Selection and Installation of Common Check Valves

A check valve is a kind of automatic valve which relies on the weight of the fluid medium or external power to open and close the opening and closing parts (disc), and it is also called a one-way valve, which is widely used in petrochemical pipeline systems to prevent the medium from flowing back, avoid the drive motor from reversing and control discharge of the medium in the container. Correct and reasonable selection and pipe installation are directly related to the safe and stable operation of equipment and piping systems. Selection principles and installation requirements for common check valves are introduced in detail in this article based on the actual oilfield ground engineering project, and provide a certain reference for the majority of engineering designers by combining some examples of the installation of distribution pipes.
 
1. Selection of commonly used check valves
In oilfield ground engineering, commonly used check valves include lift check valves, swing check valves, butterfly check valves and diaphragm check valves. Different types of check valves have different disc structures as well as opening and closing methods, so their applicable working conditions are also different. Usually, in the early stage of engineering design, process designers select the type of check valve by qualitatively evaluating the required closing speed and speed characteristics of the check valve for minimum impact pressure or non-impact closing under specific working conditions. Although this method is not very accurate, it is generally suitable for most occasions.
 


On this basis, the selection of the check valve mainly follows the following principles:
(1) The nominal pressure of the check valve must match up with the production pressure required in the actual project.
(2) The check valve is not easily corroded by the fluid medium of the piping system.
(3) The friction loss of the check valve should meet requirements for process design when opening and closing parts are fully opened; ensure that the opening and closing parts are in the fully open state during normal production.

(4) The possible water hammer impact force of the check valve shall not exceed the strength of the equipment or piping system.

(5) The transverse strength and fatigue strength of check valve components should meet the requirements for production and operation.
(6) On the basis of meeting the design and production, the selected check valve should be economical, small in size, light in weight and suitable for transportation and maintenance.

(7) The applicable pipe sizes and pressure conditions of check valves with different structures are different, which has certain reference significance for the selection of check valves, as shown in the Table 1.

 
Table 1 Reference for the selection of specific check valves under different nominal diameters and pressure conditions

 
On the basis of the above valve selection requirements, predecessors have summarized some new types of check valves with good applicability for special working conditions. The designer can combine the actual engineering and fully consider the advantages of the new valve when selecting the model. For example, there are many high-efficiency silent check valves used in overseas oil and gas field ground engineering projects. The valve disc has light weights, quick operation, extremely short opening strokes (the fastest opening time is only 0.15s) and short structure length, which is especially suitable for long-distance transportation and can be installed at any position of the pipeline. There is no impact and noise when the valve is closed.
 
In addition, when the valve is closed under certain conditions, the water hammer impact force is required to be small or there should be no water hammer impact. It is recommended that  slow-closing swing check valves and slow-closing butterfly check valves should be used. However, in order to save investment, in the water supply pipeline with high pump head, short pressure pipe section and air pressure surge chambers, there is no need to use slow closing check valves. Ordinary check valves can ensure the safety of the project. On the contrary, for places with high pump head, long pressure pipe sections and no air pressure surge chambers, hydraulic control slow-closing check valves are selected at present. In the long-distance pipeline with low pump head, the medium backflow speed is slow, and the slow-closing check valves should not be used. The electric check valve should be selected to obtain the slow-closing effect.
 
As a piping professional designer, check valves should be installed reasonably according to process piping and instrument flow chart (P&ID). When a specific type of check valve is installed, it is necessary to fully consider its size parameters and installation conditions. In overseas oilfield ground engineering projects, parameters of check valves mainly refer to API, ASME, BS and other international general specifications, such as API 6D, API 594, API 602, ASMEB 16.34, BS 1868, BS 1873, ISO 15761, MSS SP-42, MSS SP-80, etc. In China’s oilfield ground engineering projects, they are mainly in accordance with GB/T12233, GB/T12235, GB/T12236, GB/T13932, JB/T8937 and other standards.
 
2. Installation points for attention for common check valves
The check valve should be installed in a place which is easy for operators to access and maintain. The internal structure of the check valve determines its unique installation characteristics. The following points need to be paid attention to:

(1) The check valve must be installed in strict accordance with the direction indicated by the arrow of the valve, and the reversed direction is not allowed.

(2) Straight-through lift check valves are often installed on horizontal pipelines, while vertical lift check valves can be installed on vertical pipelines where the medium flows from bottom to top.
(3) The lifting bottom valve is mainly installed on the standpipe at the end of the suction pipe of the water pump that cannot be self-primed or has no vacuum pump to pump air and water. The bottom valve needs to be submerged in water to prevent the water from flowing backwards, which enters the suction pipe or is poured into the pump and suction pipe in advance, ensuring that the water pump is normally turned on. There is a filter to stop impurities from entering the suction pipe and avoid damage to the pump and related equipment.
(4) The swing check valve is suitable for installing on horizontal pipelines; when it is installed on vertical pipelines, the medium must flow from the bottom to top, and it can also be installed on tilted pipelines.
(5) The wafer check valve is relatively flexible in installation positions, small in size and convenient for pipeline layout. It is often installed in a pipeline system with a DN between 100mm and 400mm to replace lift and swing check valves.
(6) The butterfly check valve has a simple structure and can only be installed on a horizontal pipeline; in order to reduce the installation height of a stop valve of a pump outlet, this type of valve can be considered as a priority.
(7) The slow closing check valve is installed for different ways. If it is placed in the well, there should be room for maintenance; it should not be placed in an environment below 0°C.
(8) The diaphragm check valve is generally installed between two flanges or tightened between pipe joints; the requirements for its working conditions are more stringent. For example, a corrugated ring rubber diaphragm check valve is more suitable for places with a wide range of medium flow changes, but the working conditions are limited to within 1MPa and 70°C.

(9) The check valve should be installed far away from the source of pulsation, and try to ensure that there is no major disturbance in the front and rear of pipelines. Some check valves have a requirement for the straight pipe length before and after them. Suitable supports and hangers can be chosen for pipeline layout to improve the stability of the pipeline, ensuring that the check valve is operated normally and its service life extends.