PRD Vent Pipe Installation
(Click any pic for a enlarged view)

There are a bunch of rules in NFPA 52 that deal with every aspect of venting the PRD (Pressure Relief Device). I am not going to quote all of them, however I will refer to some that apply to this post. NFPA 52 section 6.4.1 to 6.4.8 deal with PRD venting.

"An easy way to comply with NFPA 52 is to design your systems to avoid the rules."

This is a flange off a Cavalier tank cradle. It was left over when I sawed the a bunch of cradles apart. It is where the Cavalier's PRD vented through the floor. The rubber isolation grommet will be a perfect fit for my PRD vent tube to pass through.

Here the isolation grommet is installed into the drilled hole. It provides a perfectly tight fit for the 3/8" tube I will be using.

For extra protection I have wrapped yellow teflon tape on the PRD threads. Yellow teflon tape is thicker than white and red teflon tape is thicker than yellow. The bigger the threads, the thicker the tape needed.

This is a propane adapter fitting. It has a 45° inside flare that matches the PRD's outside flare. I just could not justify a 316 stainless fitting here.

Here the offset is measured to get the vent pipe centered on flat metal.

This is a CNG fill pipe assembly salvaged from a Cavalier. It will supply all the tube needed for both vent pipes.

Here is a view of the right hand vent pipe. I used a brass flare nut for fit up purposes while I wait for a pair of steel ones to arrive from Discount Hydraulics.

This is a view of the left hand vent tube fit up. Neither the right or left vent tube could center on flat metal.

NFPA 52 (6.4.5) requires that the PRD pipe be protected against bugs and debris from lodging in the pipe. I decided to use a cap off a CNG flare fitting.

NFPA 52 (6.4.6) requires that whatever you use does not restrict gas flow. This cap is a very snug fit, however would never restrict a 3600 psi discharge.

Venting the PRD was pretty easy and did not require any trick brackets or funky clamping. The only bought parts were the steel flare nuts which were .85 cents each everything else was salvaged or in my stock fitting drawer.