The term bypass means to circumvent or bridge. In centrifugal pump technology, it refers to a line that plays a key role in closed-loop control or as a balancing device. In the context of closed-loop control, it is possible to operate a centrifugal pump with a higher flow rate than that which is usable in the piping.
To this end, a bypass flow is branched off, which can either be routed back to the pump suction nozzle directly from the pump discharge nozzle through a narrow loop or reintegrated with the suction-side flow (after a delay) via different equipment such as a condenser and cooling unit.
When acting as a balancing device, the bypass is used to compensate axial thrust in boiler feed pumps.
Reasons to integrate a bypass:
- Operating behaviour: To stop further operation of the pump in the low-flow range
- Closed-loop control: for pumps whose pump input power curve slopes downward for high flow rates (e. g. propeller pumps, peripheral pumps)
- Thermodynamics: To prevent the fluid handled from heating up in the low-flow range. The bypass flow is branched off via an automatic recirculation valve (see
Valve) that is fitted to the discharge nozzle, usually of high-pressure and super-pressure pumps (e. g. boiler feed pumps).