The Centrifugal Pump
Overview
End-suction and self-priming centrifugal pumps (liquid ring pumps) constitute the core of the products manufactured and supplied by HILGE.
In general, these pumps are designed to cope with media featuring diverse physical and chemical characteristics. Their use is due to the fact that media can be most economically moved in pipelines. For this purpose a permanently installed pump is built into the respective pipeline at the starting point. The pump applies the necessary force to the media by sucking it in on one end, and discharging it on the other. This causes a pressure increase on the discharge side of the pump (at the pressure connection) and a reduction in pressure at the suction side of the pump (suction connection).
The centrifugal pump supplies the energy required via an impeller fitted with vanes. As a result of the effect of the vanes on the media, pressure and velocity are increased. To translate the increase in velocity into an increase in pressure, the media coming out of the impeller is channelled into an expanded ring space (channel). As the height required increases you reach a limit beyond which, for a defined flow, it is no longer purposeful to use a single impeller. You may be able to calculate velocity and the appropriate impeller for any height, but you run the risk of poor efficiencies and complicated designs. On the other hand, it is sensible to overcome any height of the discharge head by adding several impellers in series, i.e. to use a multi-stage centrifugal pump.
Due to their design, centrifugal pumps cannot vent the suction line when started up, meaning that they cannot initially draw up the media themselves. You must either arrange suction pipework so that the fluid falls under gravity from a vessel above the pump or fill the pump and the suction line with fluid before starting it. In addition, centrifugal pumps are even more sensitive to air pockets or bubbles in the media, which can lead to a breakdown if air pockets collect in the impeller channels. Self-priming centrifugal pumps such as liquid ring pumps are capable of venting the suction line. This requires the pump to be at least half-full of fluid. The star-shaped impeller thrusts the fluid in the pump into the side channel. This creates a suction on the suction side of the pump which is then capable of venting the suction pipework. The atmospheric pressure on the fluid surface then forces the fluid up the pipework to the pump. Bypass pumps can draw from depths up to 6m, depending on the physical properties of the media (steam pressure, temperature).
