MJN Plumb & Tile DIY Plumbing

able to identify and stop any water leak in the home in the event of an
emergency. This will prevent unnecessary damage to building fabric and
save punitive emergency call out fees from the professional plumber. The
expectation is that with feedback from the visitors to this page the
information offered will grow.
Overview of a common domestic plumbing system
Mains water is supplied to the building from a centralized supplier; this must
be of a good enough quality for direct consumption (potable), and at a
minimum statutory pressure. Once supplied to the building the only outlet
which must carry this water direct from source is the kitchen tap, so
guarantying access to drinking water in the home. In the past it was often
the case that water supply would be interrupted, so storage solutions were
employed as a matter of course. This was done by having a water tank
situated at the top of the building, as a container for mains water (cold
water storage tank). The water in this tank then becomes non-potable, and
can only be used for washing, hot and cold, (to drink this water it must at
least be boiled and possibly filtered first). It is supplied to the various
outlets under the pressure afforded by acceleration due to gravity, and is
therefore termed a gravity feed system. The pressure afforded by gravity
can be calculated broadly by multiplying every10 metres in height from a
source to an outlet by 1, and dividing the answer by 10, to give the answer
in bar.
EXAMPLE: Cold water storage tank in the loft 10 meters from the bath tap;
10 x 1 = 10 divided by 10 = 1bar at the tap.
Domestic mains water pressure is considered good if it is no less than
3-4bar, and can be termed 'high pressure'.
Gravity feed systems can therefore give low pressure cold water to taps and
to vented hot water cylinders. The (normally) copper hot water cylinder
collects water from the cold water storage tank, and is heated directly by an
electrical element (immersion heater), or indirectly by a coiled pipe
containing heated water from a boiler (central heating primary), or both.
When water is heated it expands and if sealed (e.g. by closed hot water taps
or valves), it becomes pressurized. Therefore the hot water cylinder must
be 'vented' or open to the atmosphere. This is done by extending the hot
water supply pipe at the top of the cylinder (which must be horizontal for a
minimum of 450mm before teeing off), up to the cold water storage tank
and bent over the top of the tank (the vent pipe), above the possible water
level in the tank, and left open with no valves in line. Thus giving the heated
water if heated to a high degree, a chance to escape into the cold water
storage tank, preventing rupture (potentially explosive), of the hot water
cylinder or hot water pipes. The vent pipe must be at least 22mm in
diameter and open at all times, and the cold water storage tank must have
at all times an open overflow pipe, of at least 15mm in diameter, it must be
metal and exiting the building to discharge safely i.e. not above a space
where people might be below. In this way if the vent pipe constantly
delivers extremely hot water to the cold water storage tank, the tank which
will become full of dangerously hot water, can't spill over into the interior
of the building raining hot water down on the inhabitants below. The hot
water used for washing, termed 'domestic hot water', is obtained from the
same pipe as the vent pipe, via a pipe taken after the vent tee. Cold denser
water delivered to the bottom of the cylinder pushes the hot less dense
water up and around the system, with pressure afforded by gravity from the
cold water storage tank. Therefore if the cold water feed pipe to the hot
water cylinder is closed by a gate valve, (typically having a red coloured
wheel which when turned clockwise will close the valve), this will cut off
the supply of hot water to the taps and other hot outlets. The valve will be
situated on a pipe leaving the bottom of the cold water storage tank. This
valve will probably be situated alongside an identical valve on a similar pipe,
which supplies cold water to taps and other cold outlets. Closing both of
these valves will stop the water to all hot and cold water outlets, except
the kitchen cold tap and any other cold outlets taken from the mains supply
e.g. the tank feed. All mains supplies will be valved with a traditional
looking stop valve, closing this valve should shut off all mains supplies to the
building. Look for it under a kitchen sink, in the hallway near the front
door, or in the cellar. The pipe feeding the cold water storage tank will also
have this type of valve in line.
The preceding information should not encourage an untrained individual to
have a go at adding to, altering an existing, or commission a new heating
system. Rather it is intended to give people an understaning of how to find
the relevant cut off points within a system, in order to repair outlets or stop
flood caused by sudden damage to a component within that system.
By clicking on the picture links at the top of this page the reader can gain an
appreciation of basic techniques, needed to conduct basic plumbing repairs.