I am trying to install a gear valve on my latest jet, i have the standard blue robart valve, it leaks rapidly past the o-rings on the plunger until it bleeds to about 50 or 60 lbs and then looses air at a slower pace, all air will be lost within 15 minutes and the gear wont come down after about 5... So, i pulled a new RED vairiable robart valve from my gear kit for a P-51 i am building and installed it. SAME THING, leaks to about 50 lbs and then slows down, the air never quits leaking.. Russ

I've got the red one from Robart and it works. However, trying to trim the needle valves was a pain. So I fixed them in place and put Loctite on the thread and then used some SMC one-touch fittings w/ a adjustible knob to better control the air flow. Anyway, check the side load on the shaft and see if you can keep the air from leaking out. Try it without the servo attached and double check the tube input/outputs.

Apply some Parker O-Ring Lube to the o-rings. They might be too dry to seal.
If that fails, get a BVM Hi-Flow valve.

Harley Condra
BVM REP
JetCat REP

Is it possible it is not the retract valve that is leaking, but another part of the system?? It just with two bad vavlves in a row, maybe it's not them?? Just thought I'd ask.

Harley, get down here in November!!

I dont think you have a problem with either of the valves. I think the problem is one of your retract cylinders is allowing air past the O ring. The reason why its doing what its doing is that the air is getting past the O ring and coming back down the other pipe and then coming out the robart valve as this pipe is not sealed when the valve is in that possition. To check this, clip some forceps on each line in turn untill you find the offending cylinder.

Jason

Most common problem with the Robart valves is that you should not allow the servos to push against or over the end points of the valve.
This was a very frequent problem with our early kit builders (SpiderJets F-16) ; problems were solved when we mentioned it clearly in the manuals.

Best Regards,
Nicolas.

The valves still leak even when i have no servo hooked up to them, i should have specified that in my original post, i have also tried BVM thin oil and even changed the o-rings in the blue one, i can HEAR the leak comming out at the valve plunger.. As for the bad gear cylander, That is a possibility but would it still do it in Both postions, up and down? if so we may be on to something? Also what would i do to fix the cylander? Russ

I'm betting that Jason is right, its not the valve that is leaking, its an O ring in one (or more) of the gear cylinders that is letting air "blow by" from the high pressure side to the low pressure side. Remember, the retract valve has to exhaust air out of the low pressure side, so the leaking air will ultimately be coming out of the retract valve - even though the retract valve is not at fault. I've never had a retract valve have a really big leak that lets out all of the air quickly, but almost every retract system I've installed has had a "blow by" leak when the system is first exercized. You should take the air line off of all of the cylinders and inject some of the BVM thin oil into each one. Move the gear back and forth slowly after the oil is in there to spread it around. Then reconnect the air lines and try it out. It may take overnight for the oil to make the O rings "swell" enough to completely seal in the cylinder...

Bob

I recently had the same problem with a blue Robart and tried everything to fix it. I switched to one of those "cheap" valves and it works perfect.
V..

By gosh you were right, Apologies to Robart, i crimped off the down side of the nose gear and the leak almost stopped completley, crimped off the up side and it did stop. Now i guess i will try to fix the nose gear, You say thin oil first and then what?

YAY!! I got one!

JC,
I’m assuming also that the ENTIRE retract system is hooked up (plugged in). I found out that testing the valve without the air cylinders connected to valve, it will leak down. Even if both the retract air line and the extend lines are connected together. At first I thought I had a bad valve, before hooking up all air cylinders. I’m using the Red Robart valve and have had no problems. Hope this helps.

i have had the same problem check all your cylinders most likly it will be a o ring on a cylinder . i too thought it was the valve but it was'nt. i used soapy water in a squirt botle to locate the problem after that thw system would hold air for over a week. good luck
Arden

It will if the bore is scored at one end. Clamp the tubes.

J

Only by 56 seconds

J

You can use neumatic tool oil to seal the cylinder leak. Get it at any hardware store. Much cheaper than BVM thin oil and was the original fix before bvm started selling it. IMO Bvm thin oil is the same as neumatic tool oil.

Thin silicone shock oil for model cars is the same stuff too/

It is more than likely Blow By a cylinder piston seal. Remove the lines and add air to one end of the cylinder and pit the other end on a glass of water,
do it both ways. till you fine the one blowing bubbles. It will take while but you will have to do this or you will never get to the bottom of your problem.

They don't come much smarter than our Jason!! You could posibly find the air leaking past the cylinder rod and the piston, I've had this.

m

My bet is crossed lines, the up line is dumping into the down line...somewhere...

too bad valves in a row??? not likely.

Put the thin oil in the cylinders (both sides if you can) and work it back and forth. Then pump up the gear and operate it. You may have to manually move the gear to each position until the leak seals. Even so, once all of the gear are at the correct up or down (and locked) position, the leak should stop (if it doesn't, you may have another problem). Keep operating the gear back and forth until they go all the way on their own. Once at that point, run them through an addition 20 cycles or so. Eventually, the oil will cause the O rings to swell and the operation of the gear will seat them, and the leak should stop. I've had some gear that kept leaking with cylinder "blow by" for what seemed like forever (BVM KingCat gear, oddly enough), but eventually, the O rings seated and they worked fine.

Once you have the problem fixed, if the gear sits in one position for a period of time, it may reoccur. Also, if you have your gear slowed down with a restrictor or having the needle valve on the gear valve closed down, the problem will be harder to get rid of. Basically, as the piston travels down the cylinder, if there is any place where it doesn't fit snuggly into the cylinder, it can stop there and start to leak. It almost always seals completely when it gets to the end of the throw. That's why I always have my gear set to move as fast as possible. Some guys like them to be slow because its more "scale like," which is true, but you almost never can see the gear actually move during the cycle because the airplane is climbing away and is also fairly far away when the gear goes up. However, you can ALWAYS see the half-retracted gear sticking down and the resulting belly landing on the runway. Better to have them "slam" up and down reliably than get stuck half way...

Bob

Yes, around one of the gear cylinders as described above...

I went ahead and put thin oil in all three gears, with the offending one liberally, i have worked it and will let it set up overnite to see if it stopped the leak.. If it does not, i guess you can put a new o-ring inside the cylander if i can find the right size. Russ

Russ,

Try it now and see if it stops the leak. The oil itself is often enough to make it stop enough to get the gear moving. Then you can put some cycles on it and get it to start seating.

You can replace the O rings on some gear, but generally, they are a pain to take apart... At that point, I'd be inclined to sent them back and get the manufacturer to fix them. Who's gear is it?

Bob

Well, the problem is solved, the thin oil helped but did not stop the leak. I took the retract apart removed the cylander and opened it up, oiled and cleaned the oring manualy, still , no joy [&o]. So i removed the o-ring and simply flipped it around 180.. This worked, the leak is totaly gone now. I dont know why flipping it would make a difference but it did.. If the leak ever comes back i will just go and get new orings at the hardware store..Now i can put the test flight on the plane.. Thanks Russ