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Drop-In Check Valve

Designed with 1/2" PVC in mind.
homemade airgun parts

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#1 Buffdaddy

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Posted 25 November 2013 - 03:46 PM

As part of my continuing efforts to make a marketable DIY blaster kit, I've been working on several air blaster parts in order to find cheap methods of valve and pump construction. DIY implies that construction should be easy to understand, if not do. To that end, I'm posting instructions for replicating several important parts.

For any air gun, check valves are almost always a must. You need them to control airflow, and you need a safety mechanism (not always a valve) to regulate the maximum air pressure. If you're using actual air tubing, then miniature valves are readily available. If you're doing a PVC monstrosity, PVC check valves and such can easily run $5 or more while adding bulk and (potentially) dead space to the design.

This valve allows you to put a valve within 1/2" Sch. 40 PVC pipe, greatly simplifying any design. Cost runs from $1-2, depending on where you get your parts, and how many.

1124131955.jpg

Parts:
Two(2) 3/16" washer-cap push nuts (of this design, which is about 7/16" in OD)
cc99c138-4ba4-4f25-ab48-c0268d938fab_100

One(1) Nylon spacer, any available length, 1/4" ID by 5/8" OD
917e5b09-c582-4116-b391-5004e686fd65_100

One(1) Short length of 3/16" metal rod or tubing (I've used both aluminum tubing and stainless steel rod, depending on what was in stock)

One(1) short, weak spring with 1/4" < OD < 3/8" (often found in hardware store "assorted" spring bags or cases)

One(1) Faucet washer, trade size 1/4" or 1/4"L (9/16" or 19/32" OD)

Construction:

  • Take one push nut and press onto the end of your rod or tube. If using a tube, place a dab of Goop inside the nut to make a 100% seal upon curing.
  • Slide in this order onto the rod/tube: faucet washer, nylon spacer, weak spring.
  • Cap the other end as done above.

1124131957.jpg

The nylon/rubber interface provides the seal. 3/16" tubing or rod is used so that air can move around the shaft, and to keep the rubber washer in place (snug, airtight fit without adhesive). Finally, this particular push nut is used because its diameter allows it to move within 1/2" CPVC, which has an ID slightly less than 1/2".

To prepare your 1/2" PVC, cut a piece of 1/2" CPVC to the same length, minus the length of your spacer (error on the side of too much CPVC). Bevel the end of your PVC with a plumbing tool or knife, then hammer the CPVC inside the PVC. After letting the plastic sit for a day or so (allowing the PVC to conform to the CPVC inside to expand the ID), grab a spare piece of CPVC and use it as a spike to hammer the first piece the rest of the way into the PVC. Then use elbow grease to pull your impromptu spike out. The PVC should now have a wide enough ID to simply push the check valve inside (spring end first) and secure with super glue.

Drawing of installed check valve:
checkvalve.png


Edited by Aeromech, 23 November 2015 - 08:10 AM.

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#2 Exo

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Posted 25 November 2013 - 05:49 PM

So, uh, not sure if this was in there and I'm blind, but what was your cost to make one of these?
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#3 Buffdaddy

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Posted 25 November 2013 - 05:50 PM

So, uh, not sure if this was in there and I'm blind, but what was your cost to make one of these?


Edited; I knew I left something out!
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#4 Draconis

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Posted 25 November 2013 - 07:19 PM

To prepare your 1/2" PVC, cut a piece of 1/2" CPVC to the same length, minus the length of your spacer (error on the side of too much CPVC). Bevel the end of your PVC with a plumbing tool or knife, then hammer the CPVC inside the PVC. After letting the plastic sit for a day or so (allowing the PVC to conform to the CPVC inside to expand the ID), grab a spare piece of CPVC and use it as a spike to hammer the first piece the rest of the way into the PVC. Then use elbow grease to pull your impromptu spike out. The PVC should now have a wide enough ID to simply push the check valve inside (spring end first) and secure with super glue.



Alternatively, the CPVC could have 3/8" NPT thread cut in the outside and the PVC could be tapped with 3/8" NPT threads on the inside. This would allow the whole thing to be removable and repairable later.
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