Trim brake valve problems
 

My Trim brake valve behaves like a switch though it is supposed to be proportional. It is being used with Trim brake hubs. If I go into the radio programming and advance the servo just 1% of travel at a time, the brakes still just jump from nothing to fully on. Has anyone got a Trim valve and know what the problem is? Also with the valve at the "ready position" next to the braking point, the spring load is very high and the servo is struggling all the time to maintain position, does yours behave like that? The spring load is so high once into the braking zone that the servo is bouncing back and fore against it. Sometimes the valve does not feed air to the brakes but just dumps all the air from the tank out of the vent which is rather worrying when you apply the brakes and nothing happens! Have I got a duff valve or are they just not good?

H.

RE: Trim brake valve problems
 

Hi Harry

PM me your number and I'll give you a call to go through it.

Ed

RE: Trim brake valve problems
 

Your valve sounds like something inside is trashed. I have three of them and they basicly work well. I use a mini servo at 30 oz/in, and while they do need to push a little hard, it's within the servo's capacity. The servo does not struggle, bounce or rock, even at full pressure (120 psi). The servo will be pushed back when the radio is turned off if the brake was set to on. it should only dump air out the vent when the brakes are released.

I have found the best way to set up a Trim valve is with a gauge plumbed in place of the brake hub. The braking range is narrow and once past it, you can push in farther with no more effect. The gauge also helps to set the "arm" point as well. Once set up, disconnect from the gauge and plug in the brake hub.

RE: Trim brake valve problems
 

Thud_Driver,

What a GREAT idea! Man, I wish that I had thought of the pressure guage idea. I have two Trim valves and they both work well with mini-servos. I have found that the braking is "more proportional" if I keep the hub O-rings lubed with white Lithium grease.

Tailwinds,

John

RE: Trim brake valve problems
 

I followed up the idea of putting a pressure gauge on the valve output and found that it is working exactly as described in the instructions.

The problem seems to be that when that pressure arrives at the brake unit, the brakes do not behave proportionally. I had put a dab of silicon grease in the brakes to prevent snatching. The effect at the wheels is on or off, despite the valve giving a truly proportional pressure. Also, when the brakes are released the valve is supposed to give a "dragging" brake until up elevator is put in, the pressure gauge says the valve is doing that but the brakes at the wheels have released completely when the valve drops to the drag pressure. There are no leaks in the air tubes. What could be causing the brake units themselves to be acting like this?

H.

RE: Trim brake valve problems
 

Hi Harry

When you put the silicone on the brkes, did you put it on the outside of the o-ring only? If so, it sounds like the o-rings may be sticking. If so, do the folowing:
1) Remove the o-rings(best wayis to inflate them with air pressure and them roll them off the hub)
2) Clean the o-ring and the groove
3) Apply a little silicone grease to the groove
4) re-install the o-ring.

This grease application helps the o-ring slide in the groove properly and allow it to move out to apply light pressure.

Please let me know if there are any other problems.

Ed

RE: Trim brake valve problems
 

Thanks for that Ed. Yes, I had applied grease only to the outer edge of the O rings. I had wondered if the problem is the O rings sticking and taking a high pressure to make them "jump" out. If I can persuade them out of their grooves I will give it a try.

Although "white lithium grease" seems to be the norm in the USA for use on cars, it is not used here in the UK except for highly specialised industrial applications so it is not generally available. I work on the assumption that vaseline (petroleum jelly) will rot or attack the rubber of an O ring but that silicon grease is safe for rubber O rings - is that right?

thanks

Harry

RE: Trim brake valve problems
 

Hi Harry

Any time Harry.

When you remove the o-ring, be careful not to nick or cut it. You can use vaseline on these o-rings without worry. They're viton so they're impervious to most things. I prefer the silicone lubricant as it's what's specified by the o-ring manufacturer.

Good Luck,
Ed

RE: Trim brake valve problems
 

Thanks ever so much for your help guys, I now have a beautifully proportional braking system. The O rings were sticking then jumping out, I think the units have been idle for 2 to 4 years since manufacture and there was a tiny thin layer of rubber sticking on the side of the unit which was causing them to stick. They now move out and in freely. Also, using a pressure gauge to see what is really happening when setting up the radio to move the valve made that part so easy.

cheers

Harry

RE: Trim brake valve problems
 

Hi Harry

Glad to be of assistance.

Ed

RE: Trim brake valve problems
 

Dear Ed,

I have same valve for my Tomcat and your recommendation of some silicon grease to the O-ring is very helpful to me. Therefore, is there any way to have similar programing for my 9X JR instead of 10X. I have only manual for setting with 10X.

Please show me the way of best setting this nice valve.


Jai Young Shim

RE: Trim brake valve problems
 

Thud_Driver,
Great Idea!

RE: Trim brake valve problems
 

Thanks. I was going crazy trying to hit it just right and the gauge clearly showed what was going on.

RE: Trim brake valve problems
 

Hi Jai

I will see what I can find and I'll let you know. I fly Futaba, so I'm not familair with JR.

Ed

RE: Trim brake valve problems
 

Thanks for your help guys, the Sabre had its first flights today. The brakes were a bit iffy though, when they worked they worked fine and just as the valve instruction says they should work, but sometimes the system lost all pressure on the first application of the brake leaving no brakes for landing, eek.

H.