Design and classification of centrifugal pumps
The centrifugal pump consists of the following main elements: volute casing, impeller inside the casing and sitting on the shaft. The impeller is inserted into the shaft by means of a key.
The shaft rotates in bearings, glands are arranged at the point where the shaft passes through the housing for sealing. Water enters the pump casing through the suction port and enters the central part of the rotating impeller. Under the action of the impeller blades the liquid begins to rotate and by centrifugal force is thrown from the center to the periphery of the impeller into the spiral part of the casing (in turbine pumps into the guide apparatus) and then through the discharge nozzle into the pressure pipe. As a result of the action of the impeller blades on the water particles, the kinetic energy of the engine is converted into pressure and velocity head of the jet.
The pump head is measured in meters of the pumped liquid column. The suction of the liquid is due to the vacuum in front of the impeller blades.
In order to create a greater head and better flow of liquid, the blades give a special convex shape, with the impeller rotating with the convex side of the blades in the direction of discharge.
The centrifugal pump must be equipped with the following fittings and devices: a receiving check valve with a grid1. Designed to hold in the casing and the suction pipe of the pump water at its inlet before starting; the grid is used to hold large suspensions floating in the water; a gate valve on the suction pipe, which is installed near the pump; vacuum gauge3 to measure the vacuum on the suction side. The vacuum gauge is installed on the pipeline between the gate valve and the pump casing; the crane for air discharge at the filling (installed in the upper part of the casing); the non-return valve on the pressure pipeline preventing water flow through the pump in the opposite direction at parallel operation of another pump; the gate valve on the pressure pipeline intended for start-up, stopping and regulation of productivity and pressure
Pump; pressure gauge on the pressure nozzle to measure the pressure developed by the pump; safety valve (not shown in the figure) on the pressure nozzle of the gate valve to protect the pump, pressure nozzle and pipeline from hydraulic shocks; a device for filling the pump.
In connection with the fact that pumping units are often included in the basic complex of equipment for regulation of operating modes of different purposes, they can be equipped with various automation devices.
Centrifugal pumps are classified by:
1) to the number of wheels [single-stage (single-wheeled), multistage (multi-wheeled)]; in addition, single-wheeled pumps with cantilever shaft arrangement - cantilever ones;
2) head [low head up to 2 kgf/cm2 (0.2 MN/m2), average head from 2 to 6 kgf/cm2 (0.2 to 0.6 MN/m2), high head more than 6 kgf/cm2 (0.6 MN/m2)];
3) method of water supply to the impeller [with one-way inlet of water to the impeller, with two-way inlet of water (double suction)];
4) shaft position (horizontal, vertical);
5) method of housing connector (with horizontal housing connector, with vertical housing connector);
6) method of fluid removal from the impeller into the spiral channel of the body (spiral and turbine). In spiral pumps, the liquid is discharged directly into the spiral channel; in turbine pumps, before getting into the spiral channel, the liquid passes through a special device - a guide device (fixed wheel with blades);
7) the degree of the speed of the impeller (slow, normal, fast);
8) type of pumped liquid (water supply, sewerage, acid and alkaline, oil, dredging, etc.);
9) method of connection with the motor [drive (with a gearbox or pulley), direct connection with the motor by means of couplings]. Pumps with pulley drive are rarely found nowadays.
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