Inflation Systems| CIRCOR Aerospace
Theseare on my Wing Tubes on my Willard and they are the same one on my friends Hurricane 733. I believe that mine are PRV-7's.
~1/3 down the page:
"The SEI Pressure Relief Valve (PRV) is manufactured with durable, lightweight plastic. The SEI PRV utilizes a unique design that will perform when needed most. The SEI PRV comes in open and close pressure ranges from .02 PSIG to 10 PSIG and several thread or installation options. Shown are the standard PRV-(X), the high-flow PRV-(X)H, PRV-(X)L, and our PRV-HFF which boasts flows to 70 Cubic Feet per minute."