There are several different types of stoptap and isolating valves used in the plumbing around your home. If you plan to undertake any plumbing jobs, it is useful to know the different types and where in the plumbing system they are used.
A tap with a valve and washer system which is place in a mains-pressure supply pipe. Opening and closing the tap controls the flow of water through the mains pipe. In a working plumbing system the stoptap is usually left open, only being closed when you need to drain and work on the internal system. It is important to fit the stoptap in the correct way, with the arrows showing the flow direction.
Gate valves differ from stoptaps in that they are generally used on lower pressure pipes, such as those leading from a storage cistern. Turning the wheel handle will raise or lower a metal plate (the Gate) to stop or allow the flow of water. Gate valves can be fitted either way around (you don’t need to worry about flow direction). The seal on a gate valve is not as watertight as a stoptap, which is why they are not used on high pressure pipes.
A drain valve is a tap without a handle, requiring the use of a drain valve key to open and close the valve. Drain valves are normally kept closed, only being opened when part fo the plumbing system it is attached to needs to be drained. The ribbed outlet is designed to fit inside a hose, making draining the system easier. Drain valves are usually fitted only to part of the plumbing system when draining through household taps is not possible, such as the central heating system or the rising main.
This is a small isolating valve opened and closed by turning the screw in the middle of the valve. Turning the screw moves a pierced plug to stop or allow water flow. You will usually find service valves directly below kitchen and bathroom taps as a method to isolate them if repairs or replacements are needed. You may also find them on other low pressure pipes around the home and a similar style of valve will be found on the supply pipes for washing machines and dishwashers.