In the design of natural gas compressor stations, a check valve is a critical element which is commonly placed on the discharge side of the compressor to prevent reverse flow that can cause serious damage to the compressor itself and other components such as seals and bearings. One of the selection criteria of the check valve for this particular application is the valve flow characteristics in steady flow, and its dynamic characteristics in unsteady flow operation. With regards to steady flow valve characteristics, current models for the determination of the check valve open angle vs. mean flow velocity are based on semi-empirical data obtained from water tests, which were found to deviate from measurements in compressible flows. This paper presents results of steady compressible flow testing of an NPS 4 swing type check valve in air. Mean flow velocities vs. disc angles were measured together with several local pressure measurements at the back side of the valve disc. Comparison of these results with the EPRI model and Rahmeyer's model revealed that these two models underestimate the mean flow velocity for a given disc angle in compressible flows. A model was thus developed based on further refinement of Rahmeyer model but more suitable for compressible flows, and accounts for both torque contributions: i) from jet velocity impingement (K{sub}v) and, ii) from back the pressure distribution (K{sub}p). The work presented here points out to the need for better design of the disc shape particularly at the lower lip, and/or the valve body in order to create a lower disc back pressure to improve the disc lifting torque at lower mean flow velocity.
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