Air Operated PVC Water Dump Valve

For an upcoming Maker Faire project, I needed a cheap, air operated valve to quickly dump a column of water. After looking at what was available commercially, the cheap portion couldn't be obtained.

So after some pondering and one prototype, I came up with this. Is uses a 3/4" adjustable PVC pipe extension as the pneumatic cylinder and a 1" PVC cross for the water inlet, outlet, and dump port.

I have about $10 in this valve and for what I need it to do, it works well at a pilot pressure of 60 psi.

Please note that I used a 12" x 36" lathe to modify some of the parts. I understand that most people won't have access to this type of equipment. I used the lathe out of ease and reliability. The parts I machined on the lathe can be modified with some sand paper and elbow grease.

Please note that all standard "do at your own risk" disclaimers apply. I am not liable for anything. You accept all responsibility. You know the standard CYA that keep me from having any culpability if you or others get hurt or damage anything. Don't do this if you are not willing to accept all responsibility for your actions.

This material list isn't all encompassing, but should get you most of the parts:

3/4" adjustable PVC pipe extension

1" PVC pipe cross

3/4" PVC pipe (about 6 inches)

3/4" PVC cap

#215 Oring (I used Buna but viton is good too.)

Purple Primer

PVC pipe cement

3/4" to 1/2" npt pipe adapter

Open up one of the Cross' ports so that the pipe extension can slide into the port. The clearance should be close so that the parts can be cemented together.

There are several modifications to the adjustable extension:

1. Disassemble the extension and remove the second oring on the inner rod (piston). Save the oring for later.
2. Remove the oring groove from the piston.
3. Turn down a piece of 3/4" pipe so that it will go into the larger opening on the piston. You will use this to create an oring groove to hold the removed oring in place. After turning down the pipe, cut it to 3/8" long. Try to keep the cut as square as possible.
4. Carefully glue the 3/4" pipe into the piston. The 3/4" pipe should not be bottomed out, but should leave enough room for the oring to fit into. Quickly wipe away any extra purple primer or cement in the cylinder.
5. After measuring the location of the 3/4, pipe. Drill through the wall, centered on the pipe with a #20 drill bit and tap #10-32 thread. This is for the air port to close the valve.

Assemble the parts in order as shown in the picture. Use purple primer and PVC cement to secure the cross to the cylinder.

Install the #215 oring on the end of the piston. (The piston should be extended through the cross.) Check that the cap will freely go into the end of the cross. If it can, then cement the 3/4" cap onto the end of the piston.

It helps to lubricate the orings as you do the assembly.

That's it. You can put whatever ports you want on the other two connections.