Problem With Air Valve?

[damnyankee36]

I noticed on my system with an Accu-air manifold, that when I release the pressure in the tanks, my bags loose pressure. With the tanks empty, the line pressure is low enough that I can remove the main airline to the manifold. Air then starts coming out of the "IN" port of the manifold.

Is this right? Since the tank normally has more pressure than the bags, I would imagine this would never cause a problem. I just thought the only time air should be moving is when either the lift valve or the dump valve is opened.

Maybe I need to see if there is trash in the valves even though I have a filter/water separator right before the manifold.

[damnyankee36]

I emailed Accu-Air and this was their response:

"Thanks for your inquiry! The VU4 (and all other solenoid valves on the market) will back flow when the bag pressure is approximately 15 psi higher than the tank pressure. If you would prefer that the bags would hold pressure when the tank has zero, you can install a check valve ($25 with PTC fittings) in the supply line from the tank to the VU4."

Sounds good to me! I really don't know when there would be a situation in "normal" operation where the tank pressure would ever be less than the bags.

[dznucks]

Let me know what check valve you use. I am about to install the same system and will need to do the same thing. I found some in-tank, in-line fittings that might work. this website has alot of fittings, will have to figure out which size.

http://www.drillspot.com/products/51...nk_Check_Valve

[kev2809]

you can use the ones suicidedoors has...

1/2"
[IMG]http://www.*****************/files/SMC_1-2_Check_Valve_with_Fittings.jpg[/IMG]

3/8"
[IMG]http://www.*****************/files/SMC_3-8_Check_Valve_with_Fittings.jpg[/IMG]

with no fittings..
[IMG]http://www.*****************/files/SMC_Check_Valve.jpg[/IMG]

[damnyankee36]

Originally Posted by dznucks

Let me know what check valve you use. I am about to install the same system and will need to do the same thing. I found some in-tank, in-line fittings that might work. this website has alot of fittings, will have to figure out which size.

http://www.drillspot.com/products/51...nk_Check_Valve

I didn't plan on using a check valve, but they're pretty reasonable, so I might reconsider.

[smashingchuck]

Almost all solenoid valves require some amount of back pressure. I know mine do, and I can air the truck out but simply evacuating air from the tanks.

[dznucks]

I think i am going to install one.

What happens if the compressor goes bad, will the tanks loose pressure? should there be a check valve there too, just for extra insurance?

[smashingchuck]

I don't know that it is required, but I do have one in between my tanks and compressors. Most compressors come with them.

[Hottrucks]

you can get the check vavles at any big truck parts shop...its all the same..I had to add some to my truck to protect from line blow out....

[damnyankee36]

Originally Posted by smashingchuck

Almost all solenoid valves require some amount of back pressure. I know mine do, and I can air the truck out but simply evacuating air from the tanks.

OK, here's a thought. How come the dump valve doesn't loose air? It never has back pressure, it's always vented to atmospheric pressure.

[smashingchuck]

Originally Posted by damnyankee36

OK, here's a thought. How come the dump valve doesn't loose air? It never has back pressure, it's always vented to atmospheric pressure.

if there is air in the bag, then there is back pressure.

[damnyankee36]

Originally Posted by smashingchuck

if there is air in the bag, then there is back pressure.

But not on the other side of the valve. The dump valves have bag pressure on one side and an zero pressure on the other. The lift valves have bag pressure on one side and compressor pressure on the other.

According to Accu-Air, once the bag pressure gets aprox. 15 PSI below bag pressure the lift valve will let them deflate. The dump valves always have way more than 15 PSI below bag pressure on the open side under normal conditions.

[smashingchuck]

You're only confusing yourself. Valves are directional, in one way, out the other. You never need pressure on the "out" side. Just the "in" side . Get it?

[damnyankee36]

Originally Posted by smashingchuck

You're only confusing yourself. Valves are directional, in one way, out the other. You never need pressure on the "out" side. Just the "in" side . Get it?

Nope. Let me think about this!

[AccuAirSuspension]

Originally Posted by damnyankee36

But not on the other side of the valve. The dump valves have bag pressure on one side and an zero pressure on the other. The lift valves have bag pressure on one side and compressor pressure on the other.

According to Accu-Air, once the bag pressure gets aprox. 15 PSI below bag pressure the lift valve will let them deflate. The dump valves always have way more than 15 PSI below bag pressure on the open side under normal conditions.

The intake and exhaust valves are ported exactly opposite from each other. Let me explain:

The intake valve has tank pressure on the back side of the poppet and bag pressure on the "face" of the poppet.

The exhaust valve has bag pressure on the back side of the poppet and atmosphere on the "face" of the poppet.

Anytime you have approximately 15 psi more on the "face" of the poppet than the backside, the pressure will overcome the poppet spring and the valve will back flow, (This is the case when your tank pressure drops below the bag pressure).

This is why your exhaust could never back flow. Now lets get really crazy about this... if you had zero psi in your bags and the atmosphere suddenly went 15 psi higher than your bags, then the exhaust valves would back flow and your bags would automatically start inflating!!!! I don't think that we should worry about this one though

To further the original question about adding a check valve... All of the suggestions are true... a check valve will surely eliminate the potential back flow concern when your tank pressure drops below your bags. But also keep in mind that a check valve is another part to fail. I'm sure that quite a few people could way in on how many compressor check valves they have had fail in the past. At AccuAir we have solved the whole issue by providing leak free plumbing... yes sounds crazy, but loctite 565 along with top-of-the-line D.O.T. fittings have changed our world.

[damnyankee36]

Originally Posted by AccuAirSuspension

The intake and exhaust valves are ported exactly opposite from each other. Let me explain:

The intake valve has tank pressure on the back side of the poppet and bag pressure on the "face" of the poppet.

The exhaust valve has bag pressure on the back side of the poppet and atmosphere on the "face" of the poppet.

Anytime you have approximately 15 psi more on the "face" of the poppet than the backside, the pressure will overcome the poppet spring and the valve will back flow, (This is the case when your tank pressure drops below the bag pressure).

This is why your exhaust could never back flow. Now lets get really crazy about this... if you had zero psi in your bags and the atmosphere suddenly went 15 psi higher than your bags, then the exhaust valves would back flow and your bags would automatically start inflating!!!! I don't think that we should worry about this one though

To further the original question about adding a check valve... All of the suggestions are true... a check valve will surely eliminate the potential back flow concern when your tank pressure drops below your bags. But also keep in mind that a check valve is another part to fail. I'm sure that quite a few people could way in on how many compressor check valves they have had fail in the past. At AccuAir we have solved the whole issue by providing leak free plumbing... yes sounds crazy, but loctite 565 along with top-of-the-line D.O.T. fittings have changed our world.

That helps me immensely! I didn't realize the valves were opposite in their configuration in relation to the bags.

I remember a while back I was wondering how tough a solenoid's job is if it had to have enough spring pressure to keep it sealed yet a strong enough magnetic field to open it. The air bag pressure actually helps hold it shut, at least on the exhaust valve.

Thanks!