My Citroen XM 3.0 PR-Vestige

[White Exec]

Dean, how's the return (overflow/excess pressure relief) pipe from the PR back to the reservoir?
If you remove it at the reservoir end, and run the pump, when it gets up to cut-out pressure, it ought to be passing fluid back to reservoir.
If it doesn't, the pump will - I would think - be left pumping against a solid stop.

[Jan-hendrik]

how's the return

If there were a blockage in that return pipe it would just pop off at the pressure regulator side as the connection to the PRV is just with a steel band.

[White Exec]

Agree. Wasn't thinking so much that the pipe would be blocked, but that the return at the PR might not be operating.

[Dean]

The pressure regulator returns fine back to the FDV, and the pipe from the FDV back to the tank was happy to draw the contents of the tank out when disconnected so no issue there.

D

[White Exec]

390-00/2 is the best hydraulic diagram I have of the 5-piston pump working with Pressure Flow Regulator (10) ("FDV") and Pressure Regulator/Accumulator (3).

It shows the pump feeding the FDV, which feeds steering (with 80-100bar), and allows pump output to pass through to the PR/Acc., which outputs HP to suspension/brakes.

[There are thus effectively two pressure regulators taking pump output: FDV to steering (c90bar) and PR to everything else (145...170bar).]

Unwanted pump output (excess pressure) must be relieved (back to reservoir):
- on 6+2 cars, excess main system pressure is bled off directly to the reservoir

- on 5-piston cars, according to the diagram, it is fed back to the FDV, and then back to the reservoir (probably to eliminate one more return pipe to the tank)

PR obviously needs to be able to shed excess pressure.
FDV needs to do likewise......There may be no demand for HP fluid supply (PR is cut out), and steering may not be calling for fluid either.

These two thus share a return pipe back to the reservoir.
Note also, from the diagram, the steering Rotary Valve (11) also feeds into this FDV+PR return pipe.
SO....Observing that there is a flow of fluid back to the reservoir via this single pipe does not conclusively show which of the three sources of return (FDV, PR, Steering Valve) is operating.

That's how I understand it.

"The pressure regulator returns fine back to the FDV, and the pipe from the FDV back to the tank was happy to draw the contents of the tank out when disconnected so no issue there."

I'm a bit confused by this second bit. This pipe should only be returning fluid back to the tank, not drawing it out. Or could it have been siphonage out of the reservoir?

I'd advise:

Check fluid return from the PR Separate the return pipe from PR to FDV, plug the FDV hose/port, and see whether, when the pump is running and PR gets to cut-out pressure [the point when you'd expect the pump to go solid, iiuyc], the PR spits out excess fluid. If it does, good sign. If it doesn't, then pressure relief (fluid exhaust) in the PR isn't working, but blocked.

If that works ok, reconnect PR to FDV and
Check fluid return from FDV Undo the return pipe leading away from the FDV at the FDV (heading towards reservoir), and run pump up again to cut-out; this pipe/port should start issuing (more) excess fluid as soon as cut-out occurs. NB: I say 'more', because some may be coming out as the FDV relieves itself of unwanted steering fluid. If no 'more' fluid comes out, there's something in the FDV preventing the PR from shedding excess pressure.

It boils down to the pump going solid; there must be a blockage or obstacle to pressure relief.

[Dean]

Yes Chris, it was syphoning out of the tank when disconnected, i have had the pressure regulator set up with a spare 2.0i pump on the bench at i can confirm, damn that pump it hard to turn above 40 bar of pressure, i was sure this was not right so i tried it with a different pressure regulator, same thing. With both, the return was working fine.
I took a video but did not upload because it got a good shot of my arm but not what i was doing and i had the radio on and realised i would get hammered for that.

D

[Dean]

https://youtu.be/GnpqGzZ_LaQ" onclick="window.open(this.href);return false;

D

[White Exec]

I'm not following what your video is showing.
Pump coupled straight to PR, presumably.
Pump turned by hand?....and goes difficult to turn when ??? bar is indicated - on the PR output?

[Dean]

at 40bar it gets tough to turn, at 100bar it starts to get really difficult. It's a bit awkward as im trying to hold the pump with one hand and turn in with the other, this is a different pump, i tried a third pump with another regulator and it does the same thing so i have concluded this is normal operation.
I was meant to put it back together tonight but im having lazy evening, been a long day.

D

[Dieselman]

Dean,
Can you confirm your engine has the correct bolt for locking the LHM pump with the belt taught. If not, it's possible the belt tension is being relaxed, which then causes the belt to slip and smoke impressively, meanwhile shedding rubber dust. While driving this would burn the belt out in no time at all.

The bolt I bodged in to hold mie couldn't be tightened enough and even at idle managed to slacken the tension a little. Once the belt started squeaking it was smoking and shedding. There wasn't enough traction to lift the car.

Today, I've made a new bolt out of some 8mm studding with a nut welded on one end. it allows me to tighten it fully, however I might add another bit of studding sticking out at right angles, to allow a nut to be used as a tensioner as well as locking the original studding from turning.