Lockshield Valve

[Doc M]

I noticed that on my rads there is an olive between the TRV and rad connection - but not between the lockshield and rad.

In the past, I have just tightened the nut that connects the lockshield to the rad. Never used PTFE or any sort of jointing compound.

1. So, I was wondering, what makes for a watertight seal? Is it because the threads are tapered?

2. Is it good practice to use PTFE on the threads on the lockshield? Or jointing compound?

3. What does jointing compound actually do? Does it lubricate the threads to make for easier tightening or does it make for a watertight seal or both?

I've been wondering about this for a while! Hope you can help. :help:

Cheers - Martin.

 

[Dan Robinson]

It's a union. Nothing is needed to make the seal. The smooth faces of the metal on the rad tail and the valve do the job.

 

[muggles]

Don't put anything on the threads - they are just there to hold the nut in place. They don't form any kind of seal

 

[Doc M]

Thanks both for posting. Spoke to my plumber this week and he used jointing compound and more recently liquid PTFE on those kinds of unions. I noticed that some of the negative reviews on Screwfix (https://www.screwfix.com/p/flomasta...ect-_-plumbing-_-ptfeliquid&_requestid=185899) mention that they couldn't undo after tightening....

 

[Dan Robinson]

You apply heat if you want to undo them after the PTFE has cured.

Screwfix reviews are often written by muppets.

 

[Doc M]

Thanks for letting me know Dan - much appreciated.

 

[dilalio]

3/4 unions are a bit old hat now but I find them great when you need to remove a rad from fixed pipe tails (with no play) on them... as yours are, coming out the skirting like that. It can be a PITA when you have 1/2 ferrules and olives both ends, protruding into the valve bodies

 

[fixitflav]

So, I was wondering, what makes for a watertight seal?

The end of the rad tail is part of a sphere or similar (male), with a matching part on the valve. Where they meet forms a seal, as others have said. If you have a leak you could apply a very light smear of jointing compound to the rad tail. I use Stag but there are plenty of others. But don't get into the threads or it will make the nut hard to remove.

 

[Doc M]

Thanks for those comments dilalio and fixitflav.