hydraulic power pack and pump

[salih123]

I encountered the following issue when trying to run a new hydrulic pump with an existing hydrulic power pack (Variable RPM diesel).
the hydrulic power pack uses a gear pump to pump the hydrulic fluid with flow rate of 32gpm and maximum pressure of 3500psi. The hydrulic pumpend on the other hand requires a minmum pressure of 3000psi at flow rate of 8gpm. Can someone help me understand why this hydrulic pack didnt run the pump. When I run the hydrulic pack while watching the pressure gauage the pressure rises to about 700psi then the fluid would just pass right back to the hydrulic tank through the drain hose and the pressure would drop down to zero. Not sure why this is happening but could it be too much flow?

 

[hydtools]

A circuit schematic would help us help you with your problem.

Sounds like there is an unloading valve in the system.

Why are you using such a large pump? 32gpm at what rpm when you need only 8gpm?

Ted

 

[hydromech]

It's not too much flow...too much flow causes more pressure not less.

If the pressure rose to 700 PSI and then dropped to zero, it sounds like something has let go.

Where is this drain hose you are talking about?

Is the power unit driving a motor...is the drain hose coming from the motor?

Throw us a bone...something to work with to help you. A drawing would be nice.

Adrian

 

[micalbrch]

I bet the relief valve at the gear pump opens at 700 psi.

 

[hydromech]

If the relief valve opens at 700 PSI, the pressure would remain at 700 PSI, not drop to zero.

It may well be a relief and unloading valve, but even then when the pressure drops, the pump should come back onto load.

Until we see a schematic...I'm sticking with a broken part.

Rule number 1 in hydraulic system commissioning is to have the pressure control valves set to zero until you know exactly what will happen when the pressure comes on.

Adrian

 

[micalbrch]

Adrian,

Whether or not the pressure remains at 700 psi depends upon where the gauge is installed.

 

[hydromech]

Pressure gauges don't make pressure, they measure it. The location of gauge is of no consequence.

There is no point in arguing about anything, we need to see the schematic first...we are all blind until then.

 

[salih123]

Gentlemen,
thank you for the responses. Attached is a schematic of the pump controls. The reason im stating that the flow is passing right back into the hydrulic tank through the drain valve is becuase when I unpluged the drain hose connection (QD) from the pump while leaving the feed and return lines connected and turn the hyrulic pack ON, the pump actually started spinning and the hydrulic pack pressure gauge was reading 3000psi. The pump is rated for a maixmum of 4500psi.

Ted, I am not using a large pump. The pump is a 4" hydrulic sub pump and I like to run it with our existing 6" hydrulic power pack. This pump is new and its a heavy duty dredging pump that requires high pressure hydrulic pack to run it. We are trying to avoid having to buy a larger hydrulic pack specially that the hydrulic pack we own can overcome the minmium required pressure to run this pump (3000psi)

Micalbrch, pressure relief valve cannot possible open up at 700psi. the pump is rated for 4500psi max and 3000psi min.

 

[hydtools]

OK, just so I understand. You have a hydraulic power pack powering a hydraulic motor driven pump which is new. Your attached schematic shows the new hydraulic motor which drives the pump. Perhaps the new motor is plumbed in reverse and the flow is bypassing through the motor run-down check valve.

Where is your pressure gage located in the system?

Ted

 

[hydromech]

If it was as Ted says, all of the flow would go through the check valve, the motor would not rotate.

I suspect the motor piping is not correct. Either that or their is a massive leak in the motor. Taking the casing drain hose off should not make the motor turn.

The casing drain is only to remove oil that leaks out of the hydraulic system.

If we assume the power unit pump is running and oil is supplied to the motor, the motor will not turn unless the flow of oil can leave the motor. Taking off the drain hose makes the motor turn, so this is letting the oil out of the motor.

First job is to verify the piping.

 

[DubMac]

Very confusing terminology; should refer to the "new hydraulic pump" a motor since that's what it is acting as.

SO first, I would look at the new hydraulic MOTOR's curve and see just how much flow it will accept. SOunds like the 32gpm could be overwhelming it's capacity range.

As for relief valves, or popoff valves; the only type I'm familiar with are set to particular pressure and when that is exceeded, the valve opens completely up and there will be no restriction to flow; i.e. pressure will drop to zero and not remain at the set value.

Salih123, can you tell us the type of hydraulic motor you are using? Is it an axial piston type? A brand name would help.

 

[hydtools]

Salih123, if the motor was connected incorrectly to the hydraulic system and disconnecting the case drain from the motor caused pressure to increase, you may have damaged the motor shaft seal. The case drain is to provide a very low pressure return path for motor leakage and keep the shaft seal at the lowest possible pressure to not exceed the rated seal pressure.

Ted