Self-closing piston valve (brass fittings)

MRR · Posted: 03/09/2009 9:54 AM Post subject:

This is the way I build a high pressure self-closing piston valve (barrel sealer).

min. actuation pressure: 30 psi (varies due to the used spring and piston)

The parts:
1/2" quick connect (only to connect a blowgun, not to pressurize)
3/4" female to 1/2" male
1" female to 3/4" male
1" nipple (find one with a smooth surface inside)
1" tee
3/4" hose barb
1" to 3/4" reducer
1 bolt 2 fitting nuts
3 sealing gaskets (3/4")
1 washer -> size of the sealing gasket
2 washers -> I.D. of the 1" nipple

Step 1:
Screw the 3/4" hose barb into the 1" to 3/4" reducer and then the reducer into the 1" tee.
Nice about these hose barbs is that they have short threads, so there is enough space to add multiple barrels.

For this valve I chose a large tee compared to the "barrel" to have a good air flow and a smaller pilot chamber.

Step 2: build a piston (optional way)
This is basically a bolt piston but with two tricks I want to show you.

If you have ever build a bolt piston you might have realized that it is not that easy to get the washers into one line. Simply take two nuts and grind one side of them to form a cone. This way your washers are always centered (you can see it on the right nut on the picture).

To make the piston seal, take two sealing gaskets that are little smaller than your housing (in this case 1" nipple -> 3/4" gasket). Place them between two washers and nuts. Now screw the nuts so that the gaskets squeeze out. This way you get a perfect sealing piston.

Step 3: Assembling of the pilot section
Quick connector -> 1/2"male to 3/4"female -> 3/4"male to 1" female

Optional: Quick connector -> 1/2"male to 1" female (if you find one, even better)

Step 4: Finding the right spring (this step needs some tweaking)
You have to find a spring that is not to strong or to weak.

to strong: The piston only opens at very high pressure with bad flow or it doesn't open at all.
to weak: The piston doesn't seal and the air leaks out of the barrel.

If you think that you have the perfect spring but the air still leaks out of the barrel then your piston might seal to well in it's housing. A little equalization should be installed.

Picture of the pilot chamber. It's already small but still improvable. The valve can be actuated with a blowgun @ 30 psi.