ISM0210 Instruction Manual of series SCE- Rev.03
Pag. 7/33
PUMP
DESCRIPTION AND OPERATING PRINCIPLE OF SIDE CHANNEL PUMPS
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Key feature of magnetic drive pumps is that the fluid that have to be moved never comes into
direct contact with engine parts, ensuring the physical separation between the motor and the
pump and the transmission is delivered via a coaxial magnetic coupling.
The pump consists of a part (outer rotor) that is coupled to an electric motor through elastic coupling (bare shaft
version) or directly (close couple) and a part (internal rotor integral with the pump impeller) that allows the
pumping fluid. The outer rotor is composed of a series of magnetic elements with features and size variations to
the torque to be transmitted. The inner and outer rotor magnets generate a magnetic field. At the start of the
electric motor the outer rotor rotating synchronously with the internal rotor, thus the power is transmitted to the
impeller pump, which acts as the pumping of liquid in the pump body itself. A static containment can, called rear
casing, located between the two rotors, separates the liquid from the atmosphere, making the pump seal.
The design of the side channel pump allows for the transfer of liquid-gas mixtures with up to 50% vapor;
therefore eliminating possible air or vapor locking that can occur in other pump designs.
This pump series is provided of a special centrifugal impeller that lowers NPSH requirement for the pump.
The side-channel pump design is similar to a regenerative turbine in that the impeller makes regenerative passes
through the liquid. However, side channel impeller design and casing as well as the principles of operation differ
greatly.
The side-channel pump has a channel only in the discharge stage casing (A) and a flat surface which is flush with
the impeller on the suction stage casing (B). A star-shaped impeller (C) is keyed to the shaft and is axially
balanced through equalization holes (C1)
in the hub of the impeller. The liquid or liquid/vapor mixture incomes
each stage of the pump through the inlet (B1). Once the pump is initially filled with liquid, the pump will provide
a siphoning effect at the inlet port similar to what happens in water ring pumps. The water remaining in the
pump casing forms a type of water ring with a free surface. A venturi effect is created by the rotation of the
impeller and the free surface of the water, thus pulling the liquid into the casing. After the liquid is pulled through
the inlet port, it is forced to the outer periphery of the impeller blade by centrifugal action.
It is through this centrifugal action that the liquid is accelerated and forced into the side channel. The liquid then
flows along the semicircular contour of the side channel from the outermost point to the innermost point until
once again it is accelerated by the impeller blade. The liquid moves several times between the impeller and the
side channel. Thus the rotating impeller makes several regenerative passes until the liquid reaches the outlet
port. The speed of the impeller along with the centrifugal action impart energy to the liquid through the
exchange of momentum, thus allowing the pump to build pressure.
The side channel leads directly to the outlet (A1). At the outlet port, the main channel ends and a smaller
minichannel (A2) begins. At the point where the mini-channel ends, there is a small secondary discharge port
(A3) level with the base of the impeller blades.
As the liquid is forced to the periphery through centrifugal action due to its density, the vapor within the liquid
stream tends to remain at the base of the impeller blades since it has a much lower density. The main portion of
liquid and possibly some vapor, depending on the mix, is discharged through the outlet port. A small portion of
the liquid flow follows the mini-channel and eventually is forced into the area between the impeller blades. The
remaining vapor which was not drawn through the outlet port resides at the
base of the impeller blades. At the end of the minichannel, as the liquid is forced into the area between the
blades, the area between and around the impeller blade is reduced.
The liquid between the blades displaces and thus compresses the remaining vapor at the base of the impeller
blades. The compressed vapor is then forced through the secondary discharge port where it combines with the
liquid discharged through the outlet port as it is pulled into the next stage or discharged from the pump. Thus
entrained vapor is moved through each stage of the pump.
Each subsequent stage operates under the same principle.
The number of stages can be varied to meet the required discharge head. When multiple stages are required, the
relative positions of the stage outlet ports are radially staggered to balance shaft loads.
