Features and Installation of Check Valves

A check valve is a valve that can keep the flow of fluid in a certain direction at all times, which has the function of preventing backflow. The valve disc will become opened under the action of fluid pressure, but if backflow occurs, the disc will closely attach to the valve seat under the action of back pressure to prevent backflow. A check valve has a feature of single way, which is suitable for clean media and is not good for media with solid particles and high viscosity. 
 
A check valve can be divided into a swing check valve, a lift check valve and a butterfly check valve. A structure whose one end of the disc-shaped valve clack is hung on the valve body in the form of a hinge for free movement is adopted, which has low pressure loss and easy fluid flow. A life check valve has a structure where the valve stem, hand wheel and other opening and closing operation parts are removed from the globe valve and the bonnet is added.
 
A butterfly check valve has a disc shaped like a disc, and it rotates around the shaft of the valve seats' passage. The butterfly check valve is divided into three types: the single disc type, double disc type and multi disc type. These three types are mainly classified according to the valve diameter; they are used to weaken the hydraulic impact when the medium stops flowing or flows backwards.
 
Installation of check valves
Example 1: In order to save installation space, designers sometimes directly connect adjacent valves and cancel straight pipe sections. Although such a compact layout can reduce costs and installation workload, in overseas oilfield ground engineering, valve selection and procurement should follow international standards. When foreign standard series such as ASMEB16.10 swing check valves are adopted, their structure and length are relatively small compared with China's standards. When flanged swing check valves with a DN bigger than 80 is directly connected, the bolt insertion distance is not enough. A straight pipe section must be added in the middle.
 
Example 2: Figure 1 shows the piping method of a steam pipe end for continuous use in a container. Figure 1(a) is wrong. The check valve should not be directly connected to the pipe mouth of containers. When the check valve is damaged, the container is connected to the outside world; if the medium leaks, it cannot be repaired. Therefore, a shutoff valve should be installed before the check valve, and it is recommended that a drain valve should be installed after a check valve. Figure 1(b) shows the correct design scheme.


Figure 1 The piping arrangement of the steam pipe mouth of containers