters and achieve lengthening of Mean Time Between Failures (MTBF
Q. I have a query regarding the leakage current test in submersible motors (3 phase).
There are two methods i suppose: -1st :- By using a mille ampere meter. Connect one wire of mille ampere meter to motor body and the other wire to earth. Now give rated supply to motor (no load). Take the reading of mille ampere meter which is supposed to be leakage current of that particular submersible motor.
2nd :- By using the commercially available leakage current meters. Connect one wire of this leakage current meter to one of the phases i.e R,Y or B and the other wire to earth. The reading of leakage current meter is taken as the value of leakage current. Now the question is which of these methods is correct?
I performed the leakage current test at my factory premises by using both of the above methods. The values I got were not same. People at ERDA, Vadodara are using the 2nd method. But the being an electrical engineer doesn't find anything wrong with the first method, which appears to be logically correct to me.
I too would feel that method 1 is more appropriate. Leakage current, to my mind, is current which is escaping from such point on the motor, from where current is not supposed to theoretically leak. Appropriate point then is the motor body.
Worry about the leakage current is also a consideration of safety. Leakage of current on motor body ought to be within safe limit. From this view-point also motor body appeals to be more appropriate point. I am replying from logical considerations. One needs to check up, whether standards do specify any exact method and location. If the standards do not specify clearly, then logic should prevail.
Q. Could you please give some info on the following, For a closed a loop chilled water system, if the elected pump's head is more than the required (Say selected pump's head is 4.5 bar and actual head requirement is only 3,5 bar) what are the possible damages to the system ?
If at desired flow, Q, system needs 3.5 bar and pump curve shows 4.5 bar, the pump will operate at much higher flow and would possibly overload the motor.
If the pump has to feed a chemical, say an alkali to neutralise an acid, excess flow will make the chemical reaction to yield an alkaline end-product, instead of neutralisation.
To set the system at desired flow, one can either throttle the valve or trim the impeller or reduce the speed.
Throttling the valve is not efficient way of doing the setting. Also, on throttling the valve, the pressure seen on the gauge is before the valve and not after the valve, If one puts a gauge after the valve also, one would notice that, that gauge would not show any alarming pressure.
In most applications, one is more concerned of the flow desired, than the pressure. And one should be also concerned f or overloading of the motor. Options tor getting desired flow and containing overloading are the three options mentioned above.
Q. I am your regular subscriber since long. I have a query about selection of pumps . kindly guide me the best pump according to my requirement-
We have to suck clean water from river like open water canal. Currently we have installed Lubi make 30 HP V10 submersible of 1 stage 6" delivery giving about 4500-5000 lpm. Now we want to installed any big pump that gives the about 15000 lpm.
Horse power- no bound may be up to 50 hp Source- Suck Open clean water from river
Height- 17-20 mtr
Water requirement- 15000-20000 lpm
Type- Submersible or any electric pump
Data is not quite clear, especially about static head. An accurate estimation of total head should be done before selecting a pump. Since the pumping is from a canal, the level on suction side may not be varying much. Also level to which water is to be raised also may be a fixed level. The distance to which water is to be carried needs to be taken into account. Different sizes of delivery pipe would give different frictional head.
Efficiency of the motor should also be a point of consideration. Basically a dry weather proof motor may be more efficient than a submersible motor, Alternatively, a dry submersible motor, as in sewage submersible pumps can also have efficiency competitive with weather proof motor.
Assuming levels will remain same and in turn total head will remain same, for 3 times flow (15,000 lpm in place of 4500 to 5000 lpm at present) would need 3 times motor hp, hence nearly 90 to 100 hp. So 50 hp would not be adequate.
There can be an option of using more than one pumps. A large pump of 15,000 lpm would anyway be a new larger installation. Instead, one can consider modular enhancement of existing installation. Maybe a close-coupled vertical pump with dry submersible motor or a sump type or vertical turbine type pump with weatherproof motor could be also considered. If a pump-room or jack well can be constructed and if the suction lift is about 4 or 5 meters, even a horizontal split casing pump with normal horizontal motor could be considered.
The situation seems to be a good example for exploring number of options and making Life Cycle Costing of various options, before making final selection.
Q. For vertical Centrifugal Pumps (vessel mounted), is writing "Flooded suction" a correct statement or actual estimated NPSHA should be indicated?
It is always good practice to mention NPSHa. Some pumps need minimum submergence. Mere fact of suction being flooded, may not yet provide "minimum submergence". Inadequate submergence can become cause for cavitation.
For volatile liquids of high vapour pressure also, just flooded suction would be inadequate NPSHa. For example, for pumps for pumping LPG or for pumps for condensate extraction, purchase specifications would often declare NPSHa = zero, implying that the pump design should be taking care of NPSHr and required margin in the design itself. The design of pumps for such applications is often made "encastre" type.
Q. What is bearing crush? how do you check bearing crush?
(Additional Information : This question was replied in Pumps India, Jan/Feb 07 issue, however we have received more information on it from Mr Rai, we are thankful to him for his contribution).
Regarding bearing crush. In this context I would like to add that this term is used for the interference of the leeve type bearings either with sphericai seating or ylindrical seating. Out side diameter of the sleeve type bearing inserts are slightly higher than the inside diameter of the bearing housing. To achieve this the diameter of the two halves at the position perpendicular to the parting plane is higher than the diameter at the position across the parting plane. This difference is termed as Bearing Crush. This serves in the following ways.
It gives tight fit of the inserts into the bearing thus preventing any movement of the bearing insert. It prevents lube oil to be filled in-between the insert and bearing housing thus better heat transfer from the bearing. To avoid the oil clearance being decreased it is of utmost importance to take oil clearance measurement after assembly.
It is written to share the information and should not be taken otherwise.
Q. We are one of the leading blood bank equipment manufactures in India. We are using a pump of 28watts,230v,50Hz single phase AC for one of our equipment. but we are frequently getting the complaints from the field especially leaking through the shaft sealants, Can you suggest me a suitable pump for our use.
28W, 230V, 50 Hz, single-phase becomes more the specification of the motor than the pump. For the pump, the specification should mention flow-rate and pressure, and also the liquid characteristics, obviously blood. Blood is a highly viscous liquid and also needs to be handled hygienically. I think a pump to handle blood hygienically should be a positive displacement pump preferably of the diaphragm type or peristaltic type, which are inherently seal-less and leak-less. This is of course a general recommendation. This can be better fine-tuned, if you would detail the flow-rate and pressure.
Q. Thank u for the valuable information the requirement is not for the use in circulation of blood. we required it for circulation of water at a temperature of 56 degree in one of our equipment called Plasma thawing bath. we want the pump spec of head 4.5M and LPH -300.
Since you had earlier mentioned about the problem of leakage with these pumps for Plasma Thawing Bath, I would recommend a pump with vertical motor. Such pump is used in circulating machine tool coolant in machine tools, such as lathes, drilling machines or CNC lathes, etc. The height to be delivered is about same as 4.5 m mentioned by you and the discharge is also of similar order as 300 lph. Pumps on machine tools also handle circulating coolant, which often could be hot after contact with metal-chips machined by the machine. As such 56 Deg C is not a very hot temperature for most common materials used in pump-construction.
Other similar pump is one, used in Desert coolers. For pumps for desert coolers, there has even been an Indian Standard IS-11951, where the pumps lifts the water from the tray in the bottom to the tray on the top, so that people can get cool breeze from the air blown by the fan across a curtain of the fragrant grass.
Pumps of machine tool coolant and of desert cooler are made by many, many people. For your application, to be free of leakage problem, they should be vertical, whereby the pump stays submerged in the hot water sump.
Hope, this helps.
Q. We Manufacture Domestic selfpriming and Centrifugal pump during the test of centrifugal pump of 1.5 hp 2 x 2 The following is the observation. Impeller OD 125 mm Pump over heated in 240 v and tripped of after running for six hour Reduced OD to II8 mm 240 v pumps is ok 220 v it tripped off after an hour Impeller OD reduced to 117 mm 240 v and 220 it is ok but tripped off at 180v we do not want to apply this method by reducing the OD of the impeller. What is the reason for the tripping off Was it required to reduce the impeller od by doing so will the performance of the pump get affected. Please advise with the solution.
Tripping off of the motor is due to overload. With regenerative turbine type impellers in domestic, self-priming centrifugal pumps, it may prove effective to try reducing the impeller width by facing from both sides and redoing the assembly maintaining the original clearances.
Q. Thanks for the reply sir, can this method applied for centrifugal agri monobloc pump, by doing facing on both the sides, Will the centre point of the vanes with the volute can be maintained pls clarify.
No. The design logic of commonplace centrifugal pumps is totally different. By the way, have you already tried facing the impeller of regenerative turbine type impeller? What percentage change in width has given what change in power? I shall be curious to learn of the trials.
Q. One of our customer using centrifugal (end suction)pump to pumping the hexane from underground tank, they have facing cavitation problem. Pipe line arranged on the top of tank. Pls, advise how to avoid the cavitation
Most effective solution would be to change over to a vertical sump pump, which will work submerged in the liquid. The pump should stay submerged even with the minimum liquid level. Such pump will eliminate suction piping, footvalve, cavitation and re-priming at every loss of prime.
Q. Kindly tell me the formula for horizontal piston pumps, available in single, double and triple pistons. how can v calculate the discharge at the pump at given pressure. for eg. a pump with suction capacity of 36 lpm and max Rpm 950. how can v calculate the discharge of pump at diffirent pressures by using their pulley sizes etc.
Discharge of a piston pump is basically (area of piston * stroke length * rpm)
Maximum Pressure = HP*k*Pump efficiency/Q/(sp. gr.)
k = constant appropriate to the units used for power and Q
For pump efficiency one shall have to consult the pump-manufacturer.
For multiplex pumps, total Q=Q per piston*no. of pistons, if their strokes are in phase.
Mostly they will NOT be in phase. Then the calculation becomes complex. Ideally one may have to make "discharge versus time" plots for each piston and derive a summation plot, keeping in mind the phase differences.
Q. I am working in ESSAR OIL, working as a maintenance engineer in CDU/VDU units in Refinery located at Vadinar.
I would like to know the following:
1. After vaporization of any lube oil which we are using in over hung C.F. pumps in our refineries, how much % reduction in viscosity of lube oil and what wilt be the adverse affect of presence of condensed drops in bearing housing?
2. what are parameters we are checking while doing oil analysis? And what are the problems upcoming in any equipment either pump or compressor?
3. How much % of tife of any equipment will be increased by predicting and attending of upcoming problems indicated by the result of oil analysis
1.) After vaporization of any lube oil which we are using in over hung C.F. pumps in our rifineries, how mach % reduction in viscosity of lube oil
Different grades of lub oil have different temperature v/s viscosity relationship.
Query 1a and what will be the adverse affect of presence of condensed drops in bearing housing?
Presence of condensation not only affects the lubricity of oil, condensation will also cause corrosion of shaft.
2.)what are parameters we are checking white doing oil analysis?
Lube oils are to be checked for viscosity and ingress of foreign matter into the oil.
Query 2a And what are the problems upcoming in our any equipment either pump or compressor?
Lack of lubrication will cause any equipment to suffer high friction, rise in temperature, damage or breakage to bearings and shafts
3.) How much % of life of any equipment will be increased by predicting and attending of upcoming problems indicated by the result of oil analysis.
Proper lubrication is only one of the causes of failure of a pump. Even if the lubrication is proper, a pump may fail due to other causes, such undue vibration, cavitation, misalignment, leakage at shaft-seal, improper operation, especially, operation at low flow, etc. philosophy of predictive maintenance is to monitor condition of the pump for all these critical parameters and achieve lengthening of Mean Time Between Failures (MTBF
Q. I have a query regarding the leakage current test in submersible motors (3 phase).
There are two methods i suppose: -1st :- By using a mille ampere meter. Connect one wire of mille ampere meter to motor body and the other wire to earth. Now give rated supply to motor (no load). Take the reading of mille ampere meter which is supposed to be leakage current of that particular submersible motor.
2nd :- By using the commercially available leakage current meters. Connect one wire of this leakage current meter to one of the phases i.e R,Y or B and the other wire to earth. The reading of leakage current meter is taken as the value of leakage current. Now the question is which of these methods is correct?
I performed the leakage current test at my factory premises by using both of the above methods. The values I got were not same. People at ERDA, Vadodara are using the 2nd method. But the being an electrical engineer doesn't find anything wrong with the first method, which appears to be logically correct to me.
I too would feel that method 1 is more appropriate. Leakage current, to my mind, is current which is escaping from such point on the motor, from where current is not supposed to theoretically leak. Appropriate point then is the motor body.
Worry about the leakage current is also a consideration of safety. Leakage of current on motor body ought to be within safe limit. From this view-point also motor body appeals to be more appropriate point. I am replying from logical considerations. One needs to check up, whether standards do specify any exact method and location. If the standards do not specify clearly, then logic should prevail.
Q. Could you please give some info on the following, For a closed a loop chilled water system, if the elected pump's head is more than the required (Say selected pump's head is 4.5 bar and actual head requirement is only 3,5 bar) what are the possible damages to the system ?
If at desired flow, Q, system needs 3.5 bar and pump curve shows 4.5 bar, the pump will operate at much higher flow and would possibly overload the motor.
If the pump has to feed a chemical, say an alkali to neutralise an acid, excess flow will make the chemical reaction to yield an alkaline end-product, instead of neutralisation.
To set the system at desired flow, one can either throttle the valve or trim the impeller or reduce the speed.
Throttling the valve is not efficient way of doing the setting. Also, on throttling the valve, the pressure seen on the gauge is before the valve and not after the valve, If one puts a gauge after the valve also, one would notice that, that gauge would not show any alarming pressure.
In most applications, one is more concerned of the flow desired, than the pressure. And one should be also concerned f or overloading of the motor. Options tor getting desired flow and containing overloading are the three options mentioned above.
Q. I am your regular subscriber since long. I have a query about selection of pumps . kindly guide me the best pump according to my requirement-
We have to suck clean water from river like open water canal. Currently we have installed Lubi make 30 HP V10 submersible of 1 stage 6" delivery giving about 4500-5000 lpm. Now we want to installed any big pump that gives the about 15000 lpm.
Horse power- no bound may be up to 50 hp Source- Suck Open clean water from river
Height- 17-20 mtr
Water requirement- 15000-20000 lpm
Type- Submersible or any electric pump
Data is not quite clear, especially about static head. An accurate estimation of total head should be done before selecting a pump. Since the pumping is from a canal, the level on suction side may not be varying much. Also level to which water is to be raised also may be a fixed level. The distance to which water is to be carried needs to be taken into account. Different sizes of delivery pipe would give different frictional head.
Efficiency of the motor should also be a point of consideration. Basically a dry weather proof motor may be more efficient than a submersible motor, Alternatively, a dry submersible motor, as in sewage submersible pumps can also have efficiency competitive with weather proof motor.
Assuming levels will remain same and in turn total head will remain same, for 3 times flow (15,000 lpm in place of 4500 to 5000 lpm at present) would need 3 times motor hp, hence nearly 90 to 100 hp. So 50 hp would not be adequate.
There can be an option of using more than one pumps. A large pump of 15,000 lpm would anyway be a new larger installation. Instead, one can consider modular enhancement of existing installation. Maybe a close-coupled vertical pump with dry submersible motor or a sump type or vertical turbine type pump with weatherproof motor could be also considered. If a pump-room or jack well can be constructed and if the suction lift is about 4 or 5 meters, even a horizontal split casing pump with normal horizontal motor could be considered.
The situation seems to be a good example for exploring number of options and making Life Cycle Costing of various options, before making final selection.
Q. For vertical Centrifugal Pumps (vessel mounted), is writing "Flooded suction" a correct statement or actual estimated NPSHA should be indicated?
It is always good practice to mention NPSHa. Some pumps need minimum submergence. Mere fact of suction being flooded, may not yet provide "minimum submergence". Inadequate submergence can become cause for cavitation.
For volatile liquids of high vapour pressure also, just flooded suction would be inadequate NPSHa. For example, for pumps for pumping LPG or for pumps for condensate extraction, purchase specifications would often declare NPSHa = zero, implying that the pump design should be taking care of NPSHr and required margin in the design itself. The design of pumps for such applications is often made "encastre" type.
Q. What is bearing crush? how do you check bearing crush?
(Additional Information : This question was replied in Pumps India, Jan/Feb 07 issue, however we have received more information on it from Mr Rai, we are thankful to him for his contribution).
Regarding bearing crush. In this context I would like to add that this term is used for the interference of the leeve type bearings either with sphericai seating or ylindrical seating. Out side diameter of the sleeve type bearing inserts are slightly higher than the inside diameter of the bearing housing. To achieve this the diameter of the two halves at the position perpendicular to the parting plane is higher than the diameter at the position across the parting plane. This difference is termed as Bearing Crush. This serves in the following ways.
It gives tight fit of the inserts into the bearing thus preventing any movement of the bearing insert. It prevents lube oil to be filled in-between the insert and bearing housing thus better heat transfer from the bearing. To avoid the oil clearance being decreased it is of utmost importance to take oil clearance measurement after assembly.
It is written to share the information and should not be taken otherwise.
Q. We are one of the leading blood bank equipment manufactures in India. We are using a pump of 28watts,230v,50Hz single phase AC for one of our equipment. but we are frequently getting the complaints from the field especially leaking through the shaft sealants, Can you suggest me a suitable pump for our use.
28W, 230V, 50 Hz, single-phase becomes more the specification of the motor than the pump. For the pump, the specification should mention flow-rate and pressure, and also the liquid characteristics, obviously blood. Blood is a highly viscous liquid and also needs to be handled hygienically. I think a pump to handle blood hygienically should be a positive displacement pump preferably of the diaphragm type or peristaltic type, which are inherently seal-less and leak-less. This is of course a general recommendation. This can be better fine-tuned, if you would detail the flow-rate and pressure.
Q. Thank u for the valuable information the requirement is not for the use in circulation of blood. we required it for circulation of water at a temperature of 56 degree in one of our equipment called Plasma thawing bath. we want the pump spec of head 4.5M and LPH -300.
Since you had earlier mentioned about the problem of leakage with these pumps for Plasma Thawing Bath, I would recommend a pump with vertical motor. Such pump is used in circulating machine tool coolant in machine tools, such as lathes, drilling machines or CNC lathes, etc. The height to be delivered is about same as 4.5 m mentioned by you and the discharge is also of similar order as 300 lph. Pumps on machine tools also handle circulating coolant, which often could be hot after contact with metal-chips machined by the machine. As such 56 Deg C is not a very hot temperature for most common materials used in pump-construction.
Other similar pump is one, used in Desert coolers. For pumps for desert coolers, there has even been an Indian Standard IS-11951, where the pumps lifts the water from the tray in the bottom to the tray on the top, so that people can get cool breeze from the air blown by the fan across a curtain of the fragrant grass.
Pumps of machine tool coolant and of desert cooler are made by many, many people. For your application, to be free of leakage problem, they should be vertical, whereby the pump stays submerged in the hot water sump.
Hope, this helps.
Q. We Manufacture Domestic selfpriming and Centrifugal pump during the test of centrifugal pump of 1.5 hp 2 x 2 The following is the observation. Impeller OD 125 mm Pump over heated in 240 v and tripped of after running for six hour Reduced OD to II8 mm 240 v pumps is ok 220 v it tripped off after an hour Impeller OD reduced to 117 mm 240 v and 220 it is ok but tripped off at 180v we do not want to apply this method by reducing the OD of the impeller. What is the reason for the tripping off Was it required to reduce the impeller od by doing so will the performance of the pump get affected. Please advise with the solution.
Tripping off of the motor is due to overload. With regenerative turbine type impellers in domestic, self-priming centrifugal pumps, it may prove effective to try reducing the impeller width by facing from both sides and redoing the assembly maintaining the original clearances.
Q. Thanks for the reply sir, can this method applied for centrifugal agri monobloc pump, by doing facing on both the sides, Will the centre point of the vanes with the volute can be maintained pls clarify.
No. The design logic of commonplace centrifugal pumps is totally different. By the way, have you already tried facing the impeller of regenerative turbine type impeller? What percentage change in width has given what change in power? I shall be curious to learn of the trials.
Q. One of our customer using centrifugal (end suction)pump to pumping the hexane from underground tank, they have facing cavitation problem. Pipe line arranged on the top of tank. Pls, advise how to avoid the cavitation
Most effective solution would be to change over to a vertical sump pump, which will work submerged in the liquid. The pump should stay submerged even with the minimum liquid level. Such pump will eliminate suction piping, footvalve, cavitation and re-priming at every loss of prime.
Q. Kindly tell me the formula for horizontal piston pumps, available in single, double and triple pistons. how can v calculate the discharge at the pump at given pressure. for eg. a pump with suction capacity of 36 lpm and max Rpm 950. how can v calculate the discharge of pump at diffirent pressures by using their pulley sizes etc.
Discharge of a piston pump is basically (area of piston * stroke length * rpm)
Maximum Pressure = HP*k*Pump efficiency/Q/(sp. gr.)
k = constant appropriate to the units used for power and Q
For pump efficiency one shall have to consult the pump-manufacturer.
For multiplex pumps, total Q=Q per piston*no. of pistons, if their strokes are in phase.
Mostly they will NOT be in phase. Then the calculation becomes complex. Ideally one may have to make "discharge versus time" plots for each piston and derive a summation plot, keeping in mind the phase differences.
