Excavator hydraulic pump help ?

[Rich B1]

Did you try blowing air through the valve to see if it open center? If it isn稚 open center, trying to make gear pumps work is going to be tough. Very tough.

 

[racerboy832]

Hi Guys it's been a while but I finally got around to checking out the flow.. I got discouraged and have too many projects.. If I take Air and blow into the three pressure lines on my pump. The air blows right into the oil tank on all 3 lines. If I then blow air into the tank side it blows air right back out of 2 of the 3 pressure sides.. I follow the one line that doesn't return from the tank, under the cap of the valve body is a check ball and a spring.. If I take it out.. Air flows both ways clearly on all directions. Now is this any open center or closed center? Can I use a dumb old gear pump? Thank you..

 

[oldnslo]

You need to verify which line is pressure line to the directional valve and confirm that pressure in the inlet of the valve flows freely to tank.

All pump lines to tank does not sound correct since the load sense line should be restricted or no flow to tank and also a small line.

 

[racerboy832]

Hi guys it’s been a while. I rebuilt the pump with new parts. It fired up and functions as it should. Before I get too far into using it I wanted to check a few things to follow up with some suggestions.

1) a couple posted that high case pressure caused a piston head pop off and that was the cause of the crash. How do I check case pressure? The case drain is plumbed into the supply side of the pump. It’s on the low side of the case but there is a place to put it in the high side where I bleed the pump before starting it.

2) I have a pressure/ Vacuum gauge on the reservoir tank. What am I looking to see psi?

3) if I had an issue with a regular on one side of the pump would that of crashed the pump?

thank you.

 

[oldnslo]

Hi guys it’s been a while. I rebuilt the pump with new parts. It fired up and functions as it should. Before I get too far into using it I wanted to check a few things to follow up with some suggestions.

1) a couple posted that high case pressure caused a piston head pop off and that was the cause of the crash. How do I check case pressure? The case drain is plumbed into the supply side of the pump. It’s on the low side of the case but there is a place to put it in the high side where I bleed the pump before starting it.

2) I have a pressure/ Vacuum gauge on the reservoir tank. What am I looking to see psi?

3) if I had an issue with a regular on one side of the pump would that of crashed the pump?

thank you.

1) typically the case drain would go directly to tank and not into the pump inlet. Reason for this is that case flow is usually the warmest oil and also potentially dirty from minuscule wear particles. The case should also be plumbed in a manner that insures the case will always stay full of oil.

2) most reservoirs run at atmospheric pressure so you should see no pressure or very little pressure while operating.

3) a bad regulator or control should not damage the pump unless pressure was so low it would not maintain the hydrodynamic bearing this is typically 120 - 150 PSI

 

[racerboy832]

When adjusting the regulator the pump shop said to adjust them so the rpms drop 200rpm before it hits the relief setting. These pumps can run up around 4000 psi but I have everything set to 3000.

I could replumb the case drain into the tank. I guess the only thing it will do it cool off the fluid. There is a suction screen but it’s not that fine to catch micro particles.

where would it of created such a vacuum to pop the heads off the last pistons? I’m trying to see if I missed something.

 

[oldnslo]

Racer
If the case pressure is approximately 5 -7 PSI higher than the inlet it can cause slippers to start lifting off which then has slipper retainer pulling on the slippers instead of holding them on the swash plate. This is especially true when the pump is changing displacement rapidly like going from feathering to full speed out of the hole.

this lift off can be a momentary thing that you will only find with good pressure transducer and data acquisition equipment, very rarely Will a gauge respond fast enough to these potential spikes.

 

[racerboy832]

I’m just trying to figure out if there is anything I can do to minimize the chance of it happening again. Both sides of the pump share the same case drain. The other side looked perfect. Is it possible the gear pump on the end leaked some pressure into the main pump? All the seals were new.

 

[oldnslo]

You state both pumps share the same case drain. Is there a hose to each pump connected externally together or just one from one pump for both pumps? I.e a common port for both cases?

What size is the case drain line versus the port size in the pump? If combining multiple pumps the line size where they combine should be larger but frequently are not.

I am just attempting to provide you with some things that might have caused your failure. A big unknown is did something score or compromise the wear surface on the failed which created excessive leakage - case flow which then contributed to the catastrophic failure? This is also a possibility but very hard to prove after the fact.

Best to do everything you can to keep system clean during assembly and then hopefully return line filters will keep the system clean.

Best wishes on keeping that unit running for years.

 

[racerboy832]

You state both pumps share the same case drain. Is there a hose to each pump connected externally together or just one from one pump for both pumps? I.e a common port for both cases?

What size is the case drain line versus the port size in the pump? If combining multiple pumps the line size where they combine should be larger but frequently are not.

I am just attempting to provide you with some things that might have caused your failure. A big unknown is did something score or compromise the wear surface on the failed which created excessive leakage - case flow which then contributed to the catastrophic failure? This is also a possibility but very hard to prove after the fact.

Best to do everything you can to keep system clean during assembly and then hopefully return line filters will keep the system clean.

Best wishes on keeping that unit running for years.

It’s has two sets of rotating groups and a gear pump. It shares a common supply which is about 2 inches in diameter. The cases themselves have an Allen plug on each. One is at 12 o’clock and one at 6 o’clock. The 6 o’clock one has the hose connected to it that acts like a case drain back to the supply side. The other side is just capped. I used this side to bleed the air out of it before starting. I have no idea how the case pressure crosses from the left to right side


the faces on the rotation groups and valve plates still looked great even after the failure.

This pump has been been pieced together by quite a few people. I’ve spent a ton of money buying pieces previous builders lost. I know the last rotation group looked good but was used.