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# 30 GPM pump vs 20 GPM pump

## 30 GPM pump vs 20 GPM pump

(OP)
I have a hydraulic power unit which is a very basic design that there can be.

A hydraulic motor is being driven by a hydraulic pump. The pump is being run by a diesel engine. There is a factory set pressure releif valve set at 1100 psi. There are regulatory , bypass and emergency shut off valves also in the circuit.

The pump flow at full capacity is 20 gpm. The gear motor needs to run at 1000 psi i.e. the inlet side of the motor is 1000 psi. The maximum allowable rpm of the engine motor is 3200 rpm. This is an existing design handed to me and claimed by everyone to be successful in the past.

The problem is that 20 gpm at 1000 psi is attainable only at 3100-3200 rpm of the engine. The hydraulic oil is heating to undesired temperature.My suggestion is to go for a 30 gpm pump. Would this bring down the engine speed and also meeting the flow rate for the specified pressure ?

### RE: 30 GPM pump vs 20 GPM pump

Sized correctly, the max flow and pressure of the pump should coincide with the peak torque of the engine.

This seems to be what you have said. At peak torque, the pump can supply 20 GPM @ 1000 PSI. If the system is as basis as you say, then  all of the energy will be transferred to heat.

For the same power from the engine, increasing the flow of the pump by 50% will mean you will have to reduce the pressure otherwise the engine will stall. You say the minimum pressure to start the hydraulic motor is 1000 PSI. This means that increasing the pump displacement will not solve the problem as you will not have enough power to run the pump.

If the power unit is getting hotter than it should, this suggests a problem with the pump setup. What sort of pump is it?

When the engine is running, if the pump is loaded, that is pressurised, it will just blow all of the oil over the relief valve. That will convert almost all of the power in the engine into heat.

For more assistance, you will need to share more details of the system...pump and valve details etc...schematic would be good too.

### RE: 30 GPM pump vs 20 GPM pump

If your problem is that the system is overheating, there are losses you must find and eliminate.  Changing to a larger pump may cause the engine to stall and will not solve the overheating problem.
Why do you say the motor needs 1000psi to run?  Motors are flow driven devices.  Pressure depends upon the load the motor is driving.  Is the motor stalled?  If so, heat is being generated by all the flow passing through the relief valve.
I would suggest your relief valve setting is too low, too close the the required running pressure.  The relief valve could be opening when the motor starts up and not resetting to closed after the motor is at speed.  Check the relief valve for proper operation; cracking pressure, full flow pressure, reset pressure.

Ted

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