Are these my hot water gate valves?

[davidsmith98]

Just need some advice on what I'm looking at in my loft space. I have a water tank and hot water cylinder (actually, looks like two cylinders next to each other) in our roof space. I'm trying to turn off the hot water to do some work on our shower. I understand that I have to close the gate valve leading from the cold water storage tank to the hot water cylinder? I have attached some pictures, could someone confirm what these gate valves are? There are two of them, but I only need to close one valve? Also, it looks like there are two hot water cylinders next to each other - is that why there are two gate valves? I live in a tenement on the top floor flat. Does that mean one cylinder is for my neighbour? Or is one cylinder for my tap water and the other for central heating?

Any advice appreciated!
Thanks

 

[ianmcd]

One gate valve turns off the cold supply to the HW Cylinder, the other turns off the cold water storage supply, you will have to turn off both to change your shower, if your shower only has one pipe it is an electric shower and neither will turn that off, you need to isolate the cold water mains inlet

 

[davidsmith98]

Ok, thanks for the reply.

Is there anything I need to watch out for when I turn them back on, avoiding air in pipes?

 

[Madrab]

The issue that happens with gate valves like that is depending on how told the valves are or how they have been left that last time, they may be jammed or seized open or they may jam/seize when closed. Unfortunately gate valve can be prone to it, not all of course, just go gently with them.

Sometime it is safer to bung the outlets of the cistern and while doing so change those ones for full bore lever valves.

Gravity systems can be prone to airlocks if there are any upward runs on the pipework as the gravity pressure cant force out the airlock. That can usually be corrected by a hose from the mains and reverse feed from the tap that's airlocked back up to the cistern or down from the feed in the cistern.