I’m looking for a couple of relief valves for a prototype I’m making and I cannot find any that are small enough. Although the design and calculations have not been finalised I can say that the valve needs to be rated at about 8bar.

The smallest I have found so far is 20mm diameter (length is not an issue). I am hoping to get one <15mm, ideally as small as 10-12mm.

Can anyone tell me where I can find the smallest relief valves?

Regards,
Mark

Did you check with the safety valve vendors directly (see for example: http://www.andersongreenwood.com)? They are just a phonecall away...

You're likely to find the smallest relief valves for the smallest flowrates. I'd venture to say that would be for liquid thermal expansion considerations in (short) pipelines. This situation occurs in liquified gas systems, such as LPG, ammonia, etc. I know I've seen such relief valves no larger than 1/2" (about 15mm) and maybe even down to 3/8" (about 10mm). Look for Rego or Gas Equipment Company as possible suppliers of such small PSV's.
Doug