DESMI SA

Operating principle, rapid and safe priming

The priming principle of the DESMI self-priming centrifugal pump is based on the diffuser principle. This means that the priming capacity is not dependent on valves or other mechanical elements since it is the liquid flow which carries the air. For priming, the pump casing is filled with liquid prior to starting. Due to the rotation of the impeller the liquid is immediately pumped from the suction chamber through the impeller into air separating chamber. Due to the negative pressure thus created in the impeller eye liquid is drawn through return passage, into the impeller. Due to the negative pressure in the pump, a check valve opens so as to draw air from the suction line into the pump where liquid and air are mixed and proceed through to the air separating chamber. The water velocity in the air purging space is so low that the air is separated from the liquid, and the vented water carries on the circuit through the return passage and the impeller until the total air content of the suction pipe has been separated.

Advantages

• Open impeller design Semi-open, non clogging high efficiency impeller allowing the pump to operate on dirty water.
• Replaceable wear plate To keep the pump at max. capacity even after working with abrasive fluids for a long time, the tolerance between impeller and wear plate may be adjusted by means of shims behind the replaceable wear plate.
• Mechanical shaft seal A reliable, spring-loaded, mechanical shaft seal ensures rapid suction, and shaft wear and stuffing box tightening are avoided.
• Check valve mounted at a high level The pump check valve is mounted well above the impeller inlet. Consequently, the pump will not - in case of a check valve leakage - lose the priming water which would result in a loss of priming ability.
• Heavy bearing design Heavy shaft and bearing design provide long life even in case of belt drive.