Views:90 Author:Site Editor Publish Time: 2020-01-14 Origin:Site
Check valve is a kind of valve whose opening and closing parts are round disc and whose action is generated by its own weight and medium pressure to block the backflow of medium. It belongs to automatic valve, also known as check valve, return valve or isolation valve. The check valve is an automatic valve, and its main function is to prevent the medium from flowing backward, to prevent the pump and the drive motor from reversing, and to release the container medium.
Check valve can be divided into three types: swing check valve, lift check valve, disc check valve, pipeline check valve and pressure check valve according to its structure and installation. Let's talk about their installation in detail.
The disc of the swing check valve is in the shape of a disc, rotating around the shaft of the valve seat channel. Because the internal channel of the valve is streamlined, the flow resistance is smaller than that of the lift check valve. It is suitable for low flow rate and large caliber occasions with little flow change, but it is not suitable for pulsating flow, and its sealing performance is inferior to that of the lift check valve. The swing check valve is divided into three types, single disc type, double disc type and multi half type. These three types are mainly divided according to the valve diameter. The purpose is to prevent the hydraulic impact when the medium stops flowing or flows backward.
It is a check valve with the disc sliding along the vertical centerline of the valve body. Lift check valve can only be installed on the horizontal pipeline, and the disc can be a ball on the high-pressure small caliber check valve. The body shape of lift check valve is the same as that of stop valve (It can be used in common with stop valve), so its fluid resistance coefficient is large. Its structure is similar to the stop valve, and the valve body and disc are the same as the stop valve. The upper part of the disc and the lower part of the bonnet are processed with a guide sleeve. The guide sleeve of the disc can freely rise and fall in the guide sleeve of the disc. When the medium flows in the same direction, the disc is opened by the medium thrust. When the medium stops flowing, the disc falls on the valve seat by the self suspension, which plays a role in preventing the medium reverse flow. The direction of medium inlet and outlet channel of straight lift check valve is perpendicular to that of valve seat channel. The direction of medium inlet and outlet channel of vertical lift check valve is the same as that of valve seat channel, and its flow resistance is smaller than that of straight lift check valve.
Its disc rotates around the pin shaft in the valve seat. The disc check valve is simple in structure and can only be installed on the horizontal pipeline with poor sealing performance.
Its disc slides along the center line of the valve body. Pipeline check valve is a new kind of valve. It has small volume, light weight and good processing technology, which is one of the development directions of check valve. However, the fluid resistance coefficient is slightly larger than that of swing check valve.
This valve is used for boiler feed water and steam cut-off. It has the comprehensive functions of lift check valve, stop valve or angle valve.
In addition, there are some check valves that are not suitable for pump outlet installation, such as bottom valve, spring type, Y type, etc.
① Do not allow the check valve to bear the weight in the pipeline system. The large check valve shall be supported independently, so that it is not affected by the pressure generated by the pipeline system.
② During installation, the direction of medium flow shall be consistent with the direction of arrow marked on the valve body.
③ Lift type vertical disc check valve shall be installed on the vertical pipeline.
④ The lift horizontal disc check valve shall be installed on the horizontal pipeline.
The reason for the disc breaking is that the medium pressure before and after the check valve is in a state of close balance and mutual "sawing". The disc often beats with the valve seat, and the disc made of some brittle materials (such as cast iron, brass, etc.) is broken. The prevention method is to use the check valve with the disc made of ductile materials.
The reasons for the backflow of media are two types.
① The sealing surface is damaged.
② Impurities are entrained.
Repairing the sealing surface and cleaning impurities can prevent backflow.