The stainless steel check valves are fundamental components for managing the flow direction of fluids as they prevent an inversion from occurring and limit the damage and problems that this phenomenon can cause within the system. These components are widely used within pumps and chemical plants, or applications in which it is necessary to avoid in any way the return of the fluid conducted inside the pipes and there are various types depending on the desired application.
The operating principle behind these devices is simple and is guaranteed by means of a disc, ball or other element bound by a guide and a spring. When the fluid pressure is extremely low or even negative (leading to flow in the opposite direction ), the valve closes and does not allow the passage in the opposite direction to the desired one.When, vice versa, the pressure is high, the valve is open and allows the normal flow of the fluid carried by the pipeline.
The temperatures of use can reach 180 ° C, but also 240 ° C for some particular models, allowing to cover a wide range of applications. Mounting in the correct position (vertical, horizontal or inclined) and the minimum guaranteed pressure are essential characteristics to avoid malfunctions or dangerous instabilities.
The materials with which the check valves are made
The fundamental material for the realization of the check valves is stainless steel, i.e. a steel with a high chromium and nickel content which guarantees both excellent properties from the mechanical point of view and high resistance to corrosion, a fundamental characteristic in this type of applications where there is contact with a fluid and a particularly corrosive environment is generated.
Furthermore, the seal is guaranteed by polymeric or elastomeric materials which have high elasticity and the ability to deform under load, managing to recover their original shape completely and instantly. Among the main ones it is possible to include: - Viton: is an elastomeric material based on FKM, or fluorinated rubber, which has excellent thermal and chemical resistance, as well as high levels of mechanical resistance; - NBR: is the main among the nitrile rubbers and has excellent characteristics from a chemical and mechanical point of view. It also resists aging and low temperatures well, while it is not recommended in high temperature applications; - PTFE: is a thermoplastic and semi-crystalline polymeric material which has a high melting temperature equal to 327 ° C and is therefore suitable for temperature applications. The best known trade name is Teflon (which is the material used for non-stick pans, thanks to the very low coefficient of friction) and has excellent chemical, electrical and wear resistance characteristics.
Check valves and applications
Check valves, as explained in the previous paragraphs, are valves used inside systems to prevent fluids from reversing the direction of flow. In fact, for various reasons that can occur during operation, the flow can slow down and undergo flow reversals that can compromise the system itself: this is resolved with the insertion of a check valve that opposes this tendency.
Some examples of the use of check valves can be given:
- Sewerage discharge systems: as it is easy to imagine, we do not want the flow to occur in the opposite direction with unpleasant consequences for the users;
- Industrial machinery: for example, fluid management systems used during mechanical processing. When a machine works it is often assisted by fluids that reduce friction coefficients and limit heat input. These fluids, once used, must be sent to the correct tank or cleaning station. A reverse flow could compromise the operation of the machine and limit its future functionality.
- Cars: There are numerous check valves in cars. The most common ones concern the fuel line system. The introduction of this component does not allow the flow towards the tank, thus avoiding the emptying of the lines themselves.
- Household appliances: For example, inside washing machines it is possible to find check valves that do not allow the waste water to return inside the drum but only to exit and reach the drain.
- Hydraulic movements: which will be explored in the next paragraph.
Check valves and hydraulic cylinders
In the world of hydraulic movement, cylinders are vital components for operation. Each cylinder has, depending on its characteristic bore, some fundamental properties: among these, we mainly remember the thrust pressure and the pull pressure of the cylinder. However, when working at limit pressures, it may happen that the cylinder does not function correctly due to a slight oil leakage that reduces the characteristic pressure. To compensate for this loss of performance, it is convenient and quick to insert a check valve. This, preventing the occurrence of this condition by limiting the flow in only one direction, allows maximum use of the cylinder pressure.
It is important to underline that the insertion of the valve does not lead to an increase in sustainable pressure, but prevents the maximum pressure value from decreasing. Therefore, although it does not represent an upgrade of the characteristics, it allows not to replace the cylinder with a more performing cylinder, thus avoiding an increase in costs that may not be justified.
