Check valve refers to the valve whose opening and closing part is a circular disc and acts by its own weight and medium pressure to block the back flow of the medium. Check valve is an automatic valve, also known as one way valve, cut off valve, non return valve, isolation valve, back water valve, back pressure valve. There are some commonly used check valve as follows:
1. Lift type check valve: lift type check valve has vertical lift check and horizontal lift check valve. The valve body shape of the lifting type check valve is same as that of the globe valve, so its fluid resistance is larger. The disc of the lift check valve rise up and down along the vertical center line of the valve body. When the medium flows downstream, the valve flap is opened by the thrust of the medium, and when the medium stops flowing, the valve disc falls on the valve seat by its own weight;
1.1. For vertical lift check valve, the direction of the medium inlet and outlet channels are the same as that of the valve seat channels.its flow resistance is smaller than that of the straight trough type lift check valve. Vertical lifting check valves are installed on vertical pipelines;
1.2. Horizontal lifting type check valve can be only installed on horizontal pipelines, restricted by installation requirements, horizontal lifting type check valve is often used in pipelines with small diameter DN<50;
2. Swing type check valve: the disc of swing type check valve is disc-shaped and rotates around the shaft of the valve seat passage. Because the passage in the valve is streamlined, the flow resistance is smaller than that of the lifting type check valve. Swing type check valve is suitable for pipelines with small and medium diameter, low pressure and large diameter pipelines(large diameter pipelines with low flow rate and infrequent changes in flow). the sealing performance of swing type check valve is not as good as that of the lift type check valve;
2.1. the swing type check valve is divided into three types: single disc swing check valve, double disc swing check valve, and multi disc swing check valve. These three types of swing check valve are mainly divided according to the diameter of the check valve, to prevent the back flow of the medium, or reduce the flow force impact when the medium is flowing back. Singe door swing type check valve is generally used for pipelines with medium diameter. When the single door swing check valve is used for large diameter pipelines, it is better to use the slow closing check valve to reduce the water hammering pressure; Dual door swing type check valve is suitable for pipelines with large and medium diameter. Wafer dual door swing check valve has small structure and light weight, it is one kind of fast-developing check valve. Multi door swing type check valve is suitable for large diameter pipelines.
2.2. the installation position of the swing check valve is not limited, and swing type check valve can be installed on horizontal, vertical or inclined pipelines.
3. butterfly type check valve is one kind of straight through type check valve. The structure of butterfly type check valve is similar to that of a butterfly valve. Its structure is simple, the flow resistance is small, and the water hammer pressure is small. Butterfly check valve is one kind of check valve whose disc rotates around a pin on the valve seat. The structure of butterfly type check valve is simple, and it can be only installed horizontal pipelines and the sealing performance of butterfly type check valve is poor.
4. Diaphragm check valve: there are various structural forms, and for all of those diaphragm check valves, diaphragms are used as opening and closing parts. Due to its good water-hammer-proof performance, simple structure and low cost, the diaphragm check valve is developing very fast recently. However, the operating temperature and pressure of diaphragm check valve are limited by the material of diaphragm.
Diaphragm check valve is suitable for pipelines that are prone to generate water hammer. The diaphragm can well eliminate the water hammer caused by the reverse flow of the medium. It is generally used in low pressure and normal temperature pipelines, especially for tap water pipelines. Generally, the working temperature of diaphragm check valve is between -12–120℃, its working pressure is PN<1.6MPa. But diaphragm check valve can be made into a large diameter ones, its DN can reach more than 2000mm;
Installation guideline for check valves:
1. Since the check valve is easily damaged, check valve should be installed near the outlet of water pump, and a stop valve( generally a ball valve or a gate valve) should be installed on the upper part of the check valve to facilitate the maintenance.
2. If the check valve is installed on vertical pipelines, the medium should flow from bottom to top.
3. When installing a check valve, make the direction of the medium to be consistent with the direction of the arrow marked on the valve body.