How to fit a new seacock

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cpedw

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A ball valve has lost its ball so I plan to replace it. The skin fitting looks to be in good condition and I have the new valve. What should I use to seal the ball valve to skin fitting and ball valve to hose tail joints? Is PTFE tape good for this job?

It looks like there was some hemp and plaster mixture in the original (Westerly, 1986).
Thanks,
Derek
 
I have one of these valves on board for the engine cooling inlet and it's sealed with PTFE tape and hasn't given any trouble in the last 4 years so based on that I would think ok. If using hemp and paste I would make sure it was a non hardening paste to prevent cracking.
 
Hemp & Boss White used to be the standard way but is now generally only used for threaded unions in gas pipes. It is a sod to apply as the hemp tends to squeeze out as you screw up the joint. If you really want to use it, roughen the male thread by scratching a hacksaw blade across it to give a bit of roughness for the hemp to grip on. Another brand name for the goo is Plumber's Mait.

PTFE tape will do the job fine. put about 5 turns of tape on in a clockwise direction when viewing the male thread from the open end. A new lot of tape is needed every time you re-make the joint.
 
Yes I would use ptfe tape. Wind it on as Snowleopard says in the same direction that the valve is going to screw on but don't put too much on. My only reservation is that being a good nonstick lubrcant it will be easy to unscew the joints again. This may be an advantage or a disadvantage.

Are you sure this is not a sensible time to renew the skinfitting and hose tail. Look very critically at them at any rate.
 
Snowleopard nearly got it right:
Hemp & boss white was used for screwed threads although boss white is now no longer, as it is banned for use on potable water systems because of the toxic effect.
Plumbers mait was never intended to be used on threaded fittings it was a sealent for WC & lav.bsn. wastes.

Yes you can use PTFE but make sure its from a reputable plumbers merchant & not the cheap crap from B&Q. You can also get thread string, I think made by loctight which will also give you a good joint. The joint from the skin fitting to the ball valve is going to be one of the strongest in the system so don't worry about it too much.

Make sure you use bronze or abs ball valves, not brass or steel.

Personally I would also change the skin fitting as well, as the sealent has almost definitely had it. Clean the surface thoroughly & use a sika or 3M sealent.

ps. don't over-tighten it. /forums/images/graemlins/wink.gif

poter.
 
I use silicone sealant one approved for use in the marine industry under water. Also use a back nut
Simlpe, effective and easy enough to remove at a later date
just spread it around the male thread after you put on the back nut wind the ball valve on do up the back nut clean up and excess with white spirit job done!!!
Avoid sika flex like the plauge!!
 
Silicon sealants tend to do just that, ie 'seal', whereas Sika, being a polyureathane (?) seals superbly but also bonds, meaning interesting vocab if you ever need to get it apart in the future.

Having renewed all the skin fittings, valves etc on our boat, I reckoned Sika was fine for the skin fittings etc as I don't intend to take them out for many years to come.
 
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