Tips for Selecting Check Valves

China valves are a kind of automatic valve that can open and close the disc by the weight of the medium or the exterior drive. In the oilfield surface projects, check valves commonly include lift, swing, butterfly, diaphragm and other types. Different kinds of check valves have different disc structures and open-close modes so that they can be applied to different working conditions. Generally, in the early stage of engineering design, professional designers select the types of check valves according to the qualitative evaluation of the closing speed and the speed characteristic required by check valves for the minimum impact pressure or non-impact closing under specific conditions. Although this method is not very accurate, it can be used for most occasions.

On this basis, the selection of check valves mainly adheres to the following principles:
1. The normal pressure of the check valve must be matched with the production pressure required in the actual project.
2. Check valves are not easily corroded by the media in the piping system.
3. When the disc is fully opened, the frictional losses need to meet the requirements of the process design. And the opening parts of the valves should be fully opened in the normal production.
4. The impact of the water hammer which may be generated by the check valve cannot exceed the threshold intensity of the equipment or piping system.
5. The flexural strength and the fatigue strength of components should satisfy the requirements of production and operation.
6. On the basis of meeting the needs, the check valve we choose needs to be economical, small in size and light in weight, which is suitable for transportation and maintenance.
7. Check valves with different structures are fit for different pipelines in various sizes and working conditions. The following table can be considered as a reference.

Some new type check valves with strong applicability have been summarized by people for special working conditions. According to the actual situation, designers can fully consider the advantages of these check valves. For example, the high-efficiency silent check valves have been commonly used in oil and gas field surface projects abroad at present. The disc of this type of valve is light and flexible with a small opening stroke (The fastest opening time is only 0.15s.) and a short structural length. It can be closed without any impact and noise. And this valve is suitable for long-distance pipelines and can be installed at any position of the pipeline.

In addition, under some special conditions, it is required that the impact of the water hammer is relatively small or there is no water hammer force when the valve is closed. So we can choose the slow-closing swing check valve and slow-closing butterfly check valve. However, to save investment, it’s all right to apply common check valves instead of slow-closing check valves to the water supply and delivery pipelines with high pump lift, short pressure pipe section and air surge tank to ensure the security of projects. On the contrary, hydraulic controlled slow-closing check valves can be used in the pipeline with high pump lift and long pressure pipe section and without an air surge tank. In the long-distance pipeline with low pump lift, the backflow velocity of the medium is slow, and we can choose electric check valves rather than slow-closing check valves to achieve the slow-closing effect.

As professional designers in piping, on the basis of optimizing the types of valves, check valves should be selected and installed reasonably according to the piping and instrument diagram (P&ID). When installing a specific type of check valve, take its dimension parameters and installation conditions into full consideration. In the overseas oilfield surface engineering projects, the parameters of check valves are mainly based on the international general specifications such as API, ASME, BS, including API 6D, API 594, API 602, ASME B16.34, BS 1868, BS 1873, ISO 15761, MSS SP-42, MSS SP-80, etc. And in domestic projects, we commonly refer to the standards like GB/T 12233, GB/T 12235, GB/T 12236, GB/T 13932 and GB/T 8937.