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I have recently tested my hydraulic system for the gear. I have installed
two pressure guages on the high and low pressure circuits.I have the new
emergency extension cock, there are no visible external leaks and the
problem is very intermittent.
The gear extends and retracts in 8 to 10 seconds. On retraction the mains
lead the nose to the extent that the mains are in the well before the nose
starts to retract.
The pressure gauges show only a small increase in pressure on retraction
until the gear is fully up when the pressure rises and the pump shuts down.
The same applies on the extension cycle when the gear is fully down and
locked the low pressure rises to 700 psi and the pump shuts down. In other
words the system takes very little force to operate until the cylinders
reach their stops.
It is on the extension cycle that a very intermittent problem has surfaced.
The gear goes down and locks. The pressure builds up to 700 psig and the
pump shuts down. The low pressure starts to bleed off and it is possible to
see the high pressure gauge move off its zero position as the low pressure
drops.. The pump cuts in restores the pressure, shuts off and the cycle
begins again.
If the gear is retracted and again extended the problem disappears. It
appears as if the low pressure is leaking across to the high pressure side
but not every time. If you leave the system off overnight in the morning
there will often be 400 to 500psig left in the circuit.
So what is happening? The gauges suggest that the low pressure is migrating
to the high pressure side either across the emergency extension cock or
across the piston of one or more of the double acting cylinders. But why
not all the time? Could it be air in the system? How do you trouble shoot
an intermittent fault ? In theory I should be able to blank off the LP
pressure to the cylinders until the fault disappears but I may not get the
fault to reappear on command! Perhaps I should start with the cock.
Another probability is that I have a bubble of air somewhere.
Any ideas anyone?
Ian Crowe
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