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Manufacturer's valve max. PSI rating vs. actual

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Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: air_dannon » Tue Dec 03, 2013 12:19 pm

Hi,

I've been looking around (again) for a commercial QEV that can handle 400 psi (my attempts to make one have failed too often). This one (I believe) was used by member, mpmrla for his rifle on this post. The manufacturer's max pressure is under 200 psi, but mpmrla is taking it to almost double that. I understand companies give themselves a safe margin when stating pressures, but it seems like most pneumatic veterans here go well beyond that and I'm wondering if there is a consensus on what is acceptable overclocking with valves ;) I'd hate to get the Alpha, take it to 400psi and have it leak or fail.

Thanks!
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: Brian the brain » Tue Dec 03, 2013 3:51 pm

It depends on the type of valve, brand, etc.

The only way to be safe is to hydro-test it.

Fill it up with a liquid and pressurise it beyond what you intend to use.
Keep a safety marging of , I'd say. 1/3
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: jackssmirkingrevenge » Tue Dec 03, 2013 10:11 pm

Also be aware that failure may occur in the form of piston rupture, which would result in inadvertent firing. In general catastrophic failure is unlikely to occur, as opposed to premature wear. Just make sure you're constantly aware of the risks you're taking and the potential consequences.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: bravootome » Thu Dec 05, 2013 3:15 am

air_dannon wrote:Hi,

I've been looking around (again) for a commercial QEV that can handle 400 psi (my attempts to make one have failed too o



i had shown my qev to a friend of mine, he made a qev that uses over 400 psi, it all about the material the piston is made of and the way it reduces shocs(?) i am not able to tell you the name of material cause google cant translate it. But if youre interested i may take a photo of the material and show it to you.
i,ve pushed my qev to 35 bar bar and it works well, but it is too much for bb's, and too much weight on the pilot. But it works.
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Last edited by jrrdw on Thu Dec 05, 2013 5:59 am, edited 1 time in total.
Reason: Fixed quote tag.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: Ragnarok » Thu Dec 05, 2013 7:07 am

bravootome, that's what I'd think of as a "European" use of the term QEV.

The way the history of these things turned out in the English speaking community meant that the home-made equivalents had common names years before the commercial versions really started to get used - so the term "QEV" only really ended up referring to the commercial valves, at least in English use.

To me and many others, even though these valves operate on the same principles:
Image
(For the sake of clarity, the ball valve to the right is "just" a safety. Completely blocking the barrel off from the main valve is safer than any approach that disables the trigger).

... so you do need to watch the context when people are talking about QEVs. In this case though, the original question did specify only commercial valves.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: bravootome » Thu Dec 05, 2013 9:12 am

... so you do need to watch the context when people are talking about QEVs. In this case though, the original question did specify only commercial valves.[/quote]

it is about a purpose. the one to get a qev( reather it is comercial or homemade- It is the same thing- just the second doesnt cost -cause you dont buy it) that will work as he wants.
A comercial thing is after all at his origins a homemade one. If i made myself a airsoft rifle it is still rifle even if i didnt brought it.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: Ragnarok » Thu Dec 05, 2013 10:49 am

Your valve isn't an exhaust valve though (although the QEV in the picture above is). It's being used to do work downstream, so the gas flowing through it isn't actually yet "exhausted".

Engineering regularly gives things that work exactly the same way different names depending on what job they're doing. Injectors/ejectors are a relevant example - both work on exactly the same principles, but which is the appropriate name is depends on whether it's feeding or exhausting material.

There's an argument for calling a commercial valve by the name it was sold under, even if it's actually being used for something different (we do it all the time with sprinkler valves - where it's quite useful information, given the foibles of a sprinkler valve are a specific subset of those of diaphragm valves), but it makes less sense to just attach those names onto a home-made valve.

~~~~~

And regardless of definitions, for a lot of people the convenience of a commercial valve is considerably more important than the cost (and, in any case, most sizes of commercial QEVs are not all that expensive), so the question is valid enough.
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Re: Manufacturer's valve max. PSI rating vs. actual

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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: Ragnarok » Thu Dec 05, 2013 9:25 pm

In retrospect, I realise the above post probably comes across as really damn argumentative - with that in mind, I apologise. I'm very good at being an unintentional [female doggy], and putting you down was not the intention.

I do stand by the general points, although not the way I made them.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: jackssmirkingrevenge » Fri Dec 06, 2013 9:00 am

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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: Ragnarok » Fri Dec 06, 2013 10:30 am

Entirely true...

... but agreement or disagreement with the use of the terms, they are used in different ways by different people, so it can't just be said the context is unimportant.
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Re: Manufacturer's valve max. PSI rating vs. actual

Unread postAuthor: advancedspuds » Fri Dec 06, 2013 11:04 pm

Usually, with a metal valve at least, it's the diaphragm that is rated. I have taken a 3" valve rated for something like 12psi and made a thicker diaphragm to hold 150psi or so. So you may look into making your own from sheet rubber, or just try it, remember like was said before if it fails, it will shoot whatever projectile is in it.
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