When to Change Your Old Cistern
Cold-water storage, within the home, usually situated in the, provides a reservoir of water which equalizes the ‘pull’ on the mains and provides against any reduction or shut down of the main supply. Modern cisterns are made of lightweight materials, and are easy to handle and fit. Different households needs are met by a variation in size of cistern.
Storage cold water (known as potable water) enables a reservoir of water to be stored in the home against the shut down, for any reason, of the mains supply. It also reduces the mains demand, at any given time, by meeting most of the domestic water needs at a constant rate from a storage source.
Traditionally, cold cisterns consisted of galvanized metal, a material likely to corrode. Electrolytic action-a chemical reaction in hard-water conditions-and the build up of lime scale may lead to the constriction of outlet pipes and deterioration of the actual storage vessel.
PVC and GRP
The modern approach is to replace old storage cisterns with either PVC or glass-fibre (GRP) cisterns. Some types of PVC cistern can be folded up and trussed with rope to permit access to a fairly small loft opening. All plastic cisterns have the advantage of being light to handle.
The cold storage cistern is usually placed in the loft. Because it is fairly bulky, it is not easily situated elsewhere in the home. Also, the noise of running water, as the cistern fills, becomes less of an annoyance. The loft, in addition, provides a high point to create static head or pressure, necessary to ensure a strong flow at outlets.
Storage cisterns usually have a capacity of between 230 litres and 365 litres. This depends, of course, on the demand for water of the particular home. A typical, three-bedroomed household, with a family of four, normally requires a minimum water-storage capacity of 230 litres.
An old metal cistern can sometimes present a problem of disposal. It may originally have been put in before the roof was completed-or slates or tiles may have had to be removed to install it. If you have to take out the old cistern, you may have to cut it up with a metal sheet saw. Often, the best solution is to disconnect it, drain it down and move it into the corner of the loft, where space allows, and forget it!
Ancient galvanized or lead piping, often corroded or scaled, may require replacement, and the opportunity can then be taken to replan the plumbing layout, if need be. The cistern can be repositioned if this improves the pipework arrangements.
The modern cistern is often, and wrongly, called a ‘tank’. A tank is a vessel sealed from pressure of the atmosphere, though this is the form of older storage vessels.
Storage cisterns are supplied from the rising main, usually by copper or stainless-steel pipe of 15mm nominal bore or 10mm-bore pipe if in uPVC plastic.
Inlet supply is controlled by a ball valve, which shuts off water by means of an arm operated by a plastic or copper ball, called a ‘float’. This lies on the surface of the water and rises as the water flows in, raising a lever arm, which closes the inlet valve at a determined level.
There are two types of ball valve-high pressure, and low pressure. The high-pressure valve has a smaller water outlet than the low-pressure type. If you use a high-pressure valve where supply is from a storage outlet, filling a cistern may take an indeterminate length of time. Mains supply is always at high pressure.
The low-pressure valve is similar to the high-pressure type but with a larger outlet. This is used on toilet cisterns, which are fed from the outlet or low-pressure side of the storage cistern.
A useful refinement is a gate valve in the rising-main supply to the cistern. If the cistern has to be isolated for any reason it can be shut off without affecting supply of fresh water at the kitchen sink.
Dependent on household needs, one or two feed pipes may be taken from the cistern. One may serve the cold make-up supply to the hot-water cylinder, while the other meets the needs of wash handbasins, baths and bidets.
These outlet pipes are normally adequate if plumbed in 22mm pipe. However, if there is a continuing high demand for hot water, a 28mm pipe can be provided to supply the hot cylinder.
The other essential pipe is the overflow. This has to be a size larger than the inlet supply and usually has a diameter of 22mm.
10. November 2011 by admin
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