Float-operated valves — ballvalves — are the simple devices that control the flow of water into cold storage tanks, central heating feed and expansion tanks, and toilet cisterns. Like taps, they are in more or less constant use, so it’s not surprising that problems sometimes occur.
Check the chart shown below for symptoms of faults and their likely causes. Leaking overflows need urgent attention, since what starts as a tell-tale drip can quickly develop into a flood — most overflows can’t cope with a full-scale flow of water (strictly speaking they are only warning pipes). The leak may also give rise to damp problems on the wall below.
IDENTIFYING BALLVALVE FAULTS
|Valve lets water by, causing overflow:||Washer/diaphragm worn
Seat cracked by frost
Valve mechanism jammed due to scale
Valve corroded due to dezincification
Service valve or replace
Empty float and seal or replace
Replace valve with dezincification-resistant type
|Valve won’t let water by, causing tank to empty:||Valve jammed due to lack of use (very common on C.H. feed and expansion tanks)||Service valve|
|Tank slow to fill||Valve outlet blocked with grit
Wrong seat or valve
Replace seat or valve
|Excessive noise from valve a tank fills||Wrong seat or valve
Water hammer due to high pressure
Float bounding on surface of water
|Replace seat or valve
Service or renew valve
Turn down pressure or fit different valve
Fit damper to float
Before you start a repair of your broken ballvalve, identify what sort of valve you are dealing with (see below) and make sure that the shops are open — you may have to take the valve with you to get replacement parts. Don’t forget that the water will have to stay off in the meantime.
TYPES OF BALLVALVE
All ballvalves work on the same basic principle: an air-filled float, attached to the valve via an arm, rises and falls with the water level in the tank.
Attached to the arm inside the valve is a plunger and plastic diaphragm (diaphragm type), or a piston with a rubber washer (piston type), which closes off the