OT Home made Backhoe Revisited Again

DrLarryE · Oct 26, 2014

I have asked several questions about this backhoe before, and each time I think it's the last time, but I really hope this is it. I have replaced the pump and it all works well now except that the engine will quickly stall when a cylinder reaches the end of it's stroke. When I say quickly, I mean there is not enough time to let up on the control to prevent it. Since the pump is moving oil any time it is operating, and it will run while I am not operating a cylinder it must have a functioning relief valve, right? Should that same valve relieve the pressure when I reach the end of a cylinder? Would an easy (and reasonably correct) solution be to put a relief valve just before the controls that would run the oil back into the tank and adjust the pressure to the point that the engine struggles but doesn't stall right away?

Mike Hearth · Oct 26, 2014

I think there is a valve stuck in your control. Should go to bypass at end of stroke.

Bob · Oct 26, 2014

While the oil is simply circulating through the valve, the relief valve isn't opening.

When you move the valve lever and the cylinder reaches the end of it's stroke, the relief valve has to quickly open to give the flow of oil a place to go.

Your relief valve is not functioning, is set too high, you have a valve WITHOUT a relief valve built in, or you have plumbed the valve backwards, reversing the inlet and tank/return ports.

DrLarryE · Oct 26, 2014

So the relief valve would probably be located on the input side of the controls and when the relief valve is activated, it would divert the oil to the same pathway that it is traveling when no cylinder is activated. (I'm basing it's location on what looks like a relief valve in that position.) It has sat unused for a long time, and when I got it running the pump needed replacing because it pumped poorly, so that's why it didn't stall prior to replacing the pump, right?

Bob · Oct 26, 2014

See if the relief is stuck.

Is it adjustable?

Sometimes, there's a tag marked with the factory setting. If it's a fixed relief cartridge it MAY be stamped with pressure setting #.

old · Oct 26, 2014

You also may have a valve body that does not have a relief valve built in. Had that on my 841 years ago and boy did it cause problem with 2 new pumps a dealer installed. Both pumps the center plate exploded on

OT Home made Backhoe Revisited Again

DrLarryE

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Mike Hearth

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Bob

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DrLarryE

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Bob

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old

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