Pneumatic burst valve - what's it's real name?

Gallery, Projects and General > How do I??

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daz:
Youre right David, the pressure test is 1.6 time the max working pressure, the safety valve should be around 10-15% hugher than the normal worming pressure.
What you could also do to alay any fears or explsion is to fit a very simple pressure switch to the tank, you can buy them pre-set and adjustable. That way the pressure switch will interrupt the compressor at the correct pressure, if that fails then the safety valve will pop. I have NEVER seen a pressure switch fail in the open position so all should be well. I have been working as a refrigeration engineer for quite a few years before the job I am in now and also used to repair compressors. The set-up I just mentioned were used all the time on both systems and always passed the insurance examination. Oh, and some of the system I have worked on run at silly pressures, sometimes 30 or 40 times what you are proposing.
If you need any more info regarding pressure switches etc feel free to contact me.

cheers
daz

loply:

--- Quote from: David Jupp on November 16, 2011, 10:10:40 AM ---If the box is totally filled with liquid, then the hazard due to stored energy is not great - if there is a head space of compressed air (say if air is used to drive the liquid out) then there is much more stored energy involved (to drive parts of the box towards you at high speed if things go wrong).

You should also consider mal operation (e.g. could it be pressurised without any liquid inside?).

I don't mean to be unduly alarmist...

--- End quote ---

This is precisely what I'm wary of. The box will have a regulator where the air enters it, but clearly it could be accidentally tampered with or could fail in some way or through some other mistake the thing could end up at 100psi with or without liquid in it. Shouldn't happen, but you never know!

I thought a burst valve nipple type thing permanently threaded into the box somewhere would be the best do-it-and-forget solution. The regulator could be removed or fail etc, whereas the burst valve would be more or less foolproof.

I just want a solution which I needn't ever worry or think about. Will keep trying to track down somewhere to buy em!

Lew_Merrick_PE:
You are basically making a "burst plug" for you system. I use them with fair regularity in gas generators to insure that the gas inside the chamber has reached a specific pressure before being passed along to the rest of the system. In this application, they are called "burst shim." The real question is, what exhaust flow rate would you need for safety? That establishes the size of the hole (orifice) you need.

I normally pay to determine exactly what the ultimate tensile and shear strengths are of any material being used for this type of application -- and then only use part of the sheet I had tested for my burst shims. Book values for these ratings will either by typical or minimum -- and there is a world of difference and variation between a book value and what you actually get! Book values will often leave you ±15% or more from your desired end.

Given your pressure and the fact that your ullage for the system is compressed air, it would be a lot simpler to get an off-the-shelf pressure relief valve and calibrate it with a ±1% pressure gauge. Just be sure to evaluate the Cv of the relief valve against your total required flow for the worst case scenario. Also, remember that the SCFM listed at whatever the rated pressure is represents the volume of air at atmospheric pressure and not the operating pressure (and remember that the values for figuring this should be represented in PSIA -- PSI-Absolute -- rather than PSIG -- rather than PSI Gauge)!

naffsharpe (Nathan):
Hi, We used to use a burst disc fitting on pressure wash pumps and also on small pressure accumulators. For most pressure washers the pressure would be way above your requirements but I do recall that they were available in quite low burst pressures. We used to source ours through Hayley Bearings ( UK ) trading as Bearing Man. This was however some time ago. The fitting itself was just a Wade type bsp/cone compression fitting with the burst disc replacing the compression "olive", disc material was normally plastic of some kind with heavy score marks to allow it to rupture. You could easily make your own and test it on your air line.

Nathan.

Pete.:
The reason pressure washers use bursting discs is because they are positive-displacement pumps and the disc is there to protect the pump hardware should there be a blockage in the gun. A relief valve is better for a compressed-air system.

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