Check valves are generally used in pipes and other similar devices or equipment to enable the materials or fluids to flow in only one direction while preventing a reverse flow from happening. Although this control valve comes in different forms, sizes, and functions, they typically operate on the same principle. Likewise, most of these valves have 3 common parts or components:
1. The inward port that allows entry to the material (gas or liquid).
2. The body through which the material passes.
3. The outward port which allows the material to exit the device.
Various technologies are employed to regulate the inward and outward flow of gases and liquids. Although some parts may be similar, these are not interchangeable between types of valve controls as they differ in function, size and materials. Here are various types of technologies used and the components or parts that make the valves work:
Single Disc: This is designed with the closure disc hinged at the top of the cap and can be pushed open by the flow. It automatically closes once the flow reverses. This type of valve is not recommended for applications where flow reversals are frequent because the disc will wear out easily with the constant pounding it will get. The single disc check valve may be set up either in a vertical or horizontal position. However, when it is vertically mounted, there is a tendency for the valve to stay open when there are gradual velocity changes. A lever or a counter balance must be used to neutralize this tendency.
Double Disc or Wafer: This uses 2 half circular discs that are attached to each other. They fold together with forward flow and closes to full circle when there is reverse flow. This is usually installed between two flanges and most commonly used in liquid dispensers. It is popular because it is inexpensive and compact.
Lift Type: Lift type non-return valves have a guided disc. It may be spring loaded that can work whether it is horizontally or vertically installed. If the device has no spring, mounting should be done in such a way that gravity will enable the disc to close. This is commonly used for granular liquid dispensers.
Ball Type: This uses either a spring loaded or a free floating ball nestled on a seat that serves as the closure component. When the flow reverses, the ball settles back to its seat to prevent the back flow. This is one of the most popular types and mentioned in any check valve selection guide. It can be used in most applications and will work even for liquids that leave sticky deposits. Because the ball moves freely, there is even distribution of pressure and the valve seat is kept clean.
Silent or Center Guide: These is similar to a lift check valve and has a center guide that extends from the inward port to the outward port. This type features a stopper made of spring and bushing that is specifically designed to minimize noise created by its movements.