There are many different kinds of valves but when it comes to plumbing it is mainly four different ones that are used. These are called drain-valves, gate-valves, servicing valves and stop-valves. You can find them fitted in both hot and cold water supplies and they are used to cut off water from the entire system or if needed, just from individual branches. In this article I will tell you a bit more about two of these valves.
Some valves can fully restrict the flow of water but gate-valves only have the capacity to restrict it slightly when opened. Therefore they are usually fitted to cold supply pipes. You can find them along pipes going from a cold water cistern as the water pressure is lower there. The control mechanism of many gate-valves is typically a solid gate (or portcullis) which is lowered to cut into the water flow when screwed in. Most gate-valves are fitted with wheel-handles and they have to be opened completely open to avoid creating airlocks. They normally come with compression fittings and can be fitted way round. If you come across cold supplies from a cold water cistern that is not yet fitted with gate-valves, you can easily sort this out as it only requires a short length of pipe to be cut out. Rather than having to drain the cistern of water, you can use a cloth and polyethylene sheeting. Bung this up and place it against the outlet. By turning on the taps, the ‘bung’ should seal o the opening. If this does not work or if you so prefer so, you can always use a drain-easy-kit.
The water regulation stipulates that servicing valves should be fitted on pipes leading to ball-valves, or so called float-operated valves, on cold water, feed-and-expansion-cisterns as well as WCs. Most servicing valves that you come across should have a small ball fitted internally with a whole through it and this is so that a quarter turn is all that is needed to fully open or close the valve. This is operated by a small circular knob or by fitting a screwdriver into the slot. Service-valves used for installing washing machines generally have a tee fitting and a lever. It would be advisable to fit servicing valves before every single tap to allow them to be rewashered without having to drain the entire pipe and possibly also the cistern. Always leave a job in the same good state as you want to find your next one in. Best of luck!