Most centrifugal pumps operate with a constant speed along a fixed curve. The pumps are integrated into plants with variable discharge flows. The variable flows lead to working areas where process related flowrates are below the required pump-specific minimum flow.
The pump minimum continuous flow (MCF) is the lowest permitted flowrate that the centrifugal pump can handle permanently without damage. The MCF is the lowest permitted flow that complies with the pump and plant’s requirements regarding a safe and economic operation.
To ensure the required flow rate does not fall below the permissible minimum, it is common to install a bypass with orifice between the pump’s discharge branch and the first shut-off device in the pressure line. The orifice device permanently allows the constant minimum flow to pass to the tank or to the suction line.
The orifice solution permits a constant loss of flowrate that considerably reduces the efficiency of the pump assembly. Based on economic and ecologic aspects, this solution is only acceptable for smaller low-pressure pumps with low minimum flows.
A good solution for large plants and high...
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