REFLECTOR: Low Hydraulic Pressure or Pump Check Valve Leaking?

[Laurence Coen]

Bob,

I think Rene' has the answer.  If the emergency gear down valve is moved toward the dump position it will produce the symptoms you described.  I had a case that was similar that was cured by tightening the packing nut around the dump valve shaft.  In my case the only effect was the pump cycled once every 30 seconds.

Larry Coen
N136LC


From: Bob Jackson 
Sent: Tuesday, August 09, 2011 11:37 PM
To: 'Velocity Aircraft Owners and Builders list' 
Subject: REFLECTOR: Low Hydraulic Pressure or Pump Check Valve Leaking?


I'm stuck in Vernal UT after flying from Orlando, heading for Oregon.  After take-off from Vernal on the third and last leg to Portland, I got an unsafe gear up light.  After returning and investigating (no problem getting the gear back down), I noticed the hydraulic reservoir was down more than a third of the way from the top (we normally keep our fluid level (with the gear down) about ½" from the top of the reservoir.  I refilled the reservoir and tried again.  This time I noticed the pump (light) was cycling even on the ground, and got the same 'Unsafe UP' light indication after take-off.

 

Does anyone have an ideas or suggestions?  I assume that the pump can't create enough UP pressure because the up-side pressure relief valve won't let it.

 

Attached is a PDF copy of the Mercruiser Outdrive Maintenance manual - pg 20 has a good diagram of the internal design of (our) gear pump, including shuttle valve, pressure relief valves, etc.  Can anyone explain:

  1.. why the pump's tank level is different for the Gear UP and Gear DOWN directions (isn't there the same amount of fluid on both sides of the pistons?) 
  2.. if you've ever seen a situation where the both the UP and the DOWN sides get pressurized so that neither pressure switch will any longer allow you to change the gear's position (different problem from mine in Vernal, but just asking since I heard of it once)? 
  3.. What could cause my hydraulic reservoir to go down by 1/3 during just the first two legs from Orlando, when it's never gone down rapidly like that before.  We don't seem to have any big leaks in the overall hydraulic plumbing that I've been able to find yet. 
  4.. Is there any way for the hydraulic pump or reservoir to 'vent' fluid, other than from bad hydraulic connections that are external to it? 
 

Thanks for the help,

Bob Jackson

N2XF



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