I'm stumped. These hydraulics are killing me.

[Marlowe]

I\'m stumped. These hydraulics are killing me.

I thought I had it, but yesterday I blew another seal in my hydraulic pump on my Mitsubishi 1801. I can only get a few hours on it before it happens.

I posted earlier about the engine changing tone as if it were under a load when the 3ph is raised all the way. If I back off on it a bit, the strain is relieved. That's fine. I can put a stop on the travel to keep that from happening. But, I can't put a stop on the FEL to keep it from bottoming out, which happens most of the time when I dig into a pile of dirt. I suppose what should be happening is that a pop-off valve should come off the seat to allow the fluid to bypass when the implement bottoms out, and I suppose that the pop-off pressure should be such that damage is not done. Apparently that's not happening. What I can't seem to find though is the valve. Where would it be hiding? I've had the pump apart, but I wasn't looking for a pop-off or by-pass valve. Could it be internal? Any ideas guys, I'm going crazy here.

Thanks a bunch,

Tom

 

[slowrev]

Re: I\'m stumped. These hydraulics are killing me.

The pressure relief valve is generally external to the pump. It could be in the lift mechanism or in the loader shuttle valve assembly, or actually pretty much anywhere in the high pressure line.

Ben

 

[geneP]

Re: I\'m stumped. These hydraulics are killing me.

reducing the pop-off pressure will probably reduce the lifting capacity of your loader. I suppose it's possible someone in the past could have raised the pressure to increase capacity. It seems to me it is time to get some help, or at least a pressure guage to monitor/diagnose if you have a pressure problem. Maybe the pump has worn bearings or bushing that are wallowing out the seals. I feel for you and hope you get it straghtened out.

 

[RickB]

Re: I\'m stumped. These hydraulics are killing me.

Time to cave in and buy a manual. The relief valve definitely needs to be checked both visually and with a gauge. It probably is NOT located in the pump body, but downstream between the pump and first spool valve or within the first spool valve body. NH compacts have the main relief in the distribution block below the brake pedals ( hydro pedals on Class III). NH hitches also have an extenal follow-up linkage on the rockshaft that can be adjusted to eliminate pump bypass at the upper limit of travel. I don't know about the Mitsu's, and not a lot of others do, either. Buy a manual and learn to be an expert.

 

[Marlowe]

Re: I\'m stumped. These hydraulics are killing me.

I'd love to have a manual if I could find a source for one, but I'd want a service manual, not the owner's manual. I've got a pretty good handle on the routine maintanance outlined in an owner's manual.

What I've learned so far; It should have a pressure relief valve. It shouldn't be in the pump. It may not be the cause of my problem.

If I could determine the pressures I should be looking for I most likely could answer some of my questions regarding the relief valve. The seal itself is not literally failing; it is being blown out of its seat. I've tried two different types of sealer, both of which I've used successfully in the past. I'm confident the seal is coming out of the seat through excessive pressure. Both the FEL and the three point hitch operate as they should and hold their positions indefinitely, suggesting to me that there is no feedback to the pump that could cause the excess pressure.

One thing I've found in my search though that puzzles me still. A typical hydraulic circuit feeds the high pressure fluid to a spool valve, which basically sends the fluid where it needs to go, or sends it back to the reservoir. So far, so good, but I assume they are referring to the lever actuating the 3ph, but then they go on to say that a spool valve lever will automatically return to center when released. I've never seen any 3ph lever do that. That's what the lever on the FEL does, as I'd expect it to.

Anyway, excuse my rambling. My back's against the wall here. I've got a deadline looming on a building permit and I don't have the luxury of time. I really need this tractor to work soon or I'll have to go the rental route for site prep.

Thanks again,

Tom

 

[rberg]

Re: I\'m stumped. These hydraulics are killing me.

The shaft seals on hydraulic pumps are usually ported to the pump suction pressure so that the shaft seal is not overpressured. Sometimes this is just a small passage way from the seal chamber to the suction port. Sometimes there is a passage way from each pump port (suction and discharge) and each has a check valve in it. The check valve on the discharge end will shut off the seal from the discharge pressure and the check valve on the suction end will open to dump leakage back to the suction port. If the pump is mounted so that the discharge port is connected to the suction line and the suction port to the discharge line then the pump discharge pressure could be blowing the seal out if it is not the type with check valves. Are the suction and discharge ports the same size and can the pump be mounted either way?

 

[Marlowe]

Re: I\'m stumped. These hydraulics are killing me.

The pump can only be mounted one way, and the intake and outlet lines are not the same size, although I'm not sure about the pump's ports. I'll be taking it down in the next few minutes and look for what you've described.

Thanks

 

[BB_TX]

Re: I\'m stumped. These hydraulics are killing me.

I don't know much about hydraulic systems, but <font color="blue"> these diagrams </font> show the pressure relief valve installed on the control valve.

 

[Marlowe]

Re: I\'m stumped. These hydraulics are killing me.

Great diagrams. Thanks for the help.

I found the pressure relief valve. It was adjustable through shimming. For the sake of experimentation, I removed a few shims. I'll let you all know how this turns out. I've got my fingers crossed.

Tom

 

[jinman]

Re: I\'m stumped. These hydraulics are killing me.

Tom, on my tractor, removing shims increases pressure. You may have just gone the wrong way on pressure. You need a pressure gage that goes up to 5000 psi so you can "T" it off your hydraulic pressure side of the pump and know what pressures are blowing the seal. I have a pressure gage with a quick-attach fitting that I recently used to check my tractor's hydraulic pressure. I just plugged it into a remote valve and operated the control valve. On your tractor, you should have quick-attach fittings for your FEL that you can remove one for curl or lift and insert the pressure gage for a static check of pressure. To check dynamic pressure, you'll have to "T" into the line.