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Randy Snar in his just posted comments has hit the
nail on the head. The spool in the hydraulic pump does not always stay at the
end point of it's travel and when it doesn't, and since there is no accumulator
in the system, the fluid volume is trapped and heat will cause thermal expansion
opening the pressure switches. If you don't experience a large temperature rise
and the spool in your pump stays where it's supposed to, you won't see the
problem. So as Randy stated, if both switches trip, nothing works except opening
a fitting to relieve the pressure. Installing a "dump" valve that vents both
sides to the reservoir instead of the standard of just equalizing between both
sides will fix the problem but still requires pilot intervention after the
re-plumbing. But how many people are ready to
re-plumb their hydraulics to implement that fix ?
There is nothing in the pump except o-ring friction
to keep the spool in it's needed end position. Vibration can move it trapping
the fluid volumes. Activating the pump will force the spool back into it's end
position relieving the offending pressure and all is well with the world.
Problem is the pressure switch is open preventing the pump from activating.
Forcing the pump to activate when both switches are open will do the trick.
My electric module does exactly that . . . . automatically . . . . without
pilot intervention. It connects to both pressure switches and forces the pump to
activate in the direction selected by the gear switch if both pressure switches
are open.
Wolfgang
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