PTFE or fibre washer on a cylinder?

[stardanny]

Hi.

I was talking with my mate during a fit out of a new heating, talking about the connecter to hot water cylinder, he said to me, we should use a fibre washer for 1 inch male thread connecter to top of cylinder, I said we should use PTFE tape and jointing compound. He said fibre washer work on imm. heater so why not on connecter? To all, what you think? PTFE or fibre washer? and why?

 

[hi-spec plumbing heating]

ptfe, jointing compound.

 

[nickso]

ptfe or jointing compound

 

[mrgas]

ptfe

 

[JohnD]

if you use PTFE, what does the jointing compound stick to?

 

[gasmick2]

P T F E tape i can understand you thinking this way but when you look at an imm heater there are 2 flat sevices thats why its ok to fix a fibre washer with it be carefull what sort of sealing compound yu use as p t f e is oil based and some compounds are oil based as well by the way someone onece ask me what does p t f e stand for i thought for a moment and said "plastic tape for ease"

 

[JohnD]

Plumbers
Tape
For
Everything

 

[chrishutt]

I thought it was Plumbers' Tape For Everything.

Actually the point about washers versus thread sealant is to do with whether the threads are parallel or tapered.

Two parallel threads (as on immersion heaters and their bosses) will never lock together and so they act like compression threads, just forcing two mating surfaces together. The mating surfaces in this case are "flats" so a flat washer is an appropriate seal. Compression and union joints use parallel threads, so the threads themselves do not provide the seal.

When one of the threads is tapered (always the male one) the threads will get tighter as they wind together (no sexual innuendo intended!) and eventually lock tight, so thread sealant will do the job. Female threads are always parallel but if you had two tapered threads (male and female) they would lock up rather abruptly and wouldn't form such a tight joint.

 

[stardanny]

Excellent. Have to print this off, that tell him off. He own me a pint.

 

[bengasman]

ptfe string is the dog's for tapered threads

 

[Stivino]

It's polytetrafluoroethylene.

 

[bengasman]

It's polytetrafluoroethylene.

minus last o; also known as teflon

 

[jas05]

Different uses for jointing compounds, tapes etc.

http://www.bssuk.co.uk/bsscomm/assets/gfx/links/BSS-BOSSConsumablesRangeGuide.pdf

 

[croydoncorgi]

When one of the threads is tapered (always the male one) the threads will get tighter as they wind together (no sexual innuendo intended!) and eventually lock tight

OP was referring to a DHW cylinder. Most / all come with male and female bosses, in a standard (BS?) arrangement with male bosses for the coil connections and female for the DHW outlet. However, manufacturers (eg. Albion) will supply whatever bosses you want - male or female, in any location.

I think you will find that SPECIFICALLY in the case of copper cylinders, most / all suppliers outlaw the use of ANY taper-thread fittings (because the bosses are only fixed to the thin copper tank-wall and would get torn out by the torque required to tighten a taper-thread fitting).

 

[chrishutt]

I think you will find that SPECIFICALLY in the case of copper cylinders, most / all suppliers outlaw the use of ANY taper-thread fittings (because the bosses are only fixed to the thin copper tank-wall and would get torn out by the torque required to tighten a taper-thread fitting).

Yes, normally all the threads on the cylinder will be parallel because the male threads (usually just the coil connections) are intended to be used with union connections where the seal is made between the male cone on the union fitting and the inside rim of the end of the male thread.

However the compression fittings that screw into the female tappings will have taper threads on their male threads. These joints require tightening with some force and I've never heard of a cylinder failing as a consequence. Of course if the fitting has an adequate flange at the end of the male thread then a washer could be used to seal the joint as an alternative to thread sealant provided the male thread wasn't too tapered and allowed the flange to compress the washer on the flat of the cylinder.