The moineau pump is a positive displacement pump. The rotor and the stator are
the most important construction elements of this type of pump. The stator consists
of two spirals while the rotor has only one spiral. The rotor is constructed of steel.
The rotor then rotates around,
creating sealed spaces between the rotor and stator. Because of the spiral forms,
when the rotor rotated further, the new created spaces are moving axial from the
suction side towards the pressure side.
Because the suction side and the pressure side are always sealed of, the pump can
handle low viscous liquids. When the rotor rotates, a continues flow is being created.
The stator is vulcanized. This makes the stator very stable and decreases the wear out of the stator.
When the liquid has a higher viscosity or has a more abrasive character, the pump has to reduce it's speed. This means the capacity of the pump decreases when the liquid is more abrasive or viscous. When the liquid is aggressive or abrasive, it's advisable to keep the rpm from the rotor as low as possible, or use a larger type of pump.
The moineau pump can be divided into 3 traps.
Progressive Cavity Pumps
The progressive cavity pump is also known as the eccentric screw pump. The pump got this name, because it's a more suitable description of the functioning of the pump. Rene Moineau was the first to establish the principle of this type of operation.
The progressing cavity pump has one rotor rotating within a rubber stator. The rotor has the construction of a screw. The screw has double internal helixes. The pitch of the stator helix is twice that of the rotor's. The difference in pitch forms sealed cavities between the rotor and the stator which are caused to travel axially along the stator resulting in a smooth axial flow.
The progressing cavity pump has different methods of flexible couplings.
The simple single pin coupling
This type of coupling is suitable for small pumps with low torque requirements.
The open version of the single pin coupling
This coupling is used for small hygienic pumps. The coupling is used when the pump
needs to be cleaned internal thoroughly.
Hook joints
The most popular type of couplings are the hook joints. These couplings are suitable
for any pump size and can handle almost any application. The pin joints however, have
a drawback. The possibility of cyclic angular velocity changes. If a single hooke's joint
is used to transmit rotary power between two shafts which are not parallel, the driven shaft
will not rotate at a constant angular velocity. The speed isn't steady and changes continously
when the shaft is rotating. The cyclic angular velocity effects can be minimized by using
tow hooke's joints in series, at each end of the shaft. This approach is only effective when
the two joint angles are identical. It can not be guaranteed that the cyclic angular velocity
effects are eliminated. To guarantee this, there is another type of coupling available;
the constant velocity coupling
These couplings are constructed with a crowned gear, to mesh with a toothed annulus. The
angular motion is guided by a spherical bearing and the load is distrubeted over the
tooth flanks.
The progressing cavity pump is suitable for all kinds of liquids. From fluid to high-viscous liquids, abrasive liquids and are capable of handling liquids wich contains solid particles. The larger type progressing cavity pump can handle hard particles of 30 mm and soft particles up to 100 mm. The progressing cavity pump has a good suction capacity, but are sensitive of running dry.
The materials used for the pump casing and rotors vary from cast iron to titanium. The stator can be made of different forms of elastomer; natural rubber, nitrile rubber, Neoprene and Viton. The choice of the material depends on the chemical properties of the liquid, the nature of any solids and the temperature at which the pump will operate in.