Page 327 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

Chapter 5 Cold water systems

KEY TERM

Water hammer: caused by a
rapid opening and closing
of the float-operated valve.
Washer As the water nears the
Piston water level in the cistern,
the ball valve can begin
Lever arm
to bounce quickly up and
down and from side to side.
This causes the noise to
travel down the pipework,
p Figure 5.95 A BS 1212 Part 1 Croydon-type float-operated valve resulting in reverberation
or a whining noise. It can
BS 1212 Part 2 and 3 (plastic) diaphragm float-operated valves also be caused by a faulty
washer or diaphragm.
These float-operated valves use a diaphragm rather than a washer to control the
flow of water and, unlike Part 1 float-operated valves, they discharge water over
the top of the valve. This makes them less susceptible to being submerged in
water when the overflow runs and so less likely to cause a contamination issue.
They also have fewer moving parts, which makes the valve quieter in operation
and less likely to cause water hammer and reverberation of the pipework.
The main difference between a Part 2 float-operated valve and a Part 3 float-
operated valve is that the Part 2 is made of brass and the Part 3 is made of p Figure 5.96 A BS 1212 Part 2
plastic. They are almost identical in all other respects. It should be noted that diaphragm-type float-operated
plastic float-operated valves are not recommended for cisterns other than WC valve
cisterns because of the risk of freezing and subsequent splitting of the plastic.

BS 1212 Part 4 Torbeck equilibrium diaphragm float-operated
valve
The Torbeck equilibrium float-operated valve is a diaphragm valve that works on
the principle of equal pressure in front and behind the diaphragm when the valve
is open. No moving parts come into contact with the diaphragm. It closes the
valve when a build-up of pressure occurs in front of the diaphragm due to the
float arm closing the pressure relief orifice on the front of the valve. Although
quieter in operation than other float-operated valves, the positive ‘snap’ closing
action can lead to problems of banging and reverberation in some systems.
The valve can be used on either high or low pressures by the insertion of either
a low-pressure or high-pressure flow restrictor in the valve stem. Some valves p Figure 5.97 A BS 1212 Part 4
also have a filter, to filter out any minute solid impurities in the water, which Torbeck-type float-operated valve
could cause malfunction.

The Torbeck valve must be used only on WC cisterns.

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