Stop-valves, gate-valves and ball-valves
Stop-valves, gate-valves and ball-valves are all plumbing fittings that in different ways do precisely the same thing, which is to regulate the flow of water through pipes. Each of the three types of valve performs an important function in your water system, and it is therefore in your interest to know not only what they do and how they do it, but also how to put right any of the faults to which they are prone.
Stop-valves
Your main stop-valve is perhaps the single most important plumbing fitting in your house. In the event of almost any plumbing emergency the very first thing that you should do is turn it off. This will stop the flow of water into your house and reduce the extent of any damage. Looking like a very basic brass tap, your main stop-valve will be found set into the rising main not far from the point where this pipe enters your house. Often it will be located under the kitchen sink. If your house is fairly old then it could be that it won’t be provided with a main stopvalve. If this is the case, then you will have to use the local water authority’s stop-valve instead. You will find it under a hinged metal flap set into your garden path or the pavement outside your property.
This sort of stopvalve usually has a specially-shaped handle that can only be turned with one of the water authority’s turnkeys. So that you can deal promptly with any emergency you should make sure that you either have one of these turnkeys, or at least that you have ready access to one. However, both for the sake of convenience and because specialist gadgets like turnkeys have a habit of disappearing when they’re most needed, you may decide to install a main stop-valve yourself – not a difficult task if the rising main is made of copper pipe.
The internal construction of a stop-valve is identical to that of an ordinary tap, and so it is prone to the same types of faults. But one further trouble that may afflict your stop-valve – which doesn’t crop up with ordinary taps – is that of jamming in the open position as a result of disuse. It’s a problem cured simply by applying penetrating oil to the spindle. However, you can prevent this happening by closing and opening the stop-valve regularly, and by leaving it fractionally less than fully open – a quarter turn towards closure will do.
Gate-valves
Gate-valves Whereas stop-valves are always fitted to pipes that are under mains pressure, gatevalves are used on pipes that are only subject to low pressure. They are therefore found on hot and cold water distribution pipes and on those of the central heating system. Gatevalves differ from stop-valves in as much as they control the flow of water through them, not with a washered valve, but by means of a metal plate or ‘gate’. You can distinguish them from stop-valves by the fact that their valve bodies are bigger, and by their wheel as opposed to crutch – handles. Due to the simplicity of their internal construction gate valves require little attention.
Unlike stop-valves, which have to be fitted so that the water flowing through them follows the direction of an arrow stamped on the valve body, you can install a gatevalve either way round. Mini stop-valves Mini stop-valves are useful little fittings that you can insert into any pipe run. Their presence enables you to re-washer or renew a tap or ball-valve (see below) or repair a water-using appliance such as a washing machine without disrupting the rest of your water system.
They can also be used to quieten an excessively noisy lavatory flushing cistern that is fed directly from the rising main, since by slowing down the flow of water to the ball-valve you can reduce the noise without materially affecting the cistern’s rate of filling after flushing. You usually fit a mini stop-valve immediately before the appliance that it is to control; and they can be turned off and on either with a screwdriver, or by turning a small handle through 180°.
Ball-valves
Ball-valves are really just self-regulating taps designed to maintain a given volume of water in a cistern. While there are a number of different patterns they all have a float-not necessarily a ball these days – at one end of a rigid arm which opens or closes a valve as the water level in the cistern falls or rises. There are basically two types of ball-valves: the traditional type, generally made of brass, in which the water flow is controlled by a washered plug or piston; and the type that has been developed more recently in which the flow is controlled by a large rubber diaphragm housed within a plastic body.
Croydon and Portsmouth ball-valves
The oldest of the traditional types of ballvalves is the Croydon pattern. You can easily recognise one of these by the position of its piston, which operates vertically, and by the fact that it delivers water to the cistern in two insufferably noisy streams. Due to their noisiness, Croydon valves are now by and large obsolete, and if you do come across one you will almost certainly want to replace it.
The traditional type of valve that superseded the Croydon pattern was the Portsmouth valve. You can distinguish it from the former type by the fact that its piston operates horizontally; and as it is still popular with plumbers despite the development of more sophisticated diaphragm type valves, it is a pattern that you may well find in your home. When one of your ball-valves goes wrong the first thing you will notice is water dripping from an outside overflow pipe.
If the valve is a Portsmouth pattern then it is likely to have developed one of three faults. First, it could have jammed partially open as a result of the build-up of scale or the presence of grit; or, secondly, it could need re-washering. In either of these cases this will necessitate you turning off the water supply so that you can either clean the ball-valve or fit a new washer to it.
Lastly, the valve could have been incorrectly adjusted to maintain the proper water level in the cistern – which should be about 25mm (1 in) below the overflow pipe. Even modern Portsmouth valves are rarely provided with any specific means of adjusting the water level, so if you need to do so you will have to resort to bending the float arm. Noise can be a problem with Portsmouth valves. It is caused either by the inrush of water through the valve nozzle, or by vibration created by the float bouncing on ripples on the surface of the water (‘water hammer’).
As silencer tubes are now banned by water authorities, you will have to try other methods to deal with this problem. Reducing the mains pressure by closing the rising main stopvalve slightly may help, and as vibration can be magnified by a loose rising main it is worth making sure that this pipe is properly secured with pipe clips. Another measure the plumbers can take, is the use of a stabiliser for the float using a submerged plastic flowerpot tied to the float arm with nylon cord.
However, if all the above measures fail you will have to consider replacing the Portsmouth valve with one of the modern diaphragm types. Diaphragm ball-valves Diaphragm ball-valves, which are also referred to as BRS or Garston ball-valves, were specially developed to overcome the noisiness and inherent faults of the Croydon and Portsmouth valves. Since the moving parts of a diaphragm valve are protected from incoming water by the diaphragm, there is no risk of them seizing up a result of scale deposits; and the problem of noisy water delivery is often overcome nowadays by an overhead sprinkler outlet which sprays rather than squirts the water into the cistern. Should you need to adjust the water level in a cistern fitted with a diaphragm valve, then invariably you can by means other than bending the float arm.
The only problems you are likely to encounter with diaphragm valves are jamming of the diaphragm against the valve nozzle, and obstruction of the space between the nozzle and diaphragm with debris from the main. You remedy these problems by unscrewing the knurled retaining cap and either freeing the diaphragm with a pointed tool or removing the debris.