STV ver. 2 clear inline piston valve

clide · Posted: 12/27/2008 1:01 AM Post subject:

Some of you who have been around a while may remember my Straight Through Valve that I posted on Spudtech. It was an attempt to make a piston valve with a strait flow path to hopefully improve efficiency, but while it did work there weren't really any gains in performance and it wasn't very easy to construct. Initially I planned on creating version 2 from scratch in a wye, but when researching pressure rated wyes I found a lot of wye strainers. It occurred to me that these would fit my needs perfectly. They are available in a wide range of sizes and pressure ratings, and they have a seat and and pilot plug built in. This plug even has a smaller threaded hole in the center in most cases for easily attaching an exhaust valve.

The best part about this discovery was that there were several clear PVC strainers up for auction on ebay for a reasonable price (compared to clear fittings of that size). So I decided to get one and throw together this valve and fixed up a golfball barrel and an old chamber to compliment it. Writing this post reminded me that I wanted a clear blowgun for this valve and I finally found someone selling them in the US. I'll try and get some new pics once I get the clear blowgun.

Here is a video showing a few shots being fired.

Link

As you can see from the pictures the exhaust setup is pretty unique. There is a small chamber sealing piston valve built into the valve's plug. The reason for this is that the valve's dimensions as far as seat and piston diameters are a little less than ideal and will bounce the piston with a small exhaust valve such as a blowgun. I didn't want to add a large exhaust valve to the outside. A good solution to this would normally be a DFTV type setup, but since this valve is clear it offers a unique opportunity to help explain piston valve and I didn't want to add something that would be confusing (the chamber sealing exhaust valve is hidden enough that it can be ignored completely for explanations). I must give props to GGDT here because it predicted the valve bounce and predicted that the exhaust valve planned was large enough to stop the bounce.

The piston itself is pretty standard for my guns. Lathed down from miscellaneous PVC fittings with an o-ring and a homemade check valve that doesn't seal perfectly (for safety). The fill setup snakes around a bit, but it gets the job done, keeps it low profile, and positions everything nicely.

The unions are 2" female threads so they adapt perfectly to the chambers and barrels I use with my 2" tee valves. When I first got the strainer I was a little discouraged because I thought it had a big crack running through it, but luckily the guy who sold it to me was smart and told me about knit lines. I was surprised that I had never noticed them before on normal fittings. If you look very carefully on fittings like tees on the opposite side as the mold injection point you can see faint lines that look like hairline cracks.

This gun was actually completed in October of 2007, but I was trying to hold off posting my guns as a motivator to get some stuff done. After over a year and not much progress I think I may need to take a different tactic. I'll be trying to get my stuff posted before going back to school since I'll probably be busy looking for a job next semester.

I haven't done any extensive testing, but initial tests indicate that it's probably not a huge performance boost over a similarly sized tee valve, but it is easy to build and gives a lot better performance than other inline valve options.

I usually don't give out many hints on my future projects, but I do have some 1.25" stainless steel strainers rated at something like 1500 psi. Hopefully I can do something cool with those once I get some money/time. If anybody is interested in one I do have more than I need. I would be willing to sell a few for $25 + shipping, send PM if interested.

Gee, I wonder what would be a nice accessory for a clear valve...