There are two basic types of radiator valve that should be fitted to a domestic central heating radiator, the first is generally known as a lockshield valve (or a variation is a wheel head valve) and the second is known as a thermostatic radiator valve.
A lockshield (or wheelhead) is a simply on/off valve and is simply a method of stopping the water flow either too or from the radiator, effectively taking it out of circuit. The lockshield version is designed so that it not easily operated by hand, therefore used only in the event of maintenance of the central heating system. The wheelhead is similar in design but provides a wheelhead to open of close the valve by hand, so isolating or bringing the radiator back in circuit. All radiators are likely to be fitted with at least one lockshield valve
The other type of radiator valve is a thermostatic radiator valve, which is fitted on the opposite end of the radiator to the wheelhead of lockshield. This device has a user dial on it to allow the user to independently control whether hot water flows to the radiator, based on a set of pre-set temperature levels, usually 1 to 5. The dial allows settings from a very low “Frost” setting to a high 5 setting. The valve remains open allowing the flow of water through the radiator until the thermostat detects that the surrounding temperature has been reached at which point it shuts the valve
The lockshield, wheelhead and thermostatic valve are available in both a straight and angled configuration. The valves are fixed to the side of each radiator using the integral female thread and a small amount of PTFE tape, ensuring surfaces are perfectly clean. If the pipework, which supplies the radiator, enters the area vertically from the bottom then angled radiator valves are used and if from the side then straight valves are used. This is the opposite if they are to be used as towel warmer valves, which usually have the valve connections on the underneath rather than the side. Radiator valve extensions are available in various lengths up to about 100mm. These are particularly useful when old imperial size radiators are being replaced with new metric sizes, and often eliminate the need for extensive re-piping by extending the position of the radiator valve entry by a small amount to line up with the existing pipework. There are different types of radiator tail extensions available, some of fixed length and some of adjustable length within a given range.
Thermostatic radiator valves are supplied with white plastic dials as standard but are also available in plastic chrome or more expensive metal. Different types of technology are also available for detecting the shut off temperature, which can drastically affect the price.
Lockshield and wheelhead radiator valves are available to suit 8mm, 10mm, 12mm and 15mm pipe in both angled and straight configuration and thermostatic radiator valves are generally only available to accept 15mm pipe. By the use of a single or three part reducer inserted into the compression housing of the valve body these can be converted to accept 12mm, 10mm or 8mm pipe without the need to use a reducing coupling. Care should be taken when using these reducers as they replace the copper olive and are easily not re-usable
A final note on thermostatic radiator valves is very important and that is there should always be one radiator in any installation without a thermostatic or wheelhead valve fitted. This is because there always has to be one radiator that will stay open no matter what the temperature, so that an over-pressure does not occur within the system.
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