The hydraulic pump in my 360 started to "burp" (ie, run for an instant) in flight more than the usual once every 20-30 minutes or so.  I could see the High side (UP) pressure going down, forcing the pump to run for an instant to repressurize the system.  After a short period where the problem went away, it then returned, with the pump cycling much too often (about every couple of minutes).  There was no evidence of an External leak and the Low side held pressure fairly well.

 

As my gear retract cylinders were about 10year old Matcos, that I have rebuilt at least once, I decided to install new cylinders now made by Wohlsenholm, who reportedly makes high quality components.  I also replaced the original gear door cylinders with new ones (I had already installed the heavy duty dump valve).

 

Now, the system would hold Low pressure for days, something it would never do before.  But, the Hi side problem was unchanged.  I disassembled the hydraulic pump and found a torn O-Ring on the Hi Side check valve (#8) on the attached drawing.  After replacing all the hydraulic pump seals, the pump did not burp at all on a 20 minute test flight.

 

One more LNC2 gear data point.

 

Regards,

Clark Baker

LNC2 360, 710hrs TT