SpudFiles

Since the main difficulty right now with the building of QDVs is the ability to construct a housing that's usable at very high pressures, I'm proposing a solution, which I hope I can make use of. While it's not genius, I don't think I've seen it proposed anywhere before.

Taking a threaded cross or tee, thread in four nipples, all of which are smooth on the inside. Prepare a "spacer," something with the same OD as the ID of the two nipples the piston will slide through, and long enough that when placed inside of the cross or tee, it protrudes from both ends significantly. Polish and lubricate the spacer. Fill the cross or tee with epoxy YAY!, then slide out the spacer and drill out the ports perpendicular to the spacer through the nipples, which are probably permanently attached now.

Thoughts?

It's a good way of keeping o-rings from being chewed up on the edges of the nipples, but what's to stop you from just using a tee in the same way?

To really take advantage of the extra flow in a QDV, I think Tech has said you'd need to use a cross design, but I guess there'd still be some improvement with a tee. The idea is that this construction method would produce a design that is internally almost identical to Tech's QDV constructions.

Male tees are rare and very expensive, especially for larger sizes. Male crosses don't exist, to my knowledge. I hope that answers the question... It was a little unclear.

I've considered using a 4 inch T, a pair of 4 inch to 2 inch reducers, and a 2 inch pipe in the traditional coaxial QDV design. The reducers would have the threads filed out till the 2 inch pipe fit, then welded together. It should be good for high pressure.

It would be a 2 inch QDV coaxial in a 4 inch T.

It's the welding/brazing issue that's even a more serious problem than price, in my opinion. Most members of spudfiles cannot braze or weld (I certainly can't), but all of us can purchase and mix epoxy... I hope.

I see no reason that design wouldn't work, but the ability of most to build it is questionable.

It should work with epoxy. With balanced force on the insert, the epoxy is mostly needed just for a seal.

I think I get it but would you mind making a sketch. If its what im imagining, it would work I think. The piston could easily be made from washers and a bolt to I think.

What do you mean by the "insert?" If you're referring to the epoxy, it should be "epoxied" onto all surfaces inside the cross/tee and be completely stationary... that's assuming I find some way to roughen the inside of such a fitting.

if your using galvanized fittings the insides are rough enough already but you can use a broken drill bit to add a bit.

Take a 4 inch T. Screw in a couple 4 inch to 2 inch reducers in both ends. Now a somewhat long pipe nipple can't fit all the way through the T, it can only screw into one end.

File out the holes in the reducers until the pipe nipple can fit through the reducers.

Cut slots into the 2 inch pipe the same way they are done in a coaxial QDV and glue it in place so the threaded ends of the nipple stick out both ends of the T. The cap and knob goes on one end and the barrel screws on the other. The middle of the T screws onto a chamber if you haven't figured that one out.

Technician1002 wrote:glue

Yeah... Don't really like that part. I was fully aware of the rest of the construction process, and even that you've suggested fitting a nipple into a tee by removing the female threads in the tee and brazing/welding/gluing now? them together. My biggest qualm about gluing a QDV together is not only that the impact of the piston may separate the two pieces depending on where one is holding, but simply the use of glue itself (or maybe epoxy?) to hold a hybrid or high-pressure pneumatic together.

I understand where you're coming from Tech, I really do. I just think that my method merits consideration as much as yours does. I guess the biggest reason I posted this is for people to voice concerns about the integrity or effectiveness of this before I try it and risk sacrificing $37 of pipe fittings and a significant amount of epoxy.

Crna Legija wrote:if your using galvanized fittings the insides are rough enough already

I probably won't be, because I've had issues with the threads undergoing some interesting corrosion reactions to permanently attach themselves together in the damp air of my basement. Do you have any other suggestions on roughing up the inside? Would a wire wheel (or whatever they're called) work?

Does greasing a fitting prevent epoxy from adhering?

Wire wheel should work or just using a drill bit and scrape it along the edge as its spinning/

Well since it's not actually holding significant pressure, and it's supported by the cross; roughening the inside won't matter that much

That's probably true. I think the most dangerous flaw is an air bubble in the epoxy, on combustion that could cause a localized collapse and serious failure .

As soon as I get my hands on a little more moolah and some epoxy, I'm going to try this out.

i used spray on cooking oil to stop epoxy sticking, worked great don't see why grease wouldn't.