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Quick question

Unread postPosted: Tue Jan 29, 2008 8:37 pm
Author: Fnord
Has anyone used a schrader valve as a check valve?

Logically, I think it should work, but I wanted to ask before I potentially ruin some fittings and jbweld.

(Edit; if it helps, I intend to use this on a homemade high pressure pump)

Unread postPosted: Tue Jan 29, 2008 8:45 pm
Author: BigGrib
ive never done it but like you said theoretically it should work

Unread postPosted: Tue Jan 29, 2008 8:58 pm
Author: Hotwired
If we're talking an air inlet check valve yes it works.

If we're talking as part of a system where you're looking for air to open the valve and pass through only one way then you might need fairly high pressure to open it.

I've got an unscrewed schrader in front of me (because I'm going to do something to it later...) and theres about a 2mm hole for air to pass through.

That 2mm hole is blocked by a tiny rubber faced poppet with a spring holding it shut, normally opened when being filled by a pin attached to it being physically forced down by the filling head.

Your call ^_^

Unread postPosted: Tue Jan 29, 2008 10:15 pm
Author: mopherman
Sure, jsr has used them in this fashion with fine results, as have I. The only thing is the tiny flow, but if its a high pressure pump it doesnt have huge volume anyway. I say go for it

Unread postPosted: Tue Jan 29, 2008 11:52 pm
Author: jackssmirkingrevenge
When I fill with my shock pump, there's an o-ring between the pump attachment and the schrader, meaning the stem of the schrader doesn't get physically pushed down by the pin on the pump attachment, but air leaks through freely - so yeah, you should be fine.

Good luck with your pump ;)

Unread postPosted: Wed Jan 30, 2008 5:27 am
Author: Hotwired
*examines own shock pump*

Hey waddya know, theres no pin in there. Guess they're only on lower pressure pressure pumps for tyres and so on.

Unread postPosted: Wed Jan 30, 2008 6:52 am
Author: mark.f
While I'm sure it will work, I have a few suggestions.

Google "Presta" valves. They operate differently from Schrader valves, (they are held closed by pressure, not a spring, so they probably have a good surface area), and most attachments I've seen for filling them don't have a pin.

Why not just use a regular check valve? I've found them for as low as five bucks. It should last longer than a Schrader or Presta valve, in any case.

Unread postPosted: Wed Jan 30, 2008 6:56 am
Author: SPG
You might want to look at a "presta" valve as well, they're the type used on high pressure racing bicycle tyres. They use purely air pressure to open (although you can push in the valve core to vent it, and I seem to remember that they actually have a bigger "port" area than a schraeder.

Unread postPosted: Wed Jan 30, 2008 7:59 am
Author: Hawkeye
So much easier to just make a custom check valve that the pump threads directly onto. All you need is a brass reducer that has a lip on the inside that will support an o-ring.
Can you guys not get threaded reducers? You can use 1/8 male-1/4 male, 1/8 male-1/4 female or 1/4 male-3/8 female. All of these have a nice lip on the inside that is perfect for housing a check valve. Then you can just put a fitting on the end of the pump that threads onto the smaller thread of the valve. No hose, zero or minimal deadspace.

Unread postPosted: Wed Jan 30, 2008 12:53 pm
Author: SpudFarm
why not be the first to make you own? when i think of it mabe i will i have for a long time been looking for a suitable check valve for a pump but never found one so i`ll mabe give it a try.

Unread postPosted: Wed Jan 30, 2008 1:23 pm
Author: Hawkeye
Actually I believe I made the first high pressure pump with a homemade check valve on here.
It is so simple that I wouldn't even call it "making".
Assembly of parts that seemed custom made for the job is more like it.
The extent of custom work involved filing out the stop in a reducer so that the pump rod could slide freely, drilling a hole in an end cap and filing a hex nut to a round shape by chucking it in a drill and spinning it against a file. Real tough stuff.