Pneumatic Non Return Valve is actually used in places where the normal check valve is not able to function properly. The activation of the pneumatic valve depends on the fluid pressure. Cracking pressure is the minimum pressure in the upstream section at which the valve operates. There is no resistance to flow of the fluids in the pipes in the normal course of the action. However, when there are situations where the danger of back flow is present, the pressure on the upstream section is increased and at this time, the valve is shut off. In certain cases, the valve may also be shut off using an external handle. Back flow is the flow of the fluid in the direction opposite to the intended direction of flow, which is not at all desirable.
There may be instances where there is chemical wastes flowing from a place. If one were to use the normal check valve the flow from the main pipes could enter the site and the entire thing could lead to contamination. When you are faced with such a situation the pneumatic non return valve is closed with the pneumatic pressure. Depending on the size and the situation the valve may be made of plastic or metal. One could understand the working method of the valve if one sees how the air is filled in the tires of a vehicle. The valve used is a duck bill valve. The flow on the upstream section is made of a soft tube which does not support back flow. Once the air or the fluid is sent into the upstream section, the tube collapses on its own. The pressure is maintained within the upstream section itself. Instead of the duck bill valve one may also use a plastic non return valve or metal valve.
In the case of the plastic valves there is a flap or a disc which remains open when the flow is in the forward direction. Once the flow direction gets reversed, the flap shuts down and the back flow is prevented. In the cases where the flow is in large quantities, the use of inclined disc valves may be advocated. This gives more stability to the flow and ensures the safety of the system.
There are many advantages of the pneumatic non return valve :-
- They are more robust in construction
- They are useful when sealing off an entire section
- They are operable when the normal check valve is not functioning
- They have a long usable lifespan
The use of valves has simplified the daily working routines and helped men in the various processes which are encountered in the fulfillment of his duties. Valves are common place and one will see them in the house also. Since most of the valves are self-operable they do not need any human interference and one barely notices them as one passes by. However, their use is significant and man has always been dependent on the process of regulating the flow and maintaining the direction of flow of the fluid.