Product Introduction
A check valve refers to a type of valve whose opening and closing components are circular valve discs that act by their own weight and medium pressure to block medium backflow. It belongs to the category of automatic valves, also known as check valves, one-way valves, return valves or isolation valves. The valve disc movement can be divided into lifting and rotating types. Lift check valves have a similar structure to globe valves, except for the lack of a valve stem that drives the valve disc. The medium flows in from the inlet end (lower side) and flows out from the outlet end (upper side). When the inlet pressure exceeds the sum of the weight of the valve disc and its flow resistance, the valve is opened. On the contrary, when the medium flows back, the valve closes. A swing check valve has a valve disc that is inclined and can rotate around an axis, and its working principle is similar to that of a lift check valve. Check valves are commonly used as bottom valves in pumping devices to prevent water from flowing back. The combination of check valve and globe valve can achieve safety isolation.

Working principle
Check valves can also be used on pipelines to supply auxiliary systems where the pressure may rise above the system pressure. Check valves can be mainly divided into swing check valves (rotating according to the center of gravity) and lift check valves (moving along the axis). The function of check valves is to allow the medium to flow only in one direction and prevent the flow in the opposite direction. Usually, this type of valve works automatically, and under the pressure of fluid flowing in one direction, the valve disc opens; When the fluid flows in the opposite direction, the pressure of the fluid and the self weight of the valve disc act on the valve seat, thereby cutting off the flow. Check valves belong to this type of valve, which includes swing check valves and lift check valves. The swing check valve has a hinge mechanism and a valve disc like a door that freely rests on the inclined valve seat surface. In order to ensure that the valve disc can reach the appropriate position on the valve seat surface every time, the valve disc is designed in a hinge mechanism so that the valve disc has sufficient swing space and truly and fully contacts the valve seat. The valve disc can be made entirely of metal, or it can be embedded with leather, rubber, or a synthetic cover on top of the metal, depending on the performance requirements. When the swing check valve is fully open, the fluid pressure is almost unobstructed, so the pressure drop through the valve is relatively small. The valve disc of the lift check valve is located on the sealing surface of the valve seat on the valve body. Except for the valve disc, which can be freely raised and lowered, the rest of this valve is like a globe valve. Fluid pressure lifts the valve disc from the sealing surface of the valve seat, causing the medium to reflux and causing the valve disc to fall back onto the valve seat, cutting off the flow. According to the usage conditions, the valve disc can be made of all metal structure or embedded with rubber pads or rubber rings on the valve disc frame. Like globe valves, the passage of fluid through lift check valves is also narrow, so the pressure drop through lift check valves is greater than that through swing check valves, and the flow of swing check valves is less restricted.

installation
1、 Swing check valve: The valve disc of the swing check valve is disc-shaped and rotates around the axis of the valve seat channel. Due to the streamlined flow inside the valve channel, the flow resistance is smaller than that of the lift check valve, making it suitable for large diameter applications with low flow rate and constant flow changes. However, it is not suitable for pulsating flow and its sealing performance is inferior to that of the lift check valve. Swing check valves are divided into three types: single disc, double disc, and half disc. These three forms are mainly classified according to the valve diameter, in order to prevent the medium from stopping or flowing backwards and reduce hydraulic shock.
2、 Lift check valve: a check valve in which the valve disc slides along the vertical centerline of the valve body. Lift check valves can only be installed on horizontal pipelines, and ball shaped valve discs can be used on high-pressure small-diameter check valves. The valve body shape of the lift check valve is the same as that of the globe valve (which can be used interchangeably with globe valves), so its fluid resistance coefficient is relatively high. Its structure is similar to that of a globe valve, with the valve body and disc being the same as those of a globe valve and a silent check valve. The upper part of the valve disc and the lower part of the valve cover are processed with guide sleeves. The valve disc guide sleeve can freely rise and fall inside the valve disc guide sleeve. When the medium flows downstream, the valve disc opens by the thrust of the medium. When the medium stops flowing, the valve disc descends on the valve seat by self sagging, which prevents the medium from flowing back. The direction of the medium inlet and outlet channels of the straight through lift check valve is perpendicular to the direction of the valve seat channel; The vertical lift check valve has a medium inlet and outlet channel direction that is the same as the valve seat channel direction, and its flow resistance is smaller than that of the straight through type.
3、 Disc check valve: a check valve in which the valve disc rotates around the pin shaft inside the valve seat. The disc check valve has a simple structure and can only be installed on horizontal pipelines, resulting in poor sealing performance.
4、 Pipeline check valve: a valve in which the valve disc slides along the centerline of the valve body. Pipeline check valve is a newly emerged type of valve, which has a small volume, light weight, and good processing technology, and is one of the development directions of check valves. But the fluid resistance coefficient is slightly larger than that of a swing check valve.
5、 Compression type check valve: This type of valve is used as a boiler feedwater and steam shut-off valve, and it has the comprehensive function of a lift type check valve and a globe valve or angle valve. In addition, there are some check valves that are not suitable for pump outlet installation, such as bottom valves, spring valves, Y-shaped valves, etc.

precautions
1. Do not let check valves bear weight in the pipeline system. Large check valves should be independently supported to prevent them from being affected by the pressure generated by the pipeline system.
2. During installation, pay attention to the direction of medium flow, which should be consistent with the arrow direction marked on the valve body.
3. Lift type vertical flap check valves should be installed on vertical pipelines.
4. Lift type horizontal disc check valves should be installed on horizontal pipelines.