Lockshield &TRV shut. Bleed valve still drips.

[Dysanovic]

Hi, I'm new to this forum so I apologise if I'm not adhering t

etiquette

I'm removing a radiator as I'm doing some decorating. I've turned of

the locksheild valve and I have also set my Thermo valve (Drayto RT212) to the 0/decorators setting

When I open the bleed valve I get a constant drip of water (maybe

drips per min). I've left it drip for quite some time but it doesn' seem to stop. Has anyone else found that it the bleed valve drips lik this once the valves have been seemingly closed

If I were to drain the radiator would I be able to plug the leakin

valve

-- Dysanovic

[Codswallop]

I haven't had this with a radiator valve not shutting off completely but I have known it with other water stop valves. You won't know whether it's the TRV or the lockshield valve until you take the radiator off. You could leave well alone, just put a bowl or tray under the valve during decorating and put the rad back as soon as possible. If it's the lockshield you may find that another slight turn will stop the drips. Or drain the system then replace the leaking valve, refill, add inhibitor, bleed rads etcetera. I'm not sure what you mean by plugging the leaking valve, unless you mean blanking off the valve inlet/outlet by fitting a screw-on end cap. You could do that if you can find an end cap to fit. Did you make a note of the position of the lockshield valve before you turned it off?

[Dysanovic]

Hi Codswallop,

Thanks for the reply. You are spot on, I got a spanner instead of pair of pliers to make sure that the locksheild valve was shut and tha appears to have done the trick. When I undo the bleed theres now little bit of water escaping at first but then nothing, no drips! S now I'm going to drain the radiator.

Yes I made a note of where the locksheild valve was set to. To als make life a bit easy I used a perm. marker to mark one end of th valve, which will visually help when I need to set it back to its ol position.

I'll let you know how the dra> "Dysanovic" wrote:-

-- Dysanovic

[Dysanovic]

Drained the radiator with no real problems. Took about 4 cat-litte

trays until it was empty. Found that the locksheild valve was weepin ever so slightly so I tightened it a little more. Fingers crossed it'l stay shut :s

A questi> Hi Codswallop,

-- Dysanovic

[Aidan Karley]

The point of Teflon tape is to reduce the rotary torque you have to put onto the fitting to get the necessary compressive (longitudinal) force on the metal-to-metal sealing surface of the valve. The tape might help you if you're finding the fitting still leaks after you torque it up to the maximum permitted torque (you do use a torque wrench on the fittings don't you? Didn't think so - I don't think the suppliers even put torque figures on their datasheets. Maximum permitted torque is therefore where your adjustable spanner slips once, starting to round the nut. You don't want to your nuts round.) In normal practice, getting Teflon tape slivers between the surfaces of a metal-to-metal seal is a recipe for leaks. If the metal surfaces are scratched, you might need to look at a joint sealing compound, rubber seal, or something like that. Going down that road is out of my experience for DIY and water - if you're plumbing analytical hydrogen into a laboratory, I can give you some compound names. (NB : Teflon tape is appropriate for root-filling of NPT threads, which seem to be used for radiator taps. But only up to a couple of hundred PSI.) Teflon tape is like WD-40 : for the job it's designed for, it's a good tool ; but it's not designed as a cure-all, panacea, general factotum, miracle-worker or bike repair kit.

[Dysanovic]

Aidan,

Cheers for the very well written reply. As well as PTFE tape having low co-efficient of friction (hence reducing the "the rotary torque yo have to put onto the fitting to get the necessary compressive (longitudinal

force on the metal-to-metal sealing surface of the valve"), it is ca also resist extreme temperatures and it's water tight.

I th> In article [e-mail], Dysanovic wrote:-

-- Dysanovic

[Aidan Karley]

Like I said, I've not much experience of using Teflon tape on water. I guess the hydrophobicity of the Teflon would help it to seal a metal-to-metal surface against water. For analytical gases (and I guess for fuel gases), it's worse than a waste of time, and I can understand why amateurs are not permitted to f*ck with domestic gas systems. The temptation to think "this material makes pipes seal tight, for water, so I'll use it to seal the gas pipes too" is obviously there. It can take a several attempts to beat the idea of never using Teflon tape on gas seals out of novices in the workshop, and some of those I wouldn't trust to plumb up a camping stove, let alone a permanent installation.

[<me9]

There is a (thicker) PTFE tape available for gas use.

[Brian Sharrock]

... easily identied as it's YELLOW! ...