First as to checking the pump pressure look up 35-530 in the manual.
Second a pump may be pumping fluid and the valve can return it to
the tank without there being very much pressure since when the
valve is set to the normal level the fluid returns to the tank
without being subject to any restriction in the valve. It is only
when the valve is set to fill that the return port is closed off
and the pump must now supply fluid at as high a pressure as is
necessary to lift the vehicle back to a level position up to a
pressure of 130-180 bar. Once the vehicle is at the correct level
the fill valve is closed off keeping the pressure in the strut
part of the system constant and at the same time opening the
return valve to route the fluid which the pump is producing back
to the tank at almost no pressure. This is to allow the power
that the engine needs to pump the fluid at high pressure to be
used for pushing the vehicle down the road and save fuel as well
as to reduce the temp of the pump and fluid. When the vehicle
gets unloaded the valve changes to lower, where both the strut
and return valves are open letting the vehicle lower to the
normal ride height. All that while the pump is still pumping
fluid but at the lowest pressure required only for circulation.
Check out 35-501 for the full working description.
So just because a pump is capable of pushing fluid at say 5 lbs
just to keep it circulating and the temp in the pump at a safe
level, does not mean it is able to pump that fluid up to the
pressure required to lift the vehicle and load up to where it
needs to be. The only way to find that out is to lift the back of
the vehicle by turning the valve to the fill position and watch
the back rise while watching the connected gauge to see how much
pressure the pump is capable of producing. If it does 130 bar
it's good to go.
Manfred
Date: Wed, 23 Apr 2014 23:37:11 -0400
From: Mitch Haley <m...@voyager.net>
Subject: Re: [MBZ] sls troubles
Andrew Strasfogel wrote:
> > Is there a way to test the pump for "sufficient pressure"?
Is this even
> > plausible? It doesn't leak and the fluid circulates. So
how is there a
> > problem?
If fluid is being returned to the filter under the reservoir cap,
I would feel
safe in concluding that the pump is forcing fluid through the
valve, and
therefore the pump isn't the problem.
Mitch.
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