Sealing seacock to skin fitting

Plum

Plum

Well-Known Member
Joined
6 Jun 2001
Messages
5,038
Location
UK East Coast
Visit site
If you use something like Sikaflex 292, as used on the through-hull skin fitting, to seal the threads when screwing the ballvalve on, when it comes to replacing the ballvalve it is usually a hacksaw job. What is the recommended sealant that does not bond?

Www.solocoastalsailing.co.uk
 
I've just helped Dylan to replace a seacock. The original was sikaflexed on but fortunately I managed to remove it without disturbing the skin fitting, it was very tight. I replaced it successfully using PTFE tape.
 
I have always used sikaflex to seal the valve to the fitting. I would rather have everything sealed well rather than a weep between the two. If you have to renew the valve it might be a good time to replace the fitting also, the extra cost is small for the knowledge its sealed well.
 
There is a much thicker PTFE (proper tape for everything, as someone had it) might do a better job. In the other thread it was suggested to bring a backnut up under the valve to lock it in position, if that was sealed to the thread and the valve, simply done with a ring seal/soft washer it would seal it without compromising valve renewal.
 
I looked into this several years ago as the joints were parallel threaded and needed to be aligned in a specific direction instead of simply tightened on to a soft washer.

I settled on Rocol Oil Seal. I'm pretty certain that's what it is called but the tin is on the boat at present.

The spec. on Rocol's web-site agrees with my memory of the product I bought.

https://www.rocol.com/products/hard-setting-oil-pipe-sealant

ROCOL OILSEAL
Excellent temperature range from -50°C to +200°C.
Resists pressures of up to 138 bar (2000 psi).
Joints sealed remain easy to break and clean.
Sets hard but is flexible enough to resist vibration, thermal expansioncontraction
Shelf life is 2 years (but mine is still after about 4 years)

I also put a thin smear of Sikaflex on top of the joint after assembly as I'm a belt and braces type. I have dismantled a couple of joints after 2-3 years and they came apart easily by slicing the external Sikaflex with a blade and then turning with moderate force.

I used the same method second time around. Some Rocol Oil seal on the thread, spin valve around into correct position, leave to set (can't remember how long, I think I left it overnight) then smear some Sikaflex where the body and thread meet (almost certainly not needed but doesn't do any harm).

I did think about using back nuts to tighten the valves in the correct orientation. Unfortunately, my setup has 90 degree bends between most skin-fittings and valves so there isn't really enough thread to spare and also limited access.
 
Last edited:
BobnLesley said:
Just about to do one when the rain stops, I'll be using PTFE tape. The one that came out - I suspect another bloody Greek-job - had both the seacock/thru-hull threads and the thru-hull's mushroom bedded/sealed with what looks to be silicone.
Click to expand...

I suppose if your fittings have tapered threads or alignment isn't important then tightening with PTFE will work.

Problem I had with PTFE was that my fittings were parallel thread and I also needed to end up with the valve handle in a specific position. Some valves were also 2 inch and I couldn't find soft washers in that size. So Rocol (or Loctite) was a better option.
 
Mistroma said:
I suppose if your fittings have tapered threads or alignment isn't important then tightening with PTFE will work.

Problem I had with PTFE was that my fittings were parallel thread and I also needed to end up with the valve handle in a specific position. Some valves were also 2 inch and I couldn't find soft washers in that size. So Rocol (or Loctite) was a better option.
Click to expand...

Yes PTFE tape is for tapered threads where the joint tightens on to the taper and the tpe only acts as a seal. Its use on parallel threads is just a bodge

Whenever possible parallel threaded joints should be tightened on to a shoulder and a sealing washer. This is not normally possible with valves and skin fittings The solution is, therefore, to tighten onto a back nut with a suitable sealant, preferably not of a strong adhesive type , to seal the threads. This also allows the valve to be orientated for best positioning of the handle.
 
Plum said:
If you use something like Sikaflex 292, as used on the through-hull skin fitting, to seal the threads when screwing the ballvalve on, when it comes to replacing the ballvalve it is usually a hacksaw job. What is the recommended sealant that does not bond?

Www.solocoastalsailing.co.uk
Click to expand...
I used Sika 291, and let the Sika in the threads hold the valves in the right angle for the handle to turn whilst it set. 24 hours later no movement and as others have said I'd rather have a worry-free perfect seal than worry about leaks or movement with PTFE. Also angle-locating backnuts difficult as horrible near-impossible access to some seacocks for spanners. I was changing everything though, through-hulls, valves and hose tails, all in bronze. Do not plan to do that job again in the time I own the boat, not that it was difficult, as I cut off the old mushroom heads from outside the hull with an angle grinder. If I do have a problem I'll just cut and replace again.
 
I've always used ptfe tape on these connections without backnuts. Probably tapered on parallel threads too. Not suffered from leaks but maybe I've been lucky. As for handle orientation, there's usually scope for cranking it up a bit more till it's in the right position.
 
ghostlymoron said:
I've always used ptfe tape on these connections without backnuts. Probably tapered on parallel threads too. Not suffered from leaks but maybe I've been lucky. As for handle orientation, there's usually scope for cranking it up a bit more till it's in the right position.
Click to expand...

Me too, sufficient PTFE allows alignment.
 
I am surprised a number of replies report success using PTFE tape on these parallel threads. PTFE tape has worked for me too in the past and thought i had just been lucky but i now know i am not alone. Will certainly use a back nut to assist in locking the position.

Www.solocoastalsailing.co.uk
 
Plevier said:
Loctite 572 made for the purpose http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802627158017
Click to expand...

I have used this extensively on all my ball valve to skin fittings and to the raw water strainer and on fuel fittings. It allows perfect alignment to be made and once it has set can be undone with normal hand tools but is more than strong enough to resist any movement during normal use. it also doesn't result in stay strands of PTFE tape ending up where it shouldn't!
 
I followed the YouTube video instructions from Forespar - Sikaflex 291 on the mushroom and under the spreader pad, pre fit the assembly to gauge getting the handle where required. Then I pulled the fitting up into position using an old backing nut, this was then removed, a decent wrap of ptfe following the direction the thread does up, then applied the Marelon valve without any wet sealant.

No leaks yet after 5 days afloat.

i was a bit nervous about having no locknut on the skin fitting, and not sure I would remove the valve afloat, but they provide a suitable hung to allow this to be done.
 
I have always used water pump grease - it's thick grease, like tallow and never weeps. It makes it possible to undo the fitting in the future if needed, as it stops it seizing and it won't weep if you move either of the fittings (unlike silicon or a lot of traditional sealants - once you break the bond they no longer seal).
 
You must log in or register to reply here.

Share this page

Top