One of our most frequent questions is how to stop “water-hammer” when water has been drawn from a system. First it is important to know how it occurs. The entry of cold water into your tank and toilet cisterns is controlled by a “ball valve”. As hot water is drawn from your emersion, so cold water rushes in from the cold tank to replace it. When you flush the loo, the same thing happens in your cistern. The incoming flow is regulated by a float, which rises with the water to shut off the valve when the tank is full. This float is generally in the form of a plastic ball on the end of an arm.
When the mains cold rushes into the tank/cistern it causes ripples on the surface, the float bobs about, opening and closing the valve. It is this vibration within the valve and on the float arm which, when reverberating along the pipe, initiates the cause of water-hammer. The velocity of the water flowing through the valve means that when it is shut there is a build up of pressure behind the valve, as more water tries to push on through the pipe. This increase in pressure causes a pressure wave to form which travels back down the pipe. The wave then travels up and down the pipe until the energy is dissipated through friction, this is why there is a ‘hammering’ effect.
There are a few ways to ease this problem, “professional” ways and DIY ways, none are difficult, but the first thing to make sure of is that wherever a pipe is up against a joist, rafter or other surface, it is fixed securely. The first and most effective professional way is to install an equilibrium valve instead of the standard valve in your tank or cistern.
This valve works by allowing some water to get at the back of the piston washer to stop the arm jumping about. The noise reduction valve above it is a further alternative, this allows incoming water to disperse below the water line and reduces the “waves”, it slows the vibration down but most often will not stop it. The cost of a noise reduction valve is about £7.00, with arm and ball and an equilibrium valve is approx £33.00. The noise reduction valve does make a considerable difference to the noise your system makes when filling up.
The DIY way is very effective but slightly cumbersome. Take an ordinary yoghurt carton and attach it to your float arm with some galvanised or stainless steel wire, which will not rust. Suspend the carton just below the water line. When full of water it has enough weight to stop the vibration, but not too much to stop the arm lifting gently.
If your pipes are not hammering but just making creaking noises, this is normally caused by the friction of the pipe moving on the joist or rafter. Get some heavy duty polythene and fix it between the two surfaces and reduce the friction.