hydraulic pump cycling

04-13-2011, 12:50 AM

mike reibing | hydraulic pump cycling

I have noticed my hydraulic pump cycling every minute or so lately when in flight with the gear up. It seems to be something leaking internally with the manifold block with all the solenoids on them. It seems to be the one that is in charge when the gear is up. Has anyone else experienced this and if so what did you do to fix it? Does anyone have a drawing of what the internals of that manifold block looks like?


04-13-2011, 10:48 PM

keithw | Hyd Pump Cycl

Hi Mike I have had this same problem from time to time but here are a few things that I have done. 1) When I was building the plane Dick Silva wrote about the time that on a long flight his system ran out of oil for what reason I dont know, but when he landed he found that the heat from running all the time had melted the plastic reseivor and he thought he was very close to a fire. 2) This incident got my attention !!!!!!!! Dick had no way of knowing that the pump was running!!!!!!!!!!!!!! So my solution was a yellow caution light directly in front of me in on the panel. Result = I know when it is on and also aware of the cycling. 3) I wanted to have the ability to shut it off in flight so I installed a switch on the panel. 4) With the aid of an pressure gage I can monitor in flight the pressure at any time. 5) I started out with the (Gernade) accumulator. Yes alot of cycling. Then S N A came out with a large accumulator which I bought and installed. Wow I thought this was just the cats meow. Wrong!!!! The diaphram burst and the volume of oil was so great that it emptied the reservoir and the pump ran constanly. I put the (Gernade) back on and have used it ever scince (400 hrs plus) Note at some times it cycles very little and times alot. If it does alot piss on it I just shut It off. Ha Ha it gets kind of exciting when on landing and the gear won't come down. I quickly realize the prob---Turn the pump back on. After this long disertation there is a new valving system that is suppose to be better??????? You may have it in your plane already. Geo. liked the best. Call PlaneMakers. John can help. Happy flying! See you at the splash in and the AirVenture Race Keith Walljasper N80CC

04-14-2011, 08:44 PM

Ed Lynch | Hyd pump cycling

Mike, Check that your accumulator has about 900 psi air charge. If it has lost its charge, that will cause pump cycling. Most FBOs have a nitrogen tank to charge accumulators, struts and the like. Ed

04-15-2011, 01:32 PM



When you go to check the charge in the accumulator, turn off the hydraulic pump and run the flaps up and down to bleed off the pressure in the system. Then check the pressure.

John J

04-16-2011, 05:59 PM

Tom Saccio | Nose wheel Steering

My nose wheel steering which is hydraulic turns on its own. When the power is turned on the wheel turns to the right with out me pressing the button. Any ideas would be helpful. There is 950 lbs in the granade and the hydraulic pressure is reading about 1550 lbs. If I tried to put less pressure the wheels will not go up.

Tom Saccio

04-17-2011, 05:03 PM

mike reibing | hydraulic problems

With all the olio problems I have had I went out and purchased a nitrogen tank. So I have already set the charge in the accumulator to 900 and it didn't make any difference. I am thinking it is some foreign material stuck in this big valve body with all the solenoids attached. The pressure only bleeds off when the gear are up and with tapping on the side of the valve body it increased the cycle time from 20 seconds to about 90 seconds. Unfortunately it didn’t fix it completely.

Tom, I think you could be having the same problem, because a year ago mine did the same thing on two different occasions. Both times it was while I was taxing and it was a son of a bitch to stay out of the rhubarb. I’m sure the controllers had a good laugh seeing me do donuts on the taxi way. After fighting with it for a while it stopped. So I think something that was stuck in the system moved on. Right after that I install a new hydraulic return tank. Mine was full of cracks and you would not believe the crap in it. So that is why I think my problems are from crap in the hydraulic system sticking in that valve body. I'm hoping someone have a drawing so I don't have to wing it.

John, do you know where the valve body came from?

Mike Reibling

04-18-2011, 08:09 AM


Mike and Tom;

The valves are made by Wandfluh:


They even have Dick's Seawind on their home page.

You both have flaps, gear, and steering so you have the "full" system. If you have 12 solenoids, then you have the newer system. I'm almost possitive that Mike has that. If you have six solenoids then you have the older system. I think you have that Tom. I'm not sure.

I think all the valve bodies have a rough schematic on their sides.

I agree with you Mike. I'm pretty sure all those problems could be crud in the system.

I hope this helps,

John J

04-18-2011, 08:20 PM

Ed Lynch | cycling hyd pump

I had a problem early on with what turned out to be an aluminum chip hanging up the gear "up" valve. After a brief phone conversation with Wand fluh, they told me to send back the gear manifold, and they cleaned and repaired it very reasonably. Remove and refit the manifolds is straightforward, but tedious. Ed