Unknown valve

[the watchman]

My father in law has an old oil heating system about 30 years old.

A valve is leaking on the pipework and I'm not sure what it is.

It is situated near the boiler end on the pipe running from the boiler to the cylinder (entering near the top half of the cylinder), which I assume is also the vent pipe as it tees off and carries on up to the attic.

The valve just looks like a tee connection, with the nut on the tee'ed off part having a small hole in it and I can see what looks like a spring underneath it (its quite corroded).

Is this a check valve??

Easy enough to replace?? I think the pipework is 28mm

[the watchman]

Sorry I obviously described where the valve was incorrectly.

Picture the pipe going from the boiler up to the cylinder (which is directly above it) and then the vent pipe tees off which goes up into the attic.

The valve isn't on the vent pipe.

Its at the bottom of this pipe just after it leaves the boiler so before the tee where the vent pipe begins.

[the watchman]

No pic sorry. only saw it today and its in a really inaccessible place (wooden shelving, towels etc).

I will try and get a picture of it.

[unguided1]

sounds like an old safty valve

[the watchman]

What did the old safety valve look like and do.

Is it easy to replace if it was one of these.

[unguided1]

the old style safety valve is pretty well as you described but usually screwed into a brass tee. does it look like this

or this one

[the watchman]

Thanks for that, I now know what it is.

Cheers