Selection criteria for check valves
In oil field surface engineering, commonly used check valves include lifting type, swing type, butterfly type, diaphragm type and other types. Different types of check valves have different disc structure and opening and closing mode, so they are applicable to different working conditions.Usually, at the beginning of the engineering design, the process professional designer selects the type of check valve according to the qualitative evaluation of the closing speed and velocity characteristics required for the check valve to close with minimum impact pressure or without impact under specific working conditions.This method is not very precise, but it is generally suitable for most situations.
On this basis, check valve selection standards mainly follow the following principles.
(1) The nominal pressure of the check valve must match the production pressure required in the actual project;
(2) Check valves are not easy to be corroded by the fluid medium of the pipeline system to which they belong;
(3) The friction loss of check valve opening and closing parts must meet the requirements of process design, and the opening and closing parts must be fully open during normal production;
(4) The water hammer impact force that may be produced by the check valve shall not exceed the threshold strength of the equipment or pipeline system;
(5) The flexure strength and fatigue strength of check valve assembly shall meet the requirements of production operation;
(6) On the basis of meeting the requirements of design and production, the check valve should be economical, small in size, light in weight, suitable for transportation and maintenance;
(7) The applicable pipe sizes and pressure conditions of check valves of different structures are different, which have certain reference significance for the selection of check valves.
On the basis of the above valve selection requirements, predecessors have summarized some new check valves with strong applicability for special conditions.Designers can be combined with engineering practice, fully consider the advantages of the new type of valve selection.For example, the efficient silent check valve is widely used in overseas oil and gas field surface engineering projects. The disc has light weight, sensitive action, very short opening stroke (the fastest opening time is only 0.15s) and short structure length. It is especially suitable for long transmission pipeline and can be installed in any position of pipeline without impact or noise when it is closed.
In addition, under some specific working conditions when the valve is closed, water hammer impact force is small or no water hammer impact, it is recommended to choose slow closing swing check valve and slow closing butterfly check valve.However, in order to save investment, there is no need to use slow closed check valve in the water supply pipeline with high pump head, short pressure pipe section and pneumatic regulating chamber. The common check valve can ensure the safety of the project.On the contrary, in the case of high pump head, long pressure pipe section and no pneumatic mediation room, the liquid controlled slow closed check valve is mostly used at present.In the long transmission line with low pump head, medium backflow speed is slow, and slow closed check valve should not be used. Electric check valve should be selected to slow close the effect.