OPERATION PRINCIPLE

Check valves mounted on large supply networks and in pumping station delivery lines are required to operate frequently. Statistics show that when serious surging occurs, this is often due to the fact that the incorrect type of valve has been fitted.

The valve then closes under the effect of its weight or a return spring, or by the reversal of the flow. Experience and calculations show that reversal can occur within an extremely short time (from 1/100 to 1/10 of second).

If the valve does not respond quickly, closure will occur sharply during reversedflow conditions, with the result that:
– the disc is force-fully applied against its seating, with the consequent production of a loud shock wave;
– water hammer is produced, with a steep wave front.

Shock waves and water hammer give rise to stresses which may even cause the mechanical failure of the valve’s components.

These problems are even more pronounced if an air-pressurized water tank is incorporated in the system. In this case, flow reversal in the short run of pipeline between the tank and the pump occurs very rapidly. The valve must therefore operate very quickly if serious damage is to be avoided. This is also the case for a pump switch off, when several pumps operate in parallel.
The ideal non-return flap is the one which closes at the same time the flow reverses. For that, the disc must have a short travel and a low mass (low inertia and  frictions)