Frequently Asked Question-26
- By Jayesh Patel
- Published 01/31/2010
Tech Quest
Turbo Driven Boiler feed Pump
We have installed electronic governor on Turbo driven boiler feed water pumps so as control speed with reference to varying boiler feed water load. What is the recommended operating speed range within which, we can operate the unit without vibration problem. Turbine/Pump normal operating speed is 12090/2983 r.p.m.
The speed range will be specific to a given rotating element, i.e. load-diagram, moments of inertia of the rotating masses, locations of bearings, etc. One needs to find the "critical speed" and avoid also its harmonics.
I want to know the steps taken in a pumping system to attain the desired operating point for the system when
(a) the pump is driven by a fixed speed motor and,
(b) when the pump is driven by either a variable speed motor or a turbine.
The operating point is the point of intersection between the H-Q curve of the pump with the H-Q curve of the system. Once a pump is set into a system, this will happen automatically. But if the operating point, which happens automatically is not the 'desired' operating point, one has to modify either the pump curve or the system curve.
There are two ways to modify the pump curve -
1) Change the speed of the pump
2) Change the diameter of the impeller of the pump
3) The system curve can be notified by modifying the system. This is usually done either by changing the setting of the delivery valve or one can change it also by revamping the system by changing the pipe-sizes and/or layout of the piping.
4) If the suction conditions in the system are prone to cause the pump to cavitate, modifying the system to eliminate cavitation will also modify the pump curve from a cavitating condition to non-cavitating condition.
5) For changing the speed of the pump (option 1 above), changing the driver from an electric motor to a turbine will often become changing from a low-speed driver to high-speed driver.
Such change is possible even by using a gearing or pulley mechanism between the pump and the motor. But at increased speed the pump demands higher power input. So, it becomes important to check whether the motor has adequate margin in power. No such caution is needed if "desired" operating point is obtainable by reducing the speed.
For determining the required speed at the "desired" operating point, say
(Q",H")one needs to find the point (Qo, Ho) on the pump curve H = a*Q^2 + b*Q + c which also is a point on the parabola through the origin and (Q", H"). The equation of this parabola will be H = k*Q^2, where k = H"/(Q")^2.
Since (Qo, Ho) is to be a point both on
H = k*Q^2 and H = a*Q^2 + b*Q + c
to find (Qo, Ho) one needs to solve the quadratic (a-k)*(Qo)^2 + b*Qo + c = 0
Actually all the mathematics starts with knowing the values of the co-efficients a, b, c for the pump curve H = a*Q^2 + b*Q + c This is not difficult, if one knows three points on the curve, say, (0, Hso), (Q1, H1) and (Q2, H2) and solves simultaneous equations. A simpler way to do this is to plot the pump curve in an Excel spreadsheet and fit a 'trendline', setting also the option for the display of the equation of the polymonial of degree 2.
Submersible pump
Vs Turbine Pump
In our Municipal Corporation for raw, water pumping for 64 mtr head and discharge 1250 m3/hr capacity, we are considering procurement multistage (2 or 3 stages) turbine type pumps.
For the some application, one of pump manufacturer has very strongly recommended single stage submersible pump with motor submerge in the water.
This being is critical application, we request the views of your technical expert Mr Abhyankar, in respect of the following parameter, with respective above two alternative.
1. Efficiency of single stage pump with respective multistage turbine pump.
2. Bearing radial and axial thrust and bearing life.
3. Track record for similar application for above duty point else where in India of single stage submersible pump.
4. Your technical advise.
5. Cost comparison.
Basically, you are looking for pumping 1250 m3/hr of raw water across a total head of 64 m. The question raised by them is whether they should opt for vertical Turbine Pumps, which are quite common in municipal water supply pumping or venture into a single-stage submersible pump.
One thing to be always borne in mind by a pump user should be to consider the overall efficiency of the pumpset, inclusive of the motor efficiency. A pump user pays for energy consumed, which is influenced by the overall efficiency. By this consideration alone a submersible pump would get ruled out, because a submersible motor can never have an efficiency compatible with that of a surface motor.
A submersible pump would also need greater depth of the sump, in turn more excavation, so higher initial cost of constructing the pumping system.
If space is not a major constraint, I would also like them to check with another option of using horizontal split casing pumps. If one can have a dry pit alongside of the sump, priming of the pumps would also not be a problem. Maintenance activity is definitely very comfortable with these pumps, far more comfortable than with VT pumps.
The suggestions about checking construction costs, energy costs and maintenance really summarize into doing a Life Cycle Cost Analysis and take all possible options into account instead of restricting the thought process to one or the other type of pump at the planning stage.
This question I found in one of the IIT question paper. I could not get to the roots of the answer. We have a centrifugal pump with a 400 lpm capacity & 32 mtr. Head. An urgent requirement arises which need 500 lpm capacity with 50 mtr. Head. Without changing impeller, what are
The options available to meet this requirement? One option is to Change motor, what are the other supportive options available?
This is an important question, please give early reply,
The ratio of discharges, 500 lpm / 400 lpm is 1.25.
The ratio of heads 50m / 32m is 1.5625, which is square of 1.25.
Obviously the question is based on affinity laws, which are similar for change in diameter or rpm.
So another option to change in diameter is change in rpm, to 1.25 times higher speed,
MOC for Abrasion & Corrosion
I would like to know the difference between abrasion and corrosion. What type of M.O.C for impeller and shaft is suitable for abrasion and corrosion?
Also let me know the selection parameters for Impeller and shaft M.O.C.
One commonplace example of understanding the difference is water laden with sand. Sand, per se, is not corrosive, but it is very abrasive. Conversely acid with no entrained solids, clear acid, will not be abrasive but highly corrosive. Sea will also be corrosive. But corrosion due to sea water is due to its alkalinity whereas corrosiveness of acids is acidic in nature. MOC for corrosion resistance has to take into consideration whether the corrosiveness is acidic or alkaline.
Abrasion is also of two types. Abrasion due to fly ash in power stations will be from fine particles moving too close to the surfaces and abrading the surfaces. Abrasion due to sand particles or coal particles will be due to the particles hitting hard on the surface and bouncing back and hitting repeatedly. This is rather erosion than abrasion. So nature of abrasive wear depends upon the angle of incidence of the particles w.r.t. the surface. Usually hard surfaces would take abrasive wear better and resilient surfaces such as elastomer-linings would take the erosive wear better. But this is too much of a thumb rule. One needs to study the wear patterns and refer to the data available in handbooks.
Utility of Mechanical Seal?
I would like to know the basic criteria for choosing Mechanical Seal in place of gland packing.
Basically it will be cost-benefit analysis. The benefits have to also take into account benefits of environmental considerations. Where the leakages are likely to be hazardous, even safety considerations become important. For example, for radioactive leakages, even mechanical seals would not give adequate sealing. One may have to adopt zero-leak constructions as available in canned motor pumps or magnetically coupled pumps.
A golden mean between commonplace gland packing and mechanical seal is also available in the style of "injectable sealants", claiming the leakage sealing being as good as the mechanical seals and installation being as simple as rope packing.
Some people also offer a hydro-dynamic sealing with an expeller impeller at the back of the centrifugal impeller. The expeller impeller expels the leakage back into the pump and does not allow leakage to emit into the atmosphere.
Mechanical seals and injectable sealants claim to be bringing down also the energy consumption. That also should be a point in the cost-benefit analysis.
So, shaft-sealing has really become a multiple choice option.
Velocity triangle for Impeller
Here I am with two basic questions,
Q. Can I know what is velocity triangle for Impeller?
Q. What is its significance in the performance of the pump?
Waiting for your valuable response.
The questions would be of interest to anybody interested in pumps.
There are two prominent velocity triangles with centrifugal impellers one at the inlet and the other at the outlet. The flow is supposed to be travelling radially from inlet to outside diameter. This direction is similar to the line of longitude on the spherical surface of the globe, from one pole to another. Hence the direction is called as the meridional direction and the velocity is called as the meridional velocity. Next, inherent to the whirling of the impeller there is the circumferential velocity at every point on the blade. There would be a relative velocity between these two velocities. So the triangle brings forth the three vectors in relation to each other. The cross-section of the passage between the two blades and the layout of the blade causes the triangle to affect the vectors at every point along the blade. So there are virtually infinite number of triangles. But for a net result one would focus primarily on the inlet and outlet triangles. Yet, the layout of the blade and the total length of the blade will also vary depending upon how the angle between the relative velocity and whirling velocity, usually called as the angle Beta, is varied from its value at inlet to its value at outlet. Longer the length of the blade there will be better "Guidance" of the flow between two blades. At the same time, longer the length, the vane passage friction will be higher. So the trick is in striking the golden mean between guidance and friction. Obviously the pump-performance will be substantially influenced by how the trick is handled. That is why, it is always said, pump design is quite an art than just theory.
Also sir requesting you for a case study or material which explains about the meridional direction and meridional velocity.
Meridional velocities are assumed in the design procedure as outlined by Pfleiderer and Stepanoff. The notation for meridional velocity is Cm' for inlet and Cm" at outlet. Mr. Stepanoff in fact put forth empirical equations as Cm' = k' *sqrt(2gH) and Cm" = k"*sqrt(2gH) and put forth curves for recommended values of k' and k" vis-a-vis design specific speed.
1. What is the difference between centrifugal & Axial pumps?
2. In what way MOC selection criteria for casing and Impeller will be depended?
3. How to check the clearance between casing and impeller?
1. What is the difference between centrifugal & Axial pumps?
Axial flow pumps are one type of centrifugal pumps. specific speed in metric units will be >75
2. In what way MOC selection criteria for casing and Impeller will be depended?
Major consideration will be corrosion-resistance. For impeller, there will be also the consideration of cavitation-resistance and maximum whirling speed. Another consideration for impeller is of manufacturing feasibiity. This consideration is also relevant for casing. But with impeller the intricacy is more critical, especially for castability.
3. How to check the clearance between casing and impeller?
I would feel a fit from a tolerance of d11 on hub of impeller and D11 I on ID of wearing ring would be appropriate. I am writing this from memory. Please check whether this would work well.
How to determine Minimum stable continuous flow & Minimum thermal continuous flow. Is there any standard which explains about these parameters & the determination in detail
Minimum stable continuous flow is to be read on such H-Q curve which is unstable. In unstable characteristics, Hmax is greater than Hso (Head at shut-off). In such case, Minimum stable continuous flow will be where a horizontal thru' Hso will intersect the H-Q curve of the pump.
Minimal thermal continuous flow is that flow, when the liquid will experience churning caused by internal re-circulation. This happens because, the cross-sections of the hydraulic passages prove to be too large for the amount of flow to be carried. The designer designs the passages ideally for the design flow. At flows less than the design flow, the passages are not ideal. This is also one reason for the drop in efficiency at flows different from design flow. The effect becomes accentuated at flows less than Minimum thermal continuous flow. Churning of the liquid causes temperature of the liquid to also rise. This in turn raises the vapour pressure of the liquid. In turn the available NPSH gets affected. By all these considerations the curve for NPSHr v/s Q becomes uncertain. So, manufacturers show NPSHr curve only ahead from Minimum thermal continuous flow.
Obviously both Minimum stable continuous flow and Minimum thermal continuous flow are to be recommended by the manufacturer and cannot be obtained from standards.
In API-610 one finds a mention of continuously rising characteristics, that means a stable characteristics, i.e. where Hmax is only at shut-off. To be more mathematically correct, for a stable characteristics, the point of maxima is not in the first quadrant.
We have centrifugal pump having capacity of 60 m3/hr and we face problem of priming. we want to put self priming chamber. the suction pipe line length is 4 meter and have 80 mm diameter. can you suggest chamber size or formula to count same?
Volume of priming chamber should be about 7 times the of the suction pipe. Higher volume is helpful for to happen as much faster.
Yield of Borewell
What does it mean that a bore having 2 inches or 3 inches of yield. Please send us the chart.
Yield of bore coloquially called as 2" flow or 3" flow implies rates of flow usually experienced with pipes of these sizes. Technically speaking the rate of flow would be area*velocity. For a given pipe size as 2" or 3 " one would get different values of flow-rates for different velocities. I guess the colloquial talk assumes an average velocity of 3m/s. I need to cross-check whether this is okay.
Re-using Oil
We have 800 Ltrs. Used gear oil. Can we reusing the same after Filtration or other way you suggest.?
Please suggest & send Information for Re-Using of Gear Oil.
Reprocessing of used gear oil is a technology by itself. One needs to check whether the contaminants have affected the chemistry of the oil and the corrosiveness of the changed chemistry, apart from the lubricity and viscosity of the oil. The reprocessing will have to redeem the oil to original chemistry viscosity, lubricity, etc. Filtration alone may not do that.
Turbo Driven Boiler feed Pump
We have installed electronic governor on Turbo driven boiler feed water pumps so as control speed with reference to varying boiler feed water load. What is the recommended operating speed range within which, we can operate the unit without vibration problem. Turbine/Pump normal operating speed is 12090/2983 r.p.m.
The speed range will be specific to a given rotating element, i.e. load-diagram, moments of inertia of the rotating masses, locations of bearings, etc. One needs to find the "critical speed" and avoid also its harmonics.
I want to know the steps taken in a pumping system to attain the desired operating point for the system when
(a) the pump is driven by a fixed speed motor and,
(b) when the pump is driven by either a variable speed motor or a turbine.
The operating point is the point of intersection between the H-Q curve of the pump with the H-Q curve of the system. Once a pump is set into a system, this will happen automatically. But if the operating point, which happens automatically is not the 'desired' operating point, one has to modify either the pump curve or the system curve.
There are two ways to modify the pump curve -
1) Change the speed of the pump
2) Change the diameter of the impeller of the pump
3) The system curve can be notified by modifying the system. This is usually done either by changing the setting of the delivery valve or one can change it also by revamping the system by changing the pipe-sizes and/or layout of the piping.
4) If the suction conditions in the system are prone to cause the pump to cavitate, modifying the system to eliminate cavitation will also modify the pump curve from a cavitating condition to non-cavitating condition.
5) For changing the speed of the pump (option 1 above), changing the driver from an electric motor to a turbine will often become changing from a low-speed driver to high-speed driver.
Such change is possible even by using a gearing or pulley mechanism between the pump and the motor. But at increased speed the pump demands higher power input. So, it becomes important to check whether the motor has adequate margin in power. No such caution is needed if "desired" operating point is obtainable by reducing the speed.
For determining the required speed at the "desired" operating point, say
(Q",H")one needs to find the point (Qo, Ho) on the pump curve H = a*Q^2 + b*Q + c which also is a point on the parabola through the origin and (Q", H"). The equation of this parabola will be H = k*Q^2, where k = H"/(Q")^2.
Since (Qo, Ho) is to be a point both on
H = k*Q^2 and H = a*Q^2 + b*Q + c
to find (Qo, Ho) one needs to solve the quadratic (a-k)*(Qo)^2 + b*Qo + c = 0
Actually all the mathematics starts with knowing the values of the co-efficients a, b, c for the pump curve H = a*Q^2 + b*Q + c This is not difficult, if one knows three points on the curve, say, (0, Hso), (Q1, H1) and (Q2, H2) and solves simultaneous equations. A simpler way to do this is to plot the pump curve in an Excel spreadsheet and fit a 'trendline', setting also the option for the display of the equation of the polymonial of degree 2.
Submersible pump
Vs Turbine Pump
In our Municipal Corporation for raw, water pumping for 64 mtr head and discharge 1250 m3/hr capacity, we are considering procurement multistage (2 or 3 stages) turbine type pumps.
For the some application, one of pump manufacturer has very strongly recommended single stage submersible pump with motor submerge in the water.
This being is critical application, we request the views of your technical expert Mr Abhyankar, in respect of the following parameter, with respective above two alternative.
1. Efficiency of single stage pump with respective multistage turbine pump.
2. Bearing radial and axial thrust and bearing life.
3. Track record for similar application for above duty point else where in India of single stage submersible pump.
4. Your technical advise.
5. Cost comparison.
Basically, you are looking for pumping 1250 m3/hr of raw water across a total head of 64 m. The question raised by them is whether they should opt for vertical Turbine Pumps, which are quite common in municipal water supply pumping or venture into a single-stage submersible pump.
One thing to be always borne in mind by a pump user should be to consider the overall efficiency of the pumpset, inclusive of the motor efficiency. A pump user pays for energy consumed, which is influenced by the overall efficiency. By this consideration alone a submersible pump would get ruled out, because a submersible motor can never have an efficiency compatible with that of a surface motor.
A submersible pump would also need greater depth of the sump, in turn more excavation, so higher initial cost of constructing the pumping system.
If space is not a major constraint, I would also like them to check with another option of using horizontal split casing pumps. If one can have a dry pit alongside of the sump, priming of the pumps would also not be a problem. Maintenance activity is definitely very comfortable with these pumps, far more comfortable than with VT pumps.
The suggestions about checking construction costs, energy costs and maintenance really summarize into doing a Life Cycle Cost Analysis and take all possible options into account instead of restricting the thought process to one or the other type of pump at the planning stage.
This question I found in one of the IIT question paper. I could not get to the roots of the answer. We have a centrifugal pump with a 400 lpm capacity & 32 mtr. Head. An urgent requirement arises which need 500 lpm capacity with 50 mtr. Head. Without changing impeller, what are
The options available to meet this requirement? One option is to Change motor, what are the other supportive options available?
This is an important question, please give early reply,
The ratio of discharges, 500 lpm / 400 lpm is 1.25.
The ratio of heads 50m / 32m is 1.5625, which is square of 1.25.
Obviously the question is based on affinity laws, which are similar for change in diameter or rpm.
So another option to change in diameter is change in rpm, to 1.25 times higher speed,
MOC for Abrasion & Corrosion
I would like to know the difference between abrasion and corrosion. What type of M.O.C for impeller and shaft is suitable for abrasion and corrosion?
Also let me know the selection parameters for Impeller and shaft M.O.C.
One commonplace example of understanding the difference is water laden with sand. Sand, per se, is not corrosive, but it is very abrasive. Conversely acid with no entrained solids, clear acid, will not be abrasive but highly corrosive. Sea will also be corrosive. But corrosion due to sea water is due to its alkalinity whereas corrosiveness of acids is acidic in nature. MOC for corrosion resistance has to take into consideration whether the corrosiveness is acidic or alkaline.
Abrasion is also of two types. Abrasion due to fly ash in power stations will be from fine particles moving too close to the surfaces and abrading the surfaces. Abrasion due to sand particles or coal particles will be due to the particles hitting hard on the surface and bouncing back and hitting repeatedly. This is rather erosion than abrasion. So nature of abrasive wear depends upon the angle of incidence of the particles w.r.t. the surface. Usually hard surfaces would take abrasive wear better and resilient surfaces such as elastomer-linings would take the erosive wear better. But this is too much of a thumb rule. One needs to study the wear patterns and refer to the data available in handbooks.
Utility of Mechanical Seal?
I would like to know the basic criteria for choosing Mechanical Seal in place of gland packing.
Basically it will be cost-benefit analysis. The benefits have to also take into account benefits of environmental considerations. Where the leakages are likely to be hazardous, even safety considerations become important. For example, for radioactive leakages, even mechanical seals would not give adequate sealing. One may have to adopt zero-leak constructions as available in canned motor pumps or magnetically coupled pumps.
A golden mean between commonplace gland packing and mechanical seal is also available in the style of "injectable sealants", claiming the leakage sealing being as good as the mechanical seals and installation being as simple as rope packing.
Some people also offer a hydro-dynamic sealing with an expeller impeller at the back of the centrifugal impeller. The expeller impeller expels the leakage back into the pump and does not allow leakage to emit into the atmosphere.
Mechanical seals and injectable sealants claim to be bringing down also the energy consumption. That also should be a point in the cost-benefit analysis.
So, shaft-sealing has really become a multiple choice option.
Velocity triangle for Impeller
Here I am with two basic questions,
Q. Can I know what is velocity triangle for Impeller?
Q. What is its significance in the performance of the pump?
Waiting for your valuable response.
The questions would be of interest to anybody interested in pumps.
There are two prominent velocity triangles with centrifugal impellers one at the inlet and the other at the outlet. The flow is supposed to be travelling radially from inlet to outside diameter. This direction is similar to the line of longitude on the spherical surface of the globe, from one pole to another. Hence the direction is called as the meridional direction and the velocity is called as the meridional velocity. Next, inherent to the whirling of the impeller there is the circumferential velocity at every point on the blade. There would be a relative velocity between these two velocities. So the triangle brings forth the three vectors in relation to each other. The cross-section of the passage between the two blades and the layout of the blade causes the triangle to affect the vectors at every point along the blade. So there are virtually infinite number of triangles. But for a net result one would focus primarily on the inlet and outlet triangles. Yet, the layout of the blade and the total length of the blade will also vary depending upon how the angle between the relative velocity and whirling velocity, usually called as the angle Beta, is varied from its value at inlet to its value at outlet. Longer the length of the blade there will be better "Guidance" of the flow between two blades. At the same time, longer the length, the vane passage friction will be higher. So the trick is in striking the golden mean between guidance and friction. Obviously the pump-performance will be substantially influenced by how the trick is handled. That is why, it is always said, pump design is quite an art than just theory.
Also sir requesting you for a case study or material which explains about the meridional direction and meridional velocity.
Meridional velocities are assumed in the design procedure as outlined by Pfleiderer and Stepanoff. The notation for meridional velocity is Cm' for inlet and Cm" at outlet. Mr. Stepanoff in fact put forth empirical equations as Cm' = k' *sqrt(2gH) and Cm" = k"*sqrt(2gH) and put forth curves for recommended values of k' and k" vis-a-vis design specific speed.
1. What is the difference between centrifugal & Axial pumps?
2. In what way MOC selection criteria for casing and Impeller will be depended?
3. How to check the clearance between casing and impeller?
1. What is the difference between centrifugal & Axial pumps?
Axial flow pumps are one type of centrifugal pumps. specific speed in metric units will be >75
2. In what way MOC selection criteria for casing and Impeller will be depended?
Major consideration will be corrosion-resistance. For impeller, there will be also the consideration of cavitation-resistance and maximum whirling speed. Another consideration for impeller is of manufacturing feasibiity. This consideration is also relevant for casing. But with impeller the intricacy is more critical, especially for castability.
3. How to check the clearance between casing and impeller?
I would feel a fit from a tolerance of d11 on hub of impeller and D11 I on ID of wearing ring would be appropriate. I am writing this from memory. Please check whether this would work well.
How to determine Minimum stable continuous flow & Minimum thermal continuous flow. Is there any standard which explains about these parameters & the determination in detail
Minimum stable continuous flow is to be read on such H-Q curve which is unstable. In unstable characteristics, Hmax is greater than Hso (Head at shut-off). In such case, Minimum stable continuous flow will be where a horizontal thru' Hso will intersect the H-Q curve of the pump.
Minimal thermal continuous flow is that flow, when the liquid will experience churning caused by internal re-circulation. This happens because, the cross-sections of the hydraulic passages prove to be too large for the amount of flow to be carried. The designer designs the passages ideally for the design flow. At flows less than the design flow, the passages are not ideal. This is also one reason for the drop in efficiency at flows different from design flow. The effect becomes accentuated at flows less than Minimum thermal continuous flow. Churning of the liquid causes temperature of the liquid to also rise. This in turn raises the vapour pressure of the liquid. In turn the available NPSH gets affected. By all these considerations the curve for NPSHr v/s Q becomes uncertain. So, manufacturers show NPSHr curve only ahead from Minimum thermal continuous flow.
Obviously both Minimum stable continuous flow and Minimum thermal continuous flow are to be recommended by the manufacturer and cannot be obtained from standards.
In API-610 one finds a mention of continuously rising characteristics, that means a stable characteristics, i.e. where Hmax is only at shut-off. To be more mathematically correct, for a stable characteristics, the point of maxima is not in the first quadrant.
We have centrifugal pump having capacity of 60 m3/hr and we face problem of priming. we want to put self priming chamber. the suction pipe line length is 4 meter and have 80 mm diameter. can you suggest chamber size or formula to count same?
Volume of priming chamber should be about 7 times the of the suction pipe. Higher volume is helpful for to happen as much faster.
Yield of Borewell
What does it mean that a bore having 2 inches or 3 inches of yield. Please send us the chart.
Yield of bore coloquially called as 2" flow or 3" flow implies rates of flow usually experienced with pipes of these sizes. Technically speaking the rate of flow would be area*velocity. For a given pipe size as 2" or 3 " one would get different values of flow-rates for different velocities. I guess the colloquial talk assumes an average velocity of 3m/s. I need to cross-check whether this is okay.
Re-using Oil
We have 800 Ltrs. Used gear oil. Can we reusing the same after Filtration or other way you suggest.?
Please suggest & send Information for Re-Using of Gear Oil.
Reprocessing of used gear oil is a technology by itself. One needs to check whether the contaminants have affected the chemistry of the oil and the corrosiveness of the changed chemistry, apart from the lubricity and viscosity of the oil. The reprocessing will have to redeem the oil to original chemistry viscosity, lubricity, etc. Filtration alone may not do that.
