Weak hydraulics- bad pump or relief valve

[sony224422]

1964 ford 4000 gas

So I guess from the beginning- I bought the tractor not running and got it running and ru well. I used the front loader to move some small amounts of dirt, and nothing really heavy. I tried the backhoe and it wouldnt dig. It could barely get the teeth to cut in. So I went to the backhoe relief and it was almost all the way screwed down. So I put a pressure gauge on the dipper cylinder and could build 1400 psi.

I then disconnected the feed out of the loader control for the backhoe and return off the filter housing for the backhoe to remove that from the system, and add in my otc tester.

My tester measured the flow and psi above hooked up that way.

When I think back, Im pretty sure if I pulled the backhoe up it would bog the engine a bit and Id hear the relief. The front end loader could not lift the front off the ground more than a few inches either and I think I heard that squeal too. Is there a part number for the relief to replace it with? I do not seem to be able to find one. My books show a break down but no numbers

I have isolated my backhoe (723) and gone through the controls for the controls for the loader with a flow meter and my pump makes good pressure until the psi is increased. At idle with no load, my pump will be in 10-13 gpm range. At 1600 rpm its over 20, but as the psi hit around 1200, the flow dropped to under 5. It dropped the gpm as the psi increased. There is not really an easy way to isolate the pump, I cant get a connection off the pump or the connection to the controls without taking off every line.

 

[oldnslo]

Does the flow drop suddenly at a given pressure or does it drop steadily as the pressure is increased from min to max?

If suddenly at a given consistent pressure I would suspect a relief opening. If flows decreases steadily from min pressure to max then I would suspect a leak path or failing pump.

when doing your testing do you hear anything than sounds like oil spraying or flowing through a restriction? Any area of loader valve get hot quicker than rest of the system? That much flow loss at pressure is going to create heat so hot spot would be a place to investigate. Same with pump if exposed it will get hot quickly if leaking internally.

 

[rScotty]

1964 ford 4000 gas

So I guess from the beginning- I bought the tractor not running and got it running and ru well. I used the front loader to move some small amounts of dirt, and nothing really heavy. I tried the backhoe and it wouldnt dig. It could barely get the teeth to cut in. So I went to the backhoe relief and it was almost all the way screwed down. So I put a pressure gauge on the dipper cylinder and could build 1400 psi.

I then disconnected the feed out of the loader control for the backhoe and return off the filter housing for the backhoe to remove that from the system, and add in my otc tester.

My tester measured the flow and psi above hooked up that way.

When I think back, Im pretty sure if I pulled the backhoe up it would bog the engine a bit and Id hear the relief. The front end loader could not lift the front off the ground more than a few inches either and I think I heard that squeal too. Is there a part number for the relief to replace it with? I do not seem to be able to find one. My books show a break down but no numbers

I have isolated my backhoe (723) and gone through the controls for the controls for the loader with a flow meter and my pump makes good pressure until the psi is increased. At idle with no load, my pump will be in 10-13 gpm range. At 1600 rpm its over 20, but as the psi hit around 1200, the flow dropped to under 5. It dropped the gpm as the psi increased. There is not really an easy way to isolate the pump, I cant get a connection off the pump or the connection to the controls without taking off every line.

I'm assuming that this is an open center hydraulic system.... but not sure. Let me know if it isn't. I don't have much experience with closed center systems.

To start off, some of those older open center hydraulic systems didn't use as high of a pressure as the modern tractors run. Today everything seems to be over 2200psi and 3000 is common. But the older machines from 50 years ago did a lot of their work at 1000 to 1500 psi. It's not uncommon on vintage machines to find the relief set at 1200 to 1500 psi.

Check your specs in a workshop manual. Since you have a flowmeter - btw, congratulations on that tool, many shops don't have one. Anyway, you know that GPM will fall as PSI rises. Then falls off a cliff when the relief valve opens. There should be a chart for that in the workshop manual.

From what you are seeing I'd take that relief valve apart and see where the problem is. But I sure wouldn't run it without a relief valve in the system. If you disable the existing relief valve, can you add another one in series with it for protection?
rScotty

 

[sony224422]

Thank you- it is open spool. The book calls for 21.5 gpm and a 2000 psi pressure. It’s hard to find parts for, it’s an old Cessna control, the relief valves are discontinued, but I don’t know if I take it out and bring it to a shop if they would be able to find the right replacement. It is a cartridge style so I don’t think there’s much I can do towards cleaning it.

I am thinking it’s more the pump, but I plan today to set everything back up and let it run for a little and see if the pump gets hot from leaking or if the relief does. I’m hoping that will lead me in the right direction.

I am also hoping a shop can rebuild that pump as it seems to be one of a lot that could possibly fit, but new would require modifications

 

[rScotty]

Did you try putting your flowmeter in the return line that goes from the relief valve to the sump? If the problem is the relief valve hanging open that should show up as some pressure and a lot of flow in a line that normally should not have much of either.

The other thing you might want to check is how the power steering is fed. Some of them are fed by an adjustable proportional flow "Y" valve which takes a percentage of the main hydraulic flow and will not allow flow to anywhere else until it's own flow demand is satisfied. So it is possible in those types of circuits for the power steering to rob all the flow - using what they need and dumping the rest back to the sump. The power steering will also have its own relief valve, and that can go bad too.

You may be able to block off the power steering to check that. Or put the flowmeter in the power steering line.

SAFETY! Always be super cautious and suspicious when anything (like a flowmeter) puts pressure on any return line. It is fairly common for return lines to have a lower pressure rating and lower pressure fittings than pressure feed lines. The return lines from any relief valve should be able to handle full system pressure, but you never know.
A flowmeter puts a variable restriction in the line it is measuring and that always causes the psi to rise.

 

[rScotty]

I am also hoping a shop can rebuild that pump as it seems to be one of a lot that could possibly fit, but new would require modifications

If it comes to a pump rebuild, I wonder if a PTO-driven pump could be plumbed into the existing system and then just bypass the engine driven pump. Surplus Center.com has 20GPM in the $450 range. I've done that to run a 3pt backhoe but never an entire system.

 

[sony224422]

I am going to work on getting pump off. Unfortunately this tractor doesn’t have a pto, being a backhoe it must not have been an option.
The power steering is off a different pump, but that was a good thought. After watching the gpm steadily fall as pressure increased, and then have full flow with no pressure, I’m pretty sure the pump is leaking by. I believe it is a commercial shearing P25 so I hope I can have it rebuilt

 

[rScotty]

I am going to work on getting pump off. Unfortunately this tractor doesn’t have a pto, being a backhoe it must not have been an option.
The power steering is off a different pump, but that was a good thought. After watching the gpm steadily fall as pressure increased, and then have full flow with no pressure, I’m pretty sure the pump is leaking by. I believe it is a commercial shearing P25 so I hope I can have it rebuilt

It wouldn't surprise me to find that pump, parts, or even a new bolt on replacement. Just looking around I found a nice general trade manual showing typical Parker parts at:

https://www.hydropower.nl/PumpsCI.pdf

If you do find a pump rebuilder others might be interested.