Butterfly check valve

Butterfly check valve refers to the valve that automatically opens and closes the disc depending on the flow of the medium itself, and is used to prevent the medium from flowing back. It is also called check valve, one-way valve, reverse flow valve, and back pressure valve. The check valve is a kind of automatic valve, its main function is to prevent the back flow of the medium, prevent the pump and the drive motor from reversing, and the discharge of the container medium. Check valves can also be used to supply pipelines for auxiliary systems where the pressure may rise above the system pressure. Check valves can be divided into swing check valves (rotating according to the center of gravity), lift check valves (moving along the axis), and butterfly check valves (rotating along the center).

Function
 
The function of the butterfly check valve is to only allow the medium to flow in one direction and prevent the flow in one direction. Usually this kind of valve works automatically. Under the action of the fluid pressure flowing in one direction, the valve flap opens; when the fluid flows in the opposite direction, the fluid pressure and the self-coincidence of the valve flap act on the valve seat, thereby cutting off the flow.
 
Structural features
 
Butterfly check valves include swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve disc like a door that rests freely on the inclined valve seat surface. In order to ensure that the valve clack can reach the proper position of the valve seat surface every time, the valve clack is designed in a hinge mechanism so that the valve clack has enough space for turning and makes the valve clack truly and comprehensively contact the valve seat. The valve clack can be made of metal, leather, rubber, or synthetic covering can be inlaid on the metal, depending on the performance requirements. When the swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is seated on the sealing surface of the valve seat on the valve body. Except that the disc can be raised and lowered freely, the rest of the valve is like a shut-off valve. The fluid pressure lifts the disc from the seat sealing surface, and the backflow of the medium causes the disc to fall back onto the seat and cut off the flow. According to the conditions of use, the valve clack can be an all-metal structure, or it can be in the form of a rubber pad or a rubber ring inlaid on the valve clack frame. Like a shut-off valve, the passage of fluid through the lift check valve is also narrow, so the pressure drop through the lift check valve is larger than that of the swing check valve, and the flow rate of the swing check valve is restricted rarely. This type of valve should generally be installed horizontally in the pipeline.
 
According to its structure and installation method, the check valve can be divided into:
1. The disc of the butterfly check valve is disc-shaped, and it rotates around the shaft of the valve seat channel. Because the inner channel of the valve is streamlined, the flow resistance is smaller than that of the rising butterfly check valve. It is suitable for low flow rate and non-return flow. Large diameter occasions with frequent changes, but not suitable for pulsating flow, and its sealing performance is not as good as the lifting type. The butterfly check valve is divided into three types: single valve, double valve and multi valve. These three types are mainly divided according to the valve diameter. The purpose is to prevent the medium from stopping or flowing backwards and weaken the hydraulic shock.
2. Butterfly check valve: According to the working form of the disc, it is divided into two types: 1. The check valve with the disc sliding along the vertical centerline of the valve body. The butterfly check valve can only be installed on the horizontal pipeline. A round ball can be used on the disc of the small-diameter check valve. The valve body shape of butterfly check valve is the same as that of globe valve (which can be used in common with globe valve), so its fluid resistance coefficient is relatively 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 valve disc and the lower part of the valve cover are processed with guide sleeves. The disc guide can be moved up and down freely in the valve guide sleeve. When the medium flows downstream, the disc opens by the thrust of the medium. It drops down on the valve seat to prevent the medium from flowing back. The direction of the medium inlet and outlet channels of the straight-through butterfly check valve is perpendicular to the direction of the valve seat channel; the vertical lift check valve has the same direction of the medium inlet and outlet channels as the valve seat channel, and its flow resistance is smaller than that of the straight-through type; 2. A check valve in which the disc rotates around a pin shaft in the valve seat. The butterfly check valve has a simple structure and can only be installed on a horizontal pipeline, with poor sealing performance.
3. In-line check valve: a valve whose disc slides along the centerline of the valve body. In-line check valve is a new type of valve. It is small in size, light in weight, and good in processing technology. It is one of the development directions of check valves. But the fluid resistance coefficient is slightly larger than that of the swing check valve.
4. Compression check valve: This valve is used as a boiler feed water and steam shut-off valve. It has a comprehensive function of lift check valve and stop valve or angle valve.
In addition, there are some check valves that are not suitable for pump outlet installation, such as foot valves, spring-loaded, Y-type and other check valves.

Use and performance specifications:
This valve is used as a device to prevent the backflow of the medium on industrial pipelines.
 
Installation matters
 
The installation of check valve should pay attention to the following things:
1. Do not allow the check valve to bear weight in the pipeline. Large check valves should be independently supported so that they are not affected by the pressure generated by the piping system.
2. When installing, pay attention to the direction of medium flow should be consistent with the direction of the arrow voted by the valve body.
3. Lifting vertical flap check valve should be installed on the vertical pipeline.
4. The lift-type horizontal flap check valve should be installed on the horizontal pipeline.
 
1. Function principle and structure description:
During the use of this valve, the medium flows in the direction of the arrow shown in the figure.
2. When the medium flows in the specified direction, the valve flap is opened by the force of the medium; when the medium flows backward, the sealing surface of the valve flap and the valve seat is sealed due to the weight of the valve flap and the action of the reverse force of the medium. Close together to achieve the purpose of preventing the medium from flowing backwards.
3. The sealing surface of the valve body and valve clack adopts stainless steel surfacing welding.
4. The structural length of this valve is in accordance with GB12221-1989, and the flange connection size is in accordance with JB/T79-1994.
 
Storage, Installation and Use
5.1 Both ends of the valve passage must be blocked, and there is a dry and ventilated room. If it is stored for a long time, it should be checked frequently to prevent corrosion.
5.2 The valve should be cleaned before installation, and the defects caused during transportation should be eliminated.
5.3 During installation, you must carefully check whether the signs and nameplates on the valve meet the requirements for use.
5.4 The valve is installed on a horizontal pipeline with the valve cover upward.
9. Possible failures, Causes and Elimination methods:
1. Leakage at the junction of valve body and bonnet:
(1) If the nut is not tightened or loosened evenly, it can be re-adjusted.
(2) If there is damage or dirt on the flange sealing surface, the sealing surface should be trimmed or the dirt should be removed.
(3) If the gasket is damaged, it should be replaced with a new one.
2. Leakage at the sealing surface of the valve clack and the valve seat
(1) There is dirt between the sealing surfaces, which can be cleaned.
(2) If the sealing surface is damaged, re-grind or re-surfacing and processing.