Crush-Type Seal for Plastic Tapered Pipe Threads?

[SPociask]

Has anyone ever heard of using a crush seal, or some sort of o-ring seal on a tapered thread connection? I've always been of the opinion that a tapered pipe thread connection, by its very nature, precludes using a crush seal.

I am having a problem with plumbing leaks (liquid at 3 psi) between PTFE pipe connections and PVDF pipe connections (and PVDF pump head). The leaks start after several days, and reappear weekly. I believe it is because of the difference in durometer, between the two materials, and I may be experiencing some creep or cold flow in the softer teflon threads after tightening. Does this sound like a reasonable assumption? We are using teflon tape also. The crush seal was suggested as a solution, but I have my doubts that the concept can be effectively applied in a tapered pipe thread situation.

Under the circumstances, using identical plastics is not an option. Nor is using flared compression fittings. So I'm wondering if anyone has ever seen a successful application of o-rings or crush seals in a plastic taper thread?

I have included a pic of the leaking system, just for the heck of it. Nearly all the connections begin to leak after some days.

 

[milena02]

Plase do a search for "PIPE SEALING CORD"

 

[Artisi]

A few close-up pictures of an actually fitting would be more appropriate.

 

[donf]

Google "Miller Truseal".

I've had some success using these with metallic piping. No experience with plastic.

regards,

donf

 

[moltenmetal]

Anaerobic pipe thread sealant is your friend when using tapered threaded joints. These sealants do not have the same corrosion resistance as either PTFE or PVDF, but you can find something compatible with most services.

Be careful when you use these on PVC, PP etc.- make sure the sealant is compatible with the piping material. Some are, some most definitely are NOT and cause embrittlement, spot welding etc. of certain plastic materials.

 

[beetech]

Why not use hemp assuming your liquid is water. I have had problems sealing bsp threads on chinese stainless pipe fittings and found hemp is the most relible solution for plumbing up a non leak system. Note that hemp may be unsuitablle if your putting tegether a "hygenic" system.