Hydraulic pump cycles in flight

Submitted by billabx (Bill Sutton) on Thu, 02/10/2022 - 14:24

Forums: 

I'm am A&P working with an owner to troubleshoot a landing gear problem on his 320. With the gear retracted (on jacks or in flight) the hydraulic pump continues to cycle intermittently as pressure appears to bleed off slightly. We've tweaked the high pressure switch to no avail. I'm inclined to believe an actuator or hydraulic switch is leaking slightly. Has anyone had this issue? 

 

Thanks,

Bill

Bill

Submitted by Tom Sullivan on

Bill

A hydraulic gauge on the system would help a lot but it sounds like a leak down of some pressure so the switch is re-engaging the pump.  External leaks should be fairly easy to determine.  If not that then you may want to isolate components to see if you're getting some internal leakage on something.

Tom Sullivan

Thanks Tom. That's the theory

Submitted by billabx on

Thanks Tom. That's the theory I'm working on. No external leaks apparent. We're looking for an internal leak.

Bill,

Submitted by Tom Sullivan on

Bill,

I had a small scratch in one of the valve faces on my control valve that I repaired with 1,000 grit sand paper, after isolating most the rest of the system.  In retrospect I would have blocked the feed into the valve bank first and then worked OUT from there.  My IVPT has an accumulator and I believe ALL the models have that.  That is another item that may need to be checked.  
 

Tom

Bill,

Submitted by Tom Sullivan on

Bill,

I had a small scratch in one of the valve faces on my control valve that I repaired with 1,000 grit sand paper, after isolating most the rest of the system.  In retrospect I would have blocked the feed into the valve bank first and then worked OUT from there.  My IVPT has an accumulator and I believe ALL the models have that.  That is another item that may need to be checked.  
 

Tom

Bill, 

Submitted by shamus.allen@ya... on

Bill, 

I also am having an issue with this at the moment. In my Legacy, this is only happening in the air. Since my gear indicators only tell me that the gear is down and locked, I don't have any way of knowing if they are somehow coming slightly down under air loads, causing the hydraulic pump to cycle them back up, or if (as you eluded to a possibility of above) there's an internal leak. 

Right now I'm installing "Gear in Transit" indicators to help me with situational awareness in that regard. But I'm also inquiring with Lancair about actuator rebuild kits. 

Did you successfully figure out what the problem was? 

Shamus 

rpastusek's picture

Shamus

Submitted by rpastusek on

Shamus

The gear in your Legacy are held in the retracted position by hydraulic pressure at approximately 1000 PSI.  An adjustable pressure switch activates the pump any time the pressure drops below 950 PSI or so. An “external” hydraulic leak will dump hyd oil in the airplane or on the ground. An “internal” leak allows the fluid to pass from the pressurized side of the hydraulic system to the unpressurized return lines and back to the reservoir-no external leak. 
While “in transit” gear indicator lights are useful for SA and troubleshooting, they won’t help with the pump cycling because the pump will cycle at a pressure well above what’s required to hold the gear retracted; and it’s a leak you are looking for…
A messy and time-consuming—but better—way to find your problem is to disconnect and plug the input and output lines to each actuator and valve, one at a time, and pressurize the system. When the pump no longer cycles, you’ve found the leaky part. In most cases actuators can be repaired with new seals, available from Lancair. A check valve might require replacement. 
Hope this helps!!

Bob