Pressure Relief Valve for less than 15 psig
Pressure Relief Valve for less than 15 psig
(OP)
We have a methane gas cylinder (about 2000 psig) connected to a bunsen burner. I need to install a pressure relief valve (PRV) downstream of pressure regulator in order to meet our pressurized gas safety requirements. Bunsen burner operates at <5 psig.
Question 1: Do they make ASME rated PRV at 5 psig? If you know a source, please let me know.
Question 2: If PRV's are not ASME rated for <15 psig, is there an alternate code/standard that applies to low pressure PRV's?
Any advice will be much appreciated.
Thank you.
Question 1: Do they make ASME rated PRV at 5 psig? If you know a source, please let me know.
Question 2: If PRV's are not ASME rated for <15 psig, is there an alternate code/standard that applies to low pressure PRV's?
Any advice will be much appreciated.
Thank you.





RE: Pressure Relief Valve for less than 15 psig
If there is a throttling valve between the discharge of the pressure regulator and the bunsen burner, then you might need to protect the line connecting the two with a relief device sized to protect the line against excessive pressure should the regulator fail in the fully open position. However, the more practical approach is probably just to design that line to be resistant to full cylinder pressure by using tubing and compression fittings instead of hose etc.
If there is no valve, there is no practical means to protect the line by relief, nor really any need to do so. You'd be better served in that case with an excess flow check valve in the line rather than a relief valve.
ASME-rated relief valves are not required for the protection of piping- only of pressure vessels. That rule may vary by jurisdiction but that certainly is the case here. We use other devices such as non-ASME proportional relief valves or spring-loaded check valves (i.e. Circle Seal, Swagelok, Ham-Let, Parker etc.) for the protection of piping/tubing on a routine basis. As long as they're sized correctly, they are fit for purpose.
RE: Pressure Relief Valve for less than 15 psig
2. There is no throttling valve between pressure regulator and bunsen burner.
3. The instrument is a flammability tester and flexible hose cannot be avoided. The setup has a bunsen burner below test article. Once the test article catches flame, the burner needs to be moved out per test procedure. Another practical aspect is if the burner is left in place (with no gas flow), burning molten plastic may drop on the burner and clog up gas flow path.
RE: Pressure Relief Valve for less than 15 psig
I fully agree with the rest of your post and any relief valve sized for the <15psig should be good for the duty. The key will be matching the relief flow rate to the regulator max flow. And of course you need to pipe the relief gas flow away to a safe area / vent.
Can't you use a propane or butane burner instead??
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Pressure Relief Valve for less than 15 psig
General Blr. CA,USA
RE: Pressure Relief Valve for less than 15 psig
All replies above seem to indicate that there is no ASME stamped pressure relief valve for <15 psig. It will be easier to convince out safety folks (they are not code engineers) with ASME coded relief valve. Oh, well. I will investigate Conbraco line.
My gas flow is about 1-2 liters per minute. Regulator is set to 1-2 psi only. I am not sure if I can find an excess flow check valve for that low flow rate. I could not find one from previous internet search. I will do more digging later.
The test is conducted inside a vented hood. Gas cylinder sits within a foot from the hood. Plumbing vented gas to the hood will be simple.
Thank you, all. If you have additional tips, please let me know.
RE: Pressure Relief Valve for less than 15 psig
If this were my installation, I'd have two regulators in series, or a 2 stage regulator. Most people would no longer require a relief valve on the discharge solely as a protection against regulator failure. You're just dropping the pressure too much to do it in a single stage- assuming the gas in question is methane rather than propane.
If it's propane, you'll note that gas using appliances have a regulator mounted right at the tank, which is connected to the gas appliance's shut-off valves via a rubber hose. There is no relief valve to protect the hose in the case of regulator failure.
If the flow expected out of a regulator which has failed open is too small to trip a Swagelok excess flow check valve, then the need for the relief valve to me is very questionable. It is doubtful that the jet of your bunsen burner would develop enough back-pressure to cause any reasonable hose to rupture.
http://www.swagelok.com/en/product/Valves/Excess-F...
Trying to protect a piece of rubber surgical tubing or a piece of Tygon PVC lab tubing from rupture, or more likely from slipping off the end of a hose barb fitting, using a relief valve, is a bit of a mug's game, especially when the other end of the line is open to atmosphere via a jet nozzle in a bunsen burner.
RE: Pressure Relief Valve for less than 15 psig
General Blr. CA,USA