A check valve is a valve whose switching parts are disc-shaped and rely on their own weight and medium pressure to produce the effect of stopping the medium from flowing back. It is an automatic valve, also known as a one-way valve, check valve, backflow valve, or isolation valve. The commonly used check valves are as follows.
Swing check valves have a disc-shaped valve flap and rotate around the axis of the valve seat channel. Because the internal passage of the valve is streamlined, the flow resistance is higher than that of a lift check valve. Small size, suitable for medium, small diameter, low pressure, and large diameter pipeline (large diameter case flow rate is low and infrequent flow changes). Sealing performance is not as good as lifting type.
1. Swing check valve is divided into three types: single valve, double valve, and multi-flap type. These three types are mainly divided according to the diameter of the valve. The purpose is to prevent the media from stopping or backflowing and to reduce the hydraulic shock. Single-valve swing check valves are usually used in medium diameter applications. When a single-valve swing check valve is used for large diameter pipelines, it is best to use a slow-closing check valve in order to reduce water hammer pressure. Double-flap swing check valves are suitable for medium and large-diameter pipelines. Buttress double-flap swing check valve, small structure, lightweight, is a fast developing check valve; multi-flap swing check valve is suitable for large diameter pipeline.
2. The installation position of the swing check valve is not restricted, it can be installed on horizontal, vertical, or inclined pipelines.
Both vertical and horizontal. The body shape of the lift check valve is the same as the globe valve, so its fluid resistance is larger. The valve flap slides along the vertical centerline of the valve body. When the medium flows downstream, the valve flap is opened by the thrust of the medium. When the medium stops flowing, the valve flap will fall on the valve seat due to self-trapping.
Vertical lift type check valve. The direction of the media inlet and outlet channels is the same as the direction of the valve seat channel, and its flow resistance is less than that of the straight-through type. A vertical lift check valve is installed in the vertical pipeline.
Vertical lift check valves can only be installed in horizontal piping. Restricted by the installation requirements, it is usually used in DN <50 small diameter occasions.
The structure of the butterfly check valve is similar to the butterfly valve. The structure is simple, the flow resistance is small, and the water hammer pressure is small. Check valve, valve flap so that the valve flap rotates around the pin in the valve seat. Disc check valve structure is simple, can only be installed in the horizontal pipeline, poor sealing performance.
There are a variety of structural forms, all using the diaphragm as the opening and closing parts, due to its good water hammer performance, simple structure, low cost, in recent years the development of faster. But the diaphragm checks valve temperature and pressure by the diaphragm material restrictions.
The diaphragm check valve is suitable for easy to produce water strikes on the pipeline, the diaphragm can well eliminate the water strikes generated by the media backflow, it is generally used in low-pressure room temperature pipeline, especially for water pipelines, the general medium working temperature between -12 - 120 ℃, working pressure <1.6MPa, but the diaphragm check valve can be larger diameter, DN can reach a maximum of 2000mm or more.
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