A prerequisite of success in virtually any do-it-yourself plumbing project is a sound understanding of the existing plumbing system of the house. The cold water distribution systems, hot water supply systems and above-ground drainage systems in common use in the United Kingdom are described and explained below.
Cold water distribution A communication pipe connects the Water Authority’s water main beneath the highway with the Authority’s main stop-cock, usually situated at the base of a guard-pipe with a hinged metal cover, either just within or just outside the property boundary. From that stopcock the service pipe, which should slope slightly upwards to allow air bubbles to escape, but which must have a soil cover of at least 820mm throughout its length, passes under the footings of the house and rises to the surface, usually within the kitchen or utility room.
A few inches above the floor the service pipe – now usually referred to as the rising main – should have another stop-cock (the householder’s main stopcock) fitted into it. Immediately above this stop-cock should be a drain-cock to allow the rising main to be drained when required.
Older houses, and perhaps some modern ones in rural areas, may have a direct cold water distribution system. With such a system every cold water draw-off point in the house – bathroom and kitchen cold taps and lavatory flushing cisterns – will be connected direct to the rising main. There may be a cold water storage cistern in the roof space or elsewhere, but its purpose will be solely that of supplying water at constant low pressure to a cylinder storage hot water system. On the other hand, there may be no storage cistern at all. Hot water supply may be by means of a multipoint instantaneous gas water heater connected direct to the main.
Indirect cold water distribution systems are usually insisted upon by Water Authorities today, where new buildings are concerned. With such a system only the cold tap over the kitchen sink (plus perhaps a garden and washing machine supply) is connected direct to the rising main. Bathroom cold taps and lavatory flushing cisterns are supplied from a substantial main storage cistern, usually in the roof space, to which the rising main connects through a ball-valve. To check whether your home has a direct or indirect system turn off the main stop-cock, open up the bathroom cold taps and flush the lavatory cistern. If these taps cease to flow immediately and the flushing cistern does not refill, you have a direct system. If the cistern refills and the taps continue to flow, it is an indirect one.
Hot water supply
Hot water supply may, as has already been mentioned, be provided by means of an instantaneous multipoint gas water heater connected direct to the rising main. One or other of the different forms of cylinder storage hot water system are however more common.
With the direct cylinder system a storage vessel, usually a copper cylinder, with a capacity of about 130 litres, is supplied with water from a cold water storage cistern at a higher level, the supply pipe entering the cylinder near its base. From the cylinder’s apex, a vent pipe rises to a level above that of the cistern and is bent over, open-ended, to terminate over it. The distribution pipes to the hot taps are taken from this vent pipe ajbove the level of the cylinder.
Water in the cylinder may be heated solely by means of an electric immersion hea-ter; by means of a (usually solid fuel) boiler or by a combination of both. Where there is a boiler a flow pipe rises from the upper tapping of the boiler to a tapping in the upper part of the cylinder wall. A return pipe simi- larly connects the lower tapping of the cylinder to the lower tapping of the boiler. For as long as the boiler is alight there will be a constant circulation of water between it and the cylinder.
An indirect cylinder hot water system should always be provided where hot water supply is provided in conjunction with central heating and is advisable in areas with a hard or corro-sive water supply, even where central heating is not to be provided.
Water stored in an indirect cylinder is heated by a closed coil or heat exchan-ger to which the flow and return pipes from the boiler are connected. This circulation between boiler and heat exchanger is called the primary circuit. It is supplied with water from a small feed and expansion tank in the roof space and has its own vent pipe which terminates openended over this small tank.
There are also self-priming indirect systems which may be difficult, at first glance, to distinguish from direct hot water systems. Self priming cylinders are fed from the main cold water storage cistern. They contain a patent ‘inner cylinder’ through which water can flow into the primary circuit but is prevented from returning because the design of the inner cylinder produces a massive air lock.
The only certain way to distinguish any indirect cylinder from any direct one is by the way in which the boiler flow and return pipes are connected. Indirect cylinders, both conventional and self-priming, have male connectors projecting from the cylinder walls. Direct cylinders always have female connectors with a thread inside the cylinder.