Non RV question, landing gear

[pilotea]

Hi

I do have an RV6 so i dare to post about another aircraft type.... I have a Glasair 3 with a problem I am trying to solve. It's with the landing gear.

On the extend side the pressure in the hydraulic system drops very quickly. it extends the gear, pressure is then just under1000 PSI as it should be, but almost immidiately the pressure drops and the pump therefore kicks in again, then the pressure reaches the 1000 psi, pressure drops again and pump kicks in, this happens every 2 seconds. It seems like I might have a leak, but that is not the case as there are no leaks anywhere, could this be air in the system that causes this? Pump works ok and if retracting the gear, the pressure remains steady, its only on the extend side this happens.

I have a manual override that can turn the pump on, it will pump the extend side to 1300 psi, it drops with about 100 PSI/second. Any ideas?

[John-G]

Originally Posted by pilotea

I have a manual override that can turn the pump on, it will pump the extend side to 1300 psi, it drops with about 100 PSI/second. Any ideas?

I'll begin by saying I have no hands on experience with your landing gear ... but the first thing that came to mind is that the check valves inside the pump unit must be allowing hydraulic fluid to leak back into the fluid reservoir.

Being curious, I ran into this which seems to address your issue directly:
http://glasairaviation.com/wp-conten.../07/GSB127.pdf

Based on the above documentation, I think it is time to inspect/clean the check valves in the pump and look into the filters mentioned.

Hopefully others will have more detailed hands on advice for you to follow.

[BobTurner]

Most hydraulic systems are designed to move as fast as the pump can pump fluid in. e.g., once activated, the pump should not go off. It sounds like the fluid is being restricted, resulting in a pressure build up at the pump, and susequently going over the high pressure cut-off. I would look for restrictions to flow: kinked lines, clogged filters, that sort of thing.

[snopercod]

Originally Posted by pilotea

...almost immediately the pressure drops and the pump therefore kicks in again, then the pressure reaches the 1000 psi, pressure drops again and pump kicks in

You have a leak, son. Since you didn't mention loss of hydraulic fluid, the most likely place is the piston O-ring seal in one of your hydraulic cylinders leaking from the low side to the high side. Sadly, the only way to determine which of the three is leaking is to isolate them one at a time. Those cylinders are very easy to rebuild. Another less likely possibility is the hydraulic power pack itself.