Gear pump pressure loss

[653jon]

The Gear pump supplies barrier fluid (Oil) to a set of pumps as a part of the plan54. The set pressure of the
gear pump is 1200 psi, and it has been found that the pump losses its pressure over a period of time ?
appreciate comments on the probable scenarios?

 

[MikeHalloran]

A gear pump has some intrinsic internal leakage.

If you build up pressure in the discharge, then stop rotating the shaft, the pressure will decay, as the pumped fluid leaks back through the tooth tip clearances and the gear face clearances. This typically happens in seconds, for small pumps and small rigid downstream chambers.

A WORN OUT gear pump will have considerably larger internal leakage, and will eventually be unable to supply any given demand downstream, so the pump would "lose its pressure", hopefully over a period of years when pumping oil.

There is not nearly enough data visible here to say for sure, but it may be time to rebuild or replace your pump. ... OR your relief valve or whatever is 'set' to control the pressure, may be drifting, or worn out. ... OR there is a leak that you don't know about yet.







Mike Halloran
Pembroke Pines, FL, USA

 

[653jon]

This is relatively new and about an year old skid.The gradual decline of pressure happens over a period of a couple of months and requires readjustment.
It runs fine and again the same phenomena happens?

 

[hydtools]

What do you readjust?

Ted

 

[653jon]

I mean the pressure setting to 1200.

 

[MikeHalloran]

Uh, hydtools is trying to figure out exactly what knob you turn to adjust the pressure setting.
Is it part of the pump, or part of some other component?
Is it a setting in a PLC's HMI?

A photograph would help. A P&ID might help more.

Thanks.


Mike Halloran
Pembroke Pines, FL, USA

 

[653jon]

The pressure relief valve is not a part of the pump. It is external to the pump at the discharge line, and routed back to the oil reservoir.
It is set locally after starting the pump.

Thanks.

 

[hydtools]

So you readjust the relief valve to bring pressure up and believe the problem is the pump?

Ted

 

[653jon]

I doubt gas entrainment in the fluid, but i believe gear pumps can handle gases to a larger extent.

 

[EnergyMix]

hytools, The problem is ALWAYS the pump, didnja know ...

653jon, have you ensured there is not a leak elsewhere in your system?

Want to know the do's and don'ts of Eng-Tips? Read FAQ731-376.
English not your native language? Looking for some help in getting your question across to others or understanding their answers? Go to forum1529.

 

[Pumpsonly]

When the pressure drop , did you notice any spill back or passing of the relief valve?
Does your relief valve adjustment stem / screw has a jam/lock nut to secure the stem?
Any vibration could cause the adjustment stem of the relief valve to come loose if there is no jam / lock nut and the setting will be affected.

 

[653jon]

The relief valve has lock nut.
currently,we are planning to inspect one of the gear pumps internals.

 

[Pumpsonly]

I would suggest you inspect your relief valve first and have it tested. The phenomenon described by you looks more like the relief valve is leaking.

 

[hydromech]

If you can, put your hand on the relief valve return line. If it is hotter than the rest of the system, the relief valve is leaking. A leaking pressure relief valve will cause the oil to heat up and thin out, causing the valve to leak more...causing more heat...and so on.

It's by no means a scientific approach, by it helps to diagnose a leaky system without stripping parts out.

Better still...run the return line into a bucket and monitor what comes out. You shouldn't see any oil at all. If you do, that is the problem.

Adrian

 

[hydtools]

If the relief is being used to set and control system pressure there will be flow out of the return. Controlling pressure means it, the valve, is open. Otherwise pressure will be less than the pressure setting. If pressure in the system is falling, then there must be a leak reducing system resistance to flow or the flow rate has diminished out of the pump. Increasing fluid temperature will cause fluid viscosity to be lower and there will be a resulting reduction in flow resistance and the accompanying loss in pressure. There may also be a loss of flow rate out of the pump due to the increasing temperature and lower viscosity, i.e. more pump leakage.

Ted