| Abstract: | Recent numerical investigations on pressure surges during pump trip in pumping installations showed that by including an air entrainment variable wave speed model, reasonable predictions of transient pressure surges with proper phasing and attenuation of pressure peaks can be obtained. These calculated results are consistent with similar field measurements made with the pumps operating at low pump cut-out levels, when air entrainment due to an attached surface vortex was observed. However, in the numerical calculation procedures it is assumed that the inertia of the moving elements of the check valve is small and that the check valve closes at zero reverse flow velocity. In practice, check valves seldom close precisely at zero reverse flow velocity. With the check valves not closing at zero reverse velocity, the present numerical computations show that the air content in a fluid system can adversely affect the check valve performance. With the fluid system operating within a critical range of air entrainment values, the present analysis showed that there is a possibility of ‘check valve slamming’ when the check valves are selected based only on the analysis of an air-free system. This phenomenon is confirmed through field observations. |
