Simple Bleed Valve

[rsterne]

I'm sure many of you have wanted a bleed valve so that you could make a PCP (or CO2) fill station and couldn't find a simple, inexpensive one.... I know I certainly have.... I've made a few different ones, but this one uses easy to get parts, although a lathe is certainly a big help.... Here is the exploded view....



The body is a steel male-male adapter, with 1/8" NPT on one end and in this case 1/4" NPT on the other, although that isn't critical.... All you are after is a large enough OD to be able to drill and tap it for a short 3/8"-24 NF bolt and have it strong enough to withstand the pressure.... If you look closely, you can see the 1/16" vent hole on the bottom of the larger OD section, between the threads and the hex.... All I did was drill in on the large side with a size "Q" drill (you can use 21/64") which is the size to accept the tap, far enough to create a seat for the plastic seal just where the hex starts.... and then tapped it about 1/2" deep for the bolt.... You want lots of threads so that the bolt can be unscrewed many turns before it comes out.... The plastic part can be Delrin or Teflon, even Nylon.... The pilot is a loose fit in the through hole in the small side of the adapter, and the taper is 30*, just a bit steeper than the taper on a drill point, so that the seal occurs at the smallest diameter of the seat.... The OD of the plastic piece is 5/16", a loose fit in the drilled hole.... You simply drop the plastic part into the hole, screw in the bolt until it presses it gently against the seat and fill your gun.... After you turn off the valve, you unscrew the bolt a fraction of a turn and the air in the hose vents through the small hole, allowing you to remove the hose from the gun....

It isn't very elegant, and could be made a lot prettier with a custom piece without the large threads on the outside.... but it is pretty easy to make and works perfectly.... You could probably use a 6mm airsoft BB for the plastic seal, but I never tried that....

Bob

[Bill L.]

Thanks for posting this Bob,I am going to use it for a manifold set up I'm making for my 6000psi nitro fill setup.Will it release at less than half a turn?
Thanks,Bill

[rsterne]

At 6000 psi you will have a fair amount of load on the seat.... so my only concern is friction on the threads of the bolt.... You won't know until you try it how hard it is to undo the bolt.... The way it's designed, you only have to tighten it enough to seal.... and assuming you do that (and don't crush the plastic) then you only have to undo it a fraction of a turn.... At 1500 psi mine bleeds down when backed off less than 1 flat (1/6th turn)....

If you find that you can't undo it by hand, then you need to make the seat area smaller.... Mine seals on the inner edge of the seat, where the diameter is only about 3/16", so at 1500 psi the end force is only 42 lbs.... with a 24 tpi bolt, that only takes a tiny force to turn the bolt head....

Make sure you have LOTS of threads on the bolt.... not for strength, but so that it is still engaged a good distance when you are bleeding the hose....

Bob

[vigilandy]

Bob-- I recall seeing a thread about drilling a hole in the ASA to allow venting.   I can't find the post anymore though. 

Something like this:  http://www.ebay.com/itm/281299669007

What do you think of this for HPA use?

[rsterne]

That allows venting when the ASA fitting is unscrewed from the top of the regulator.... QB tank blocks are vented in that manner.... It works fine for CO2, but the higher the pressure the more likely it is to shred the O-ring on the regulator.... Some O-rings are tougher than others, of course.... I would not use that for an every-use bleed valve, it could get expensive on O-rings....

Bob

[Bill L.]

Thanks Bob,I have a regulator on the tank and I don't fill any of my guns more than 2000psi. so it should work fine.   

[vigilandy]

Thanks for sharing from your well of knowledge Bob. 

[Bill L.]

Bob-- I recall seeing a thread about drilling a hole in the ASA to allow venting.   I can't find the post anymore though. 

Something like this:  http://www.ebay.com/itm/281299669007

What do you think of this for HPA use?

From the description..."When knob is unscrewed the remaining gas inside the adapter is released to prevent CO2 bursts and o-ring breaks when you remove your tank from the adapter".If so this would work well on a buddy tank for my guns.I think I will buy one just to see how it works.

[rsterne]

Didn't see that.... good idea if it works properly without blowing the O-ring sealing the stem.... I made one but the O-ring life was iffy, especially at high pressures....

Bob