Hydraulic Pressure Gauge and Pressure Reading Test

[Beltzington]

Hello I am rebuilding an old Morbark 12" wood-chipper and after replacing the engine I found an issue with the hydraulics. The two feed rollers turn forward and reverse when the control valve is activated but stall when even a small limb is fed into the rollers.

Called Morbark technical support (Excellent Customer Service) and he recommended checking the pump pressure which specs from 2000 2400 psi. It just so happened I have a 5000 psi liquid filled pressure gauge on my pressure washer and it of all wonders fit into a tap connecting the high pressure side of the pump into the control valve.

With everything running I see no deflection on the pressure meter, maybe 50psi but I think that may be my imagination. I would think that more pressure would be required to turn the feed roller motors even when not loaded as there is obviously some flow. This leads me to believe maybe my pressure gauge is not working although it works fine on the pressure washer. I also speculated the pressure relief on the valve could be stuck open but again I would expect some reading change on the meter when I cycled from forward and reverse.

So do I trust my test setup and replace the pump or is there something else I should be checking? This is my first involvement with hydraulics and I am enjoying learning how it works. As always, your help is appreciated.

 

[dfkrug]

Without any load, your gauge should read very low, and 50psi may be about right.
Note that a 5000psi gauge will not be very accurate at the extremes of its range.

To see any deflection in the meter, you need a load. So stick a small branch into
the rollers and see what the gauge says.

 

[J_J]

Pressure is developed by the load on the motor or cyl.

Your relief valve could be stuck open.

Are you sure your pump is OK.

Could your feed roller motors be worn out, and fluid is just flowing through the hyd motor?

If your pump is good and you jam a log into the feed rollers, you will see some pressure.

Is there a separate pump for the feed rollers?

 

[Beltzington]

No load, no pressure, interesting - I have been doing allot of reading recently about hydraulics and that bulb never came on. Makes perfect since in retrospect as the tank is not pressurized. If the rain holds out for a couple hours I will test tonight.

No idea how many hours are on the chipper, any or all parts could be worn-out.

The tech support guy at Morbark keeps referencing an adjustment for the pressure relieve valve but I sure can't find it. Any hints? I have all sorts of helpful pictures but have lost the capability to upload them.

Thanks!

 

[J_J]

When a hyd component stalls, you should see max pressure.

When a hyd motor is stopped by load/force, the fluid is blocked and the relief valve will try and protect the pump.

Can you show picture of the feeder valve.

 

[Beltzington]

Have not checked under load, ran out of diesel, but here are a couple pics of the control valve. Top hose is pressure side of the single pump, bottom hose returns directly to the tank, middle two hoses go to the two feed motors in series. Valve in reverses motors valve out they turn forward. Do not see any place to adjust the pressure relieve, what am I missing?

 

[SSdoxie]

Looks like the relief would be under the top hex cap at rear of the valve, just above the larger spool spring cap. There may be adjusting screw under the cap, or it could be shim type (add or remove shims as needed).

 

[Beltzington]

Well there may be the problem, I removed the cap and fluid poured out, best guess without letting it drain out was it was an open port into the valve. Looks like I may need a parts break-down of the valve.

 

[oldnslo]

Dumb question but... are you sure the gauge is connected to the pressure galley of the valve? I couldn't tell from the pictures where you had the gauge installed in reference to the inlet. Just wondering if you could have possibly installed the gauge in port that could be used for power beyond and in your system that would be common to tank.

 

[SSdoxie]

Dumb question but... are you sure the gauge is connected to the pressure galley of the valve? I couldn't tell from the pictures where you had the gauge installed in reference to the inlet. Just wondering if you could have possibly installed the gauge in port that could be used for power beyond and in your system that would be common to tank.

I had same thought at first, looking at pic a little closer it "looks" like the gauge is screwed into top of the hose fitting of hose coming from pump to the valve. If so that should give him working system pressure.