Different Types of Ball-Valves

As you might know, a ball-valve is what controls the flow of water into a cistern and it works by a ball, made of either plastic or metal, floating on the surface. This ball is what opens and shuts off the supply of water, depending on water levels. There are different types of ball-valves and which one to use depends on the water pressure in question. The three main types of ball-valves are diaphragm ball-valves, equilibrium ball-valves and piston ball-valves. In this article I will tell you a bit more about these.


Diaphragm Ball-Valves

These types of ball-valves were developed as a solution to overcome the quite noisy piston type ball-valves. There is no moving piston in these ball-valves but instead – a rubber diaphragm. The rubber diaphragm closes over a type of nylon seating at the end of the float arm movement. You can buy them in either brass or plastic depending on how much you want to spend.

Equilibrium Ball-Valves

Just like diaphragm ball-vales were developed to overcome an issue, so were the equilibrium ball-valves. The issue in this case being the ‘water hammer’ created when ball-valves are shutting off too fast. The flow of water is operated by the movement of the float arm. This means that the pressure of the water in the mains pipe cannot open the valve. However, once the valve is open, it is balanced by an equal water pressure on both sides of the piston.

Portsmouth ball-valve

Piston Ball-Valves

This is the simplest type of ball-valves and comes in different designs. One of these designs is the Croydon. It works by a vertical falling piston that goes against a nozzle but as it happens, this design is more or less outdated. Another type of design is the Portsmouth which is normally found in domestic properties. In this design, the float arm closes over a horizontal piston which is fitted with a washer and sits against the valve seating. The main negative with this design of piston ball-valves, is that they are noisy when in use so silencer tubes used to be fitted to them but they are no longer allowed.

Equilibrium/Diaphragm Ball-Valves

A good solution that combines the best qualities of the equilibrium ball-valve and the diaphragm ball-valve is the well-named ‘Equilibrium/Diaphragm ball-valves’. These types of ball-valves are also known as the Torbeck and they combine equal water pressure with the closing of the diaphragm. Torbeck ball-valves are quiet, compact and best of all – maintenance free!


Cistern ball-valves of all types are fitted with a BSP screwed inlet and this is for the tap connector. New regulations state that they have to be adjustable and it is because of this that the Portsmouth version is no longer in use.

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