I am posting this pump question here because it seems the "PUMP ENGINEERING" forum mostly concerns itself with centrifugal pumps.

What could cause pump cavitation at low shaft speed only?

Explanation -  We have a booster pump (fixed displacement, axial piston type) which supplies the inlet of an HP pump (pressure compensated variable displacement axial piston type). Both pumps are driven off the same shaft by a diesel engine (and in fact, both pumps are integrated within a single housing!).   The boost pump circuit filters and circulates through a cooler to temper the fluid before it reaches the HP pump inlet. The booster system pressure is set by a relief valve tuned to 50 psi at shaft speed of 2500 RPM.  During operation, shaft RPM is constant at 2500 RPM.  During idle the shaft speed is reduced to about 1000 RPM. At this low speed condition, cavitation like noise is heard and it is believed to occur in the booster pump, but at high speed, all is well.

I had a couple of ideas and questions,  but little ability to go through trial and error solutions:
1 How will the booster pump relief valve behave if instead of setting it for 50 psi at 2500 RPM, we set it to 50 psi at 1000 RPM.  Could this make any difference? 
2. If case leakage was excessive, could the booster pump be starving the HP pump and maybe the HP pump is really the one that is cavitating?  Is case leakage ever likely to be higher at low shaft speed  than at higher shaft speed?
3. How would clogged case drain filters or check valves affect cavitation behavior i have described?  

What could cause cavitation at low speed only?

It has nothing to do about little digs, Bud.  We have names for our components and terminology we use in hydraulics.  The terminology and component names relate to the function of the components.  We have marketing people at the factory, and people like you that call the same component different names, it is no wonder we have a communication problem with customers.

Examples:  Motion control valve, over-center valve, really it is a counter balance valve.
Booster pump, charge pump, correct terminology is charge pump.
Dump valve, pressure limiter valve, really it is a relief valve.

Here is the game, XYZ Company has a motion control valve, ZYX Company has a counter balance valve, XYZ companies valve is much better because it controls motion, thus the name motion control must be better because the factory say’s it is.

A dump valve works much better than a relief valve, because it dumps the pressure and not just relieves it.  By the way, this is the sign you see when you pull your camper up to a site to dump tour toilet.

It is hard enough to communicate with customers without hearing that my “thing won’t shift”, or “my dump valve” is making noise.  Or how about “that shinny round thing will not go in and out fast enough”.  It is like some people call a reservoir a tank, two entirely different things.

Booster pump implies that a pump is raising the pressure from one level to another level, boosting.  A charge pump implies that it is used to charge or keep full with flow and pressure a closed loop circuit.
Just because some idiot at Denison does not know the difference, does not mean we do not.

So it is not about hurting Buds feelings or throwing digs, it’s about a CFPE helping to dumb down our industry and making communication that much harder.  I have no apology in trying to keep the standards higher, not lower.

It has nothing to do about little digs, Bud.  We have names for our components and terminology we use in hydraulics.  The terminology and component names relate to the function of the components.  We have marketing people at the factory, and people like you that call the same component different names, it is no wonder we have a communication problem with customers.

Examples:  Motion control valve, over-center valve, really it is a counter balance valve.
Booster pump, charge pump, correct terminology is charge pump.
Dump valve, pressure limiter valve, really it is a relief valve.

Here is the game, XYZ Company has a motion control valve, ZYX Company has a counter balance valve, XYZ companies valve is much better because it controls motion, thus the name motion control must be better because the factory say’s it is.

A dump valve works much better than a relief valve, because it dumps the pressure and not just relieves it.  By the way, this is the sign you see when you pull your camper up to a site to dump tour toilet.

It is hard enough to communicate with customers without hearing that my “thing won’t shift”, or “my dump valve” is making noise.  Or how about “that shinny round thing will not go in and out fast enough”.  It is like some people call a reservoir a tank, two entirely different things.

Booster pump implies that a pump is raising the pressure from one level to another level, boosting.  A charge pump implies that it is used to charge or keep full with flow and pressure a closed loop circuit.
Just because some idiot at Denison does not know the difference, does not mean we do not.

So it is not about hurting Buds feelings or throwing digs, it’s about a CFPE helping to dumb down our industry and making communication that much harder.  I have no apology in trying to keep the standards higher, not lower.

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