Pressure Relief Valve for less than 15 psig 3

[knowlittle]

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.

 

[moltenmetal]

A Bunsen burner is open to atmosphere. No meaningful relief can be provided on something connected directly to the atmosphere.

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.

 

[knowlittle]

1. Thank you for the note. We are a chemistry lab and I don't have the knowledge to fully comprehend your note. But I will look into "excess flow check valve" and "spring loaded check valve".

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.

 

[LittleInch]

molten metal - with respect, maybe you forgot what a Bunsen burner looks like - there is a very small orifice involved and if the regulator on what sounds like a ridiculously sized gas bottle went wrong, then you could very easily go critical flow on the orifice and expose the upstream pipe to whatever the regulator decided to put out. Hence the "throttling valve" you refer to is in fact the burner jet.

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.

 

[GenB]

Co nbraco Ind. Makes Code and non code press. Relief valves. In the USA you can search McMaster Car, Grainger, remember if you use on fuel gas, ventinng sha be to a safe location. To atmosphere or other.

General Blr. CA,USA

 

[knowlittle]

LittleInch and GenB, Thank you for the reply. The ASTM test procedure requires methane gas. I suppose it is related to heat input (rate and total amount).

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.

 

[moltenmetal]

Let's see if I understand this: you are taking gas from a DOT cylinder and using it to feed a bunsen burner via a flex hose, but you're worried about the regulator failing open and rupturing the flex hose, right?

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-Flow

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.

 

[GenB]

I have used gas vents in the pass. I will check if the info is still available. used for back pressure on Nat gas burners 2 to 5 psi system.

General Blr. CA,USA