You’re about to embark on some real time consuming fun. If you have one of the old dump valves, they were rated at only about 600 psi as I recall. The ball valve had a Teflon coating that would deform under high pressure and leak. You need a Parker valve rated at 2000 psi or higher. I believe mine is rated at 5000 psi. But, if your dump valve is that hard to get to, maybe you want to check all your gear and door cylinders first. There are six of them so get a handful of AN fitting caps & plugs, jack up your plane and have at it. I’d also suggest installing 2 hydraulic 3000 psi pressure gauges, one on the low pressure side, another on the high side. Cap & plug all of the cylinders, isolate the valve from the pump and then run the pump. If it cycles, the pump has an internal leak. If not, introduce the valve back into the system and run it again. If it cycles, your valve is bad. Then introduce one cylinder at a time, run the pump and see when it cycles. This all takes a lot of time but it’s the only way to figure it out. Happy hunting.
Danny
LNC2-360 Mk-II
Nothing is foolproof to the sufficiently talented fool.
From: Erik Larson [mailto:asw20747@aol.com]
Sent: Friday, June 28, 2013 9:32 AM
To: lml@lancaironline.net
Subject: [LML] Fwd: Hydraulic pump cycling / Replacing dump valve
I have a Legacy, 6 1/2 years, appx 650 hours, we started experiencing momentary hydraulic pump cycling, averaging now every 6-8 minutes for a micro second.
There are NO external leaks and NO loss of fluid in the system, so I guess it's time to start trouble shooting to find the internal bypass. Following some previous postings on the issue, it seems that if it's not the cylinders, then the next logical place would be the dump valve.
At first glance it looks like getting the dump valve changed out could be quite a job. Anyone that's done it recently care to share some Helpful Hints?
It looks like the only way to get to it, is by disassembling the throttle quadrant, even then it looks tight?
Any advise on that or general trouble shooting advise for the hydraulic system would be GREATLY appreciated!