spot free pvc end caps cracking

[celica]

Has anyone else had trouble with the pvc end caps on their membrane tubes cracking. It a Ginsan r.o machine. It's a fine hairline crack that usually goes between the inlet and outlet fittings. Is this a result of the cycling of 170 psi on and off, which causes a eventual stress crack. This is the 3rd one in 10 years. It seems to me that plastic is a pretty poor choice of material for this application. If the R.O housing is made out of S.S, then the end caps should also be metal.
Has anybody else had this problem and what did you do.

 

[MEP001]

I've never seen a metal housing with metal caps. I've also never seen a problem with them cracking. There might be something happening which causes the pressure to exceed 200 PSI.

 

[washnvac]

In my experience, when anything plastic cracks with a female threaded receptacle, the male fitting has been screwed in too far. When I have to thread into a membrane cap, I use lots of Teflon paste, and only tighten about 1/2-3/4 turn past finger tight. If it leaks, I turn gently until it stops.

 

[MEP001]

In my experience, when anything plastic cracks with a female threaded receptacle, the male fitting has been screwed in too far. When I have to thread into a membrane cap, I use lots of Teflon paste, and only tighten about 1/2-3/4 turn past finger tight. If it leaks, I turn gently until it stops.

That's a definite possibility. Where are the caps cracking, around the fitting threads or elsewhere?

 

[mac]

This is fairly common and is caused by what washnvac said. Use his method to install for best results.