NEMO® PROGRESSING CAVITY PUMPS

# Geometrical Models of the Progressing Cavity Pumps

Find the right geometry for every application with the NETZSCH modular design

The NEMO^{®} progressing cavity pump belongs to the family of rotary positive-displacement pumps. The two conveying elements are comprised of the fixed stator and the rotor which turns within it.

Four different helical rotor and stator geometries, along with an extensive selection of sealing and material of construction options allow our specialists to select the NEMO^{®} pump that is tailor made for your application. The design is modular since the outer dimensions of the pumps are identical, as are the connections on the suction side and the discharge side, for all four geometries. With the exception of the rotor and the stator, all other components are also identical. This means that, if it is ever necessary to adapt a NEMO^{®} to new flow rates or pressures after installation, this can be done by simply exchanging the rotor and stator to better suit the new conditions.

### S/L Geometry

The helical eccentric screw/rotor has a circular cross section, a very long pitch and large thread depth. It oscillates in the fixed stator, which has an internal thread with the same profile as the rotor, but with 180° interval twin starts and twice the pitch. As a result of this half ratio lobe geometry, cavities are formed between the rotor and the stator when the two are put together. When the rotor turns within the stator, the progressing cavities between the two transport the medium in a smooth and continuous manner from the suction to the discharge side of the stator.

The flow rate is determined by the pitch of the rotor/stator, the diameter and the eccentricity, as well as by the pumping rotation speed. The pressure capability depends on the number of stages, with the differential pressure being up to 6 bar per stage. The two-stage NEMO^{®} pump in S-Geometry can reach differential pressures of up to twelve bar at a flow rate of 100 percent. A single-stage NEMO^{®} pump in L-Geometry has the same outer dimensions as the two-stage pump in S-Geometry, the same diameter and eccentricity, but twice the pitch of the rotor/stator. This pump therefore produces a flow rate of 200 percent over the S-Geometry at a differential pressure of up to six bar.

### D/P Geometry

The helical eccentric screw/rotor has an elliptical cross section, a long pitch and large thread depth. It turns in a circular eccentric motion within the fixed stator, which has an internal thread with the same profile as the rotor, but with 120 degree interval triple starts and 1.5 times the pitch. As a result of this two/three ratio lobe geometry, cavities are formed between the rotor and the stator when the two are put together. When the rotor turns within the stator, the progressing cavities between the two transport the medium in a smooth and continuous manner from the suction to the discharge side of the stator. The cavities in D/P-Geometries are about 75 percent of the size of those in S/L-Geometries, but they are passed through twice per revolution instead of only once, resulting in a flow rate 50 percent higher.

The flow rate is determined by the pitch of the rotor/stator, the elliptical diameter and the eccentricity, as well as by the pumping rotation speed. The pressure capability depends on the number of stages, with the differential pressure being up to six bar per stage. The two-stage NEMO^{®} pump in D-Geometry can reach differential pressures of up to twelfe bar at a flow rate of 150 percent over that of the S-Geometry. A single-stage NEMO^{®} pump in P-Geometry has the same outer dimensions as a two-stage pump in D-Geometry, the same ellipse and eccentricity, but twice the pitch of the rotor/stator. This pump therefore produces a flow rate of 300 percent over that of the S-Geometry at a differential pressure of up to six bar.