SpudFiles

I've read on the forums that aluminum or metal pistons are too heavy and plastics (Delrin, HDPE, UHMW) are preferable. But what if the pistons are holding in the air pressure? Such as BTB's balanced push-button valve.

I'm scaling up his design for a 2 in. toolie type balanced valve. The two equal sized pistons must be able to contain 300 to 350 PSI. Thanks!

Nothing wrong with using metal pistons as long as you form it into some sort of structure as opposed to using a solid cylinder.

Thanks Jack. The pistons will be about 2" diameter and .30 width. Below are pictures of one of the pistons. The other will be the same size.

As you can tell by the photos, I'm no photographer.

When engineering a valve of this size it becomes important to do the math as the forces involved can be quite high on the components.

300 PSI on a 2 inch valve disk is about a half ton. Be sure your parts can operate with this force and dynamic forces while operating.

Safety first.

Thanks for the concern, Tech. I'll do the math and a lot of testing at low pressures and slowly graduate to full pressure.

Aluminum works awesome if you have machining skills,, I had a toolies piston made its awesome!!!

If you make the two sides equal you're basically making a QDV.
Both sides experience the same amount of force, but in opposite direction.
It takes an external force ( pullrod) to move the piston and once the valve is open, once more side of the piston is exposed to the pressure, slamming the piston open fully.

My so-called balanced valves are actually not balanced 50/50.

They are poppetvalves with an opposing piston to cancel out most of the forces.
This results in a large poppet, wich can still be pressed or hammered open with little effort.

You couldnt knock back a half-a-ton-hammervalve with a sledgehammer,
Things change if you have a piston taking out almost half-a-ton.

a counter-balance...

Brian the brain wrote:If you make the two sides equal you're basically making a QDV.

Exactly what I had in mind. This one is balanced 50/50 or you could say 100% counter-balanced. It will open up into a 3" barrel. Not a lot of room for the air to get around but I think it will be enough.

If it would retract, away from the barrel, it would allow 100% flow and pop open really fast once the air pushes on the newly exposed front.

If you mean to push the piston out, towards/into the barrel, the disc is in the path of the airflow.

Brian the brain wrote:If it would retract, away from the barrel, it would allow 100% flow and pop open really fast once the air pushes on the newly exposed front.

I'm guessing you mean design it like Tech's QDV.

Brian the brain wrote: If you mean to push the piston out, towards/into the barrel, the disc is in the path of the airflow.

The 2" piston would be going into a 3" barrel. The barrel OD is 3 1/2" so the ID of the barrel's coupling would be 3 1/2". I'd extend the coupling so the 2" piston opens up inside of the 3 1/2 " ID coupling. 4" would be ideal but I think 3 1/2" should still work. What do you think? Should I go ahead and design it like Tech's QDV? Thanks!

What do you think? Should I go ahead and design it like Tech's QDV? Thanks

I think you should decide.

I'm just pointing out the disadvantage of push-forward opposed to pull-back.
It'll restrict flow and will therefore be less powerful.
There could be other factors involved that would make the push version apealing however.

it could be linked to a blow forward valve for instance.In case you planned a BFV anyway, you probably wouldn't notice any difference in flow or power between the two.
The BFV-link should be able to pull the piston along with it and create that pop.
In that case I'm not entirely sure on how well it will reset under pressure.
But the pull type doesn't always reset automatically either I guess.

Thanks Brian. I think I'll keep on experimenting.

Just curious, but has anybody used or milled solid bars of teflon for the construction of breaches or pistons.

Any feedback on using solid teflon as a construction source would be appreciated.

Teflon doesn't come cheap here...IIRC the last piece I bought from Johnston Plastics in Edmonton ran $32 or so for one foot of 1". I don't think you could buy it in less than one foot lengths.

I have used a teflon button set into the face of a nylon piston and retained with a screw.

Teflon would not make a suitable breech IMO.

BigDeutcher wrote:Just curious, but has anybody used or milled solid bars of teflon for the construction of breaches or pistons.

Any feedback on using solid teflon as a construction source would be appreciated.

I have a Teflon piston in my mini and it is working well so far. Not sure if I will buy it in the future for making pistons, but I had a short length of it that I got off a scrap pile some time years ago.

It might be kind of expensive for larger pistons, not sure.