Power steering pump has back pressure.

[COASTBUSTER]

I have a Ford 4000 series Industrial series tractor. After using it the Eaton steering pump vents a lot of air and fluid. Eventually it runs out of fluid and the steering wont turn under power. Why so much back pressure in the reservoir? Just recently had the pump rebuilt but it did this before the rebuild also. Any ideas. Dan :cool2:

 

[J_J]

You probably have a suction leak in the pump, plus the fluid expands when hot.

So the combination of air bubbles and hot fluid causes your overflow.

Do you see air bubbles in the fluid.

Any back pressure would be caused by a restriction in the return flow path.

 

[COASTBUSTER]

I'll check for suction leak but everything seems tight and no leaks from any hoses. Possibly a crack in the pump somewhere that expands when hot and under pressure. This pump has always,since I've owned the tractor, done this. Steering worked when I first acquired the machine. Then stopped. I took the pump apart figuring that as the culprit. I found the pressure relief valve was upside down. Put it in correctly but steering (whatever was left of the steering) seemed to work better with the valve upside down. Reinstalled it that way and went on to find 2 broken centering springs in the control valve were broken in half. Replaced them and steering works 90% better.While doing the control valve I sent the pump to a rebuilder. I'm wondering if he reninstalled the pressure relief valve upside down thinking that thats the way he disassembled the pump and put it back together wrong. Only an inspection and disassembly of the pump will determine that I guess. Any other thoughts J_J ?

 

[J_J]

I think it would be hard to mess up the relief valve position as the end of the seat is shaped to the base of the valve body. Are both ends of the relief valve poppet the same?

Also look at the load check valves.

Do you have relief valves on your boom cyl that might be leaking?

What about boom drop after shut off?

 

[COASTBUSTER]

I don't remember if the ends of the valve are the same. Did it some time ago. But I do remember that it will fit in either way. I have to disassemble the pump to check. Secondly I'm not familiar with load check valves. Is this for the steering or boom question? Thirdly, I'm also not familiar with the relief valves on the boom cylinder. I've just recently started to explore the problem. And fourth,the boom drops in any condition. Dan

 

[J_J]

Most all valves have load check valves to prevent the load dropping when shifting the spool.

They are usually in between the spool work ports. Usually a spring and seat.

It also prevents the fluid from passing back to the IN port.

Excerpt

Diagnosing Cylinder Drift
Therefore, while the root cause of the problem in both examples is the leaking piston seal, the physics is fundamentally different from the general belief. And if the theory is understood, a pressure gauge can be a useful tool for establishing the cause of cylinder drift.

In either of these examples, if the cylinder is drifting but there is no equalization of pressure across the piston seal, the directional control valve or load control valve is the source of the problem.

So in essence, if the two hyd gauges show the same pressure, the cyl has equalized and no further movement.

Another question, would how much move of the rod for the cyl to equalize.

Now, if the load still drops, then you can assume the spools are leaking, and you could see this if the return hose was removed, by the leaking fluid flowing out the return port.

These are just some observations on my part, and some of you may think differently.

 

[COASTBUSTER]

Took the pump apart today. Flow control/relief valve is installed correctly. Inside of this valve is a ball,spring and ball seat. Should I be able to compress the ball and spring using a pin punch? I've tried but it won't budge. The spring doesn't look that heavy duty. I even tapped it with the punch and ball peen but still won't budge. The book says it's supposed to unseat at 800 lbs of pressure. Here's a pic of the valve.NEW Holland Power Steering Hydraulic Valve 501 601 801 1871 2030 2130 86534520 | eBay

 

[COASTBUSTER]

Problem fixed. Went to a friend mechanic friend who recommended another guy who he calls GOD. The guy,Chris looked at the flow valve and said the ball is not supposed to move. It is just pressed in there as a stop to keep the spring from falling out and that there is another ball at the other end of the spring that you can't see inside the valve. Said he wouldn't buy another,this one will work fine. He said polish it with crocus cloth and reinstall. A new valve is $220. Only paid $700 for the whole tractor. He said air was getting in the system. I told him there was no way. Every connection was tight. He said all of these pumps do this,just use the tractor and turn the wheels to their full stop position a few times and any air will evacuate. Did that and it works like new. Also the flow valve was sticking a little until I crocus clothed it. Now I don't hear any bubbling and have no spillover. Thank you J_J for your insight. I also have a dump truck that I want to install a separate reservoir on to fill the lift piston,so I have some questions as to which side of the piston is the low pressure return. I think it's probably the side with the fill hole which is on the bottom of the piston anchored to the frame. Piston seal leaks but it's easier and cheaper to just put in a res. which I have already and just add 30w to it. Rarely use the truck but every year when I do,I have to use the backhoe bucket to raise the dump body and fill the piston. Thanks again.

 

[COASTBUSTER]

Adding a hydraulic reservoir to an 83 chev c64 dump truck This says it all.