Showers Explained

1.Overflow Pipe: If the FLOAT VALVE fails to shut off incoming water, the overflow pipe leads excess water out of the COLD WATER STORAGE CISTERN and discharges it in a visible position outside the building.

2. Mains Feed Pipe: Supplies the main feed of water to the COLD WATER STORAGE CISTERN.

3. Shower Mixer: The shower mixer should ideally have exclusive water supplies from the COLD WATER STORAGE CISTERN and the HOT WATER CYLINDER via a branch pipe, as here. This will prevent any pressure variations caused by other draw-offs from the same supply. A thermostatic mixing valve has an extra control incorporated to maintain the selected temperature by balancing the hot and cold water. If the flow rate drops on one side, the valve rapidly compensates by reducing the flow on the other side. However, it cannot raise water pressure, so a PUMP is still needed for a more powerful shower.

4. Distribution Pipes: Supply water around the rest of the house.

5. Pump: Here a twin-impeller pump separately pumps the hot and cold water to the SHOWER MIXER. It is usually wired to the ring main by means of a fused connection unit installed outside the bathroom. The pump is activated when the shower valve is operated, and it needs to be located close to the HOT WATER CYLINDER, which should be set to 60°C. A twin-impeller pump can boost other sources, but this is not recommended as operation problems may occur.

6. Hot Water Cylinder: There are two main ways of heating the water in a vented hot water cylinder: either directly via an electric immersion heater, or indirectly by a heat exchanger connected to the heating system — the usual choice when a house is centrally heated by a boiler; an immersion heater provides backup. A dual-coil hot water cylinder is used when solar panels are employed to heat the hot water.

7. Inclined Pipe: Set at around a 45° angle, it will separate most of the air from the water, as the air will rise to the top of the pipe and the water will be drawn off from the bottom.

8. Cold Feed: The cold feed to the HOT WATER CYLINDER should be taken at a position 25mm above the separate cold feed to the shower.

9. Vent Pipe: Heated water expands — it is dangerous to contain it, so a vent pipe is taken from the crown of the HOT WATER CYLINDER via an offset fitting which curves above the COLD WATER STORAGE CISTERN. This vent pipe must not dip in the water.

10. Cold Water Storage Cistern: Located in the loft to create a static head of pressure, the cistern supplies water to the HOT WATER CYLINDER below it and all of the cold water taps in the house, except the kitchen (potable). Old houses may have one of galvanised steel (there are asbestos cylinders in existence); polythene is common in newer properties.

11. Float Valve: Shuts off the flow of water from the MAINS FEED PIPE when the COLD WATER STORAGE CISTERN is full. Here, an arm operated by a plastic or metal ball lies on the surface of the water and rises as the water flows in. When the arm is fully raised, the inlet valve is closed.

12. Waste: A waste outlet should be fitted in the tray with a shallowseal trap. A 40mm waste pipe will run to a hopper or soil stack.

NB: This diagram dissects a gravity-fed (vented) shower system, found in many older homes, with a twin-impeller pump. It is not an accurately scaled and geographic representation for installation use. Most self-builders would install a mains-pressure shower – to be covered in a future issue – unless the water pressure in their area is less than 1.5 bar. By insulating the hot and cold pipes, the rate of temperature change will be minimised.

Further reading:

• Choosing a Shower Enclosure
• A Buyer's Guide to Showers
• A Guide to Bathrooms