Types of Check Valves and Some Precautions
Types of Check Valves and Some Precautions
Check valve is a kind of valve whose opening and closing parts are round disc, and its action is produced by its own weight and medium pressure to block medium backflow. Belong to automatic valve class, also known as check valve, one-way valve, return valve or isolation valve. Check valve the function of this type of valve is to only allow the medium to flow in one direction and prevent the flow in the opposite direction. Usually this kind of valve works automatically. Under the action of fluid pressure flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the fluid pressure and the self weight of the valve disc act on the valve seat, thus cutting off the flow.
1. Lift check valve: vertical check valve and horizontal check valve. The body shape of lift check valve is the same as that of stop valve, so its fluid resistance is large.The disc slides along the vertical centerline of the body. When the medium flows downstream, the valve disc opens by the medium thrust; when the medium stops flowing, the valve disc falls on the valve seat by self vertical.
2. Swing check valve: the disc shape of the swing check valve rotates around the axis of the seat channel. Because the channel in the valve is linear, the flow resistance is smaller than that of the lift check valve, so it is suitable for medium and small diameter, low pressure and large diameter pipelines (large diameter occasions with low flow rate and constant flow change). The sealing performance of swing check valve is inferior to that of lift check valve.
a. Swing check valve is divided into three types: single valve type, double valve type and half valve type. These three types are mainly divided according to the valve diameter, in order to prevent the hydraulic impact from weakening when the medium stops flowing or reverses. Single disc swing check valve is generally suitable for medium calibre occasions. In order to reduce water hammer pressure, it is better to use slow closing check valve which can reduce water hammer pressure when single disc swing check valve is selected for large diameter pipeline. Double disc swing check valve is suitable for large and medium diameter pipeline. It is a fast developing check valve with small structure and light weight; Multi disc swing check valve is suitable for large diameter pipeline.
b. The installation position of swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines.
3. Butterfly check valve: straight through type. Butterfly check valve structure is similar to butterfly valve. It has the advantages of simple structure, small flow resistance and low water hammer pressure. A check valve in which the disc rotates around a pin in the seat. The disc check valve has a simple structure, which can only be installed on the horizontal pipeline with poor sealing performance.
4. Diaphragm check valve: there are many kinds of structural forms, all of which use diaphragm as the opening and closing parts. Due to its good waterproof hammer performance, simple structure and low cost, it has developed rapidly in recent years. But the temperature and pressure of diaphragm check valve are limited by the diaphragm material.
The diaphragm check valve is suitable for the pipeline prone to water hammer. The diaphragm can well eliminate the water hammer caused by medium countercurrent. It is generally used in the low-pressure and normal temperature pipeline, especially for the water pipeline. Generally, the working temperature of the medium is between - 12 ℃ and 120 ℃, and the working pressure is less than 1.6Mpa. However, the diaphragm check valve can achieve a larger diameter, and the maximum DN can reach more than 2000mm;
Key points for check valve:
1. As the check valve is easy to be damaged, the check valve should be installed near the pump outlet. A shut-off valve (generally ball valve or gate valve) is set on the top of the check valve to facilitate maintenance.
2. The medium of check valve on the vertical pipe flows from bottom to top.
3. During installation, pay attention to the direction of medium flow should be consistent with the direction of arrow on the valve body.
Type selection according to nominal diameter:
For high and medium pressure check valves with DN < 50, vertical lift check valve and straight lift check valve should be selected;
Butterfly check valve, vertical lift check valve and diaphragm check valve should be selected for low pressure check valve with DN < 50;
For 50 < DN < 600 high and medium pressure check valve, swing check valve should be selected;
For 200 < DN < 1200 medium and low pressure check valve, the ball check valve without wear should be selected;
Butterfly check valve and diaphragm check valve should be selected for low pressure check valve with 50 < DN < 2000;
Slow closing swing check valve and slow closing butterfly check valve should be selected for the pipeline with small water hammer impact or no water hammer when it is required to be closed.
1. Lift check valve: vertical check valve and horizontal check valve. The body shape of lift check valve is the same as that of stop valve, so its fluid resistance is large.The disc slides along the vertical centerline of the body. When the medium flows downstream, the valve disc opens by the medium thrust; when the medium stops flowing, the valve disc falls on the valve seat by self vertical.
2. Swing check valve: the disc shape of the swing check valve rotates around the axis of the seat channel. Because the channel in the valve is linear, the flow resistance is smaller than that of the lift check valve, so it is suitable for medium and small diameter, low pressure and large diameter pipelines (large diameter occasions with low flow rate and constant flow change). The sealing performance of swing check valve is inferior to that of lift check valve.
a. Swing check valve is divided into three types: single valve type, double valve type and half valve type. These three types are mainly divided according to the valve diameter, in order to prevent the hydraulic impact from weakening when the medium stops flowing or reverses. Single disc swing check valve is generally suitable for medium calibre occasions. In order to reduce water hammer pressure, it is better to use slow closing check valve which can reduce water hammer pressure when single disc swing check valve is selected for large diameter pipeline. Double disc swing check valve is suitable for large and medium diameter pipeline. It is a fast developing check valve with small structure and light weight; Multi disc swing check valve is suitable for large diameter pipeline.
b. The installation position of swing check valve is not limited. It can be installed on horizontal, vertical or inclined pipelines.
3. Butterfly check valve: straight through type. Butterfly check valve structure is similar to butterfly valve. It has the advantages of simple structure, small flow resistance and low water hammer pressure. A check valve in which the disc rotates around a pin in the seat. The disc check valve has a simple structure, which can only be installed on the horizontal pipeline with poor sealing performance.
4. Diaphragm check valve: there are many kinds of structural forms, all of which use diaphragm as the opening and closing parts. Due to its good waterproof hammer performance, simple structure and low cost, it has developed rapidly in recent years. But the temperature and pressure of diaphragm check valve are limited by the diaphragm material.
The diaphragm check valve is suitable for the pipeline prone to water hammer. The diaphragm can well eliminate the water hammer caused by medium countercurrent. It is generally used in the low-pressure and normal temperature pipeline, especially for the water pipeline. Generally, the working temperature of the medium is between - 12 ℃ and 120 ℃, and the working pressure is less than 1.6Mpa. However, the diaphragm check valve can achieve a larger diameter, and the maximum DN can reach more than 2000mm;
Key points for check valve:
1. As the check valve is easy to be damaged, the check valve should be installed near the pump outlet. A shut-off valve (generally ball valve or gate valve) is set on the top of the check valve to facilitate maintenance.
2. The medium of check valve on the vertical pipe flows from bottom to top.
3. During installation, pay attention to the direction of medium flow should be consistent with the direction of arrow on the valve body.
Type selection according to nominal diameter:
For high and medium pressure check valves with DN < 50, vertical lift check valve and straight lift check valve should be selected;
Butterfly check valve, vertical lift check valve and diaphragm check valve should be selected for low pressure check valve with DN < 50;
For 50 < DN < 600 high and medium pressure check valve, swing check valve should be selected;
For 200 < DN < 1200 medium and low pressure check valve, the ball check valve without wear should be selected;
Butterfly check valve and diaphragm check valve should be selected for low pressure check valve with 50 < DN < 2000;
Slow closing swing check valve and slow closing butterfly check valve should be selected for the pipeline with small water hammer impact or no water hammer when it is required to be closed.
