How to open this old valve?

23 Feb 2011
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United Kingdom
Hello, This 'orrible old 22mm isolation valve is the CH drain-off (pipe on RHS to outside) and needs opening. Do I just turn the top, flat part or do I need to undo/loosen the nut on the bottom first? It's pretty stuck but I haven't used massive brute force yet, just sprayed on some WD40 for all the good it'll do. What sort of valve is it anyway?
Thanks for your help!

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Called a sludge cock. Turn the top a quarter turn to open, it may be stiff.
Thanks. At least I know what I'm swearing at now. Should it turn both ways? Access is really tight so I need to be sure before I lean on it.
What is special about a 'sludge cock'? Can I replace with a standard gate valve?
Be careful when you start to put weight on the valve, it's a tapered plug in a tapered hole so chances are it's seized solid. To much twisting on an unsupported body and you might end up tearing the valve off the pipework. If you can, slightly slacken off the nut under the valve and give the bottom of the stem an upward tap; that might just loosen off the tapered plug.
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Ok, thanks for that. Unfortunately the installers decided to route a rad return pipe directly underneath the valve so there's no way to meaningfully tap the bottom of the stem. Might have to drain down elsewhere and replace this valve. Any reason not to use a standard gate valve?
As above and have a look underneath there will often be a lug on the plug so it only turns one way but easy to see which way it is when you look at it.

PS A sludge cock is just that, it will allow sludge that might block a normal drain valve to flow through freely.
Thanks everyone. It did free off in the end - undid the nut on the bottom then much wiggling and application of Plusgas top and bottom. That stuff really is better than WD40 for freeing things up.

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