Hydraulic system pressure.

[Roy Boles]

Hello everyone. I'm having a problem with the hydraulic system on my 98 Marquis. The pressure is to high and I've had to replace three filters because they have started leaking . Two of the filters were leaking at the seam, the last one ruptured from the side. Any ideas where to start looking will help.

[Mike Shumack]

Are you referring to the hyd pump for steering and engine cooling fan (or the hydraulic leveling system)?

The hydraulic pump (if like the one on my 2005) has a built in pressure relief valve. it is a spring loaded valve - the valve could be sticking. Have you put a pressure gauge on the system to know for sure the pressure is too high.

But usually the filter is on the "suction side" of the pump sop there would be no pressure there.
Are you using quality (OEM) filters?

[Roy Boles]

It is the Hyd. System for the fan and steering. No i haven't put a gauge in yet. Evidently the filter is on the pressure side of the system. I spoke to BCS and they said that flow could be reversed. He said he's seen that before.

[Mike Shumack]

I found this diagram (not exactly what we have since our coaches dont have a microprocessor controlled fan) but probably close. It shows the filter located on the return side of the fan motor.
According to the Beaver manual, the high side pressure can reach 130 bar (2,000 psi) under load (like when the Steering wheel is being turned), and the return line (return to tank) pressure is around 6 to 8 bar (100 psi).

You could put a gauge on the filter housing and test this. 100 psi is not too much for a filter (think oil filter pressure, where engine oil press normally runs 50 to 100 psi when cold). I have an oil filter now that is rated for up to 200 psi. but some of the chaper filter may not be able to take as much pressure (especially if something is wrong and your getting much more pressure).

The Donaldson filter (LHA SPE 15-10 equivalent) has a working pressure of 150 psi and a burst pressure of 375 psi. https://www.donaldson.com/en-us/engine/filters/products/hydraulics/assemblies/sp15-25/  So I would test that your filter is in the "workign range" of 150 psi or less.

[Roy Boles]

Thanks for the reply. I had a talk with a bus and fire truck  mechanic. I also have a rear wheel seal leaking. He said that it is probably the filter more than anything else.