The NEMO Stator - netzschusa.com Geometries.pdf · The NEMO ® Stator The design and ......

© NETZSCH www.netzsch.com 07.08.2008 - 1

The NEMO®

Stator

The design and quality of a stator are critical to its performance and service life.

Therefore, NETZSCH keeps on developing new improved elastomers, and have established their own stator manufacturing facility.


• Each stator is manufactured individually and is fitted with

integrated seals (A) on both ends. Therefore, the stator tube

is hermetically encapsulated which prevents corrosion even if

aggressive chemical fluids are pumped. This design is also in

line with hygienic and aseptic requirements.

• Tapered inlet instead of flat entry

to reduce the NPSHr.

• Sealing by o-rings or gaskets (B) is

not a suitable technical solution.

The NEMO®

Stator

A

B


• Only precision tubes are used for the metal stator bodies.

Reason: higher dimensional accuracy and better bonding of

the elastomer.

• For every elastomer quality a specific core is used. This way

the various shrinkage rates during production are taken into

account. NEMO®

stators always have identical dimensions

regardless of what elastomers are used.

• For specific applications such as temperature changes in

food or chemical processes, stators with reduced elastomer

wall thickness are available.

The NEMO®

Stator


The NEMO®

Stator

Advantages:

high efficiency, low starting torque, stable pressure, low pulsation, long service life

A stator made from a cylindrical core will have unequal tolerances along its length. The compression at the ends of the stator will be too high, in the middle area it is too low.

Disadvantage:

higher starting and operating torque, low stability of pressure, higher pulsation, shorter service life.

interference too high insufficient interference

optimal interference

NETZSCH Standard

cylindrical core

The use of tapered cores produces a constant tolerance along the whole length of the stator


Interference

in the Rotor/Stator System

In order to achieve optimal efficiency and long service life, the interference between rotor and stator and the „d“/“D“ ratio of the interference are of vital importance.

Through continuous development NEMO® conveying elements have reached excellent mechanical and volumetric efficiencies, with low starting torque and minimum pulsation.

D

d


NEMO®

Rotor/Stator Geometries–Comparison For each application and each process the optimal solution

S-GeometryLobes: 1/2 Flow rate: 100% Differential pressure: 180 psi

D-GeometryLobes: 2/3 Flow rate: 150% Differential pressure: 180 psi

L-GeometryLobes: 1/2 Flow rate: 200% Differential pressure: 90 psi

P-GeometryLobes: 2/3 Flow rate: 300% Differential pressure: 90 psi


Comparison of Rotor/Stator

Geometries

n = const.

/ identical pumps with four different geometries

Q = capacity E = chamber/entrance cross sectionV = fluid velocity in conveying elementVgm

= average rubbing velocity of rotor surfaceMB

= operating torque at maximum working pressurePreq.

= power requirementFA = axial load on the end of the rotor

Geom. Q max. ∆p [bar] E V Vgm MB Preq. FA

2 S 1 12 1 1 1 1 1 21 L 2 6 1 2 1 1 1 12 D 1,5 12 0,75 2 1,1 1,5 1,5 2,41 P 3 6 0,75 4 1,1 1,5 1,5 1,2



GeometriesQ = const.

/ identical pumps with four different geometries

n = speed V = fluid velocity in conveying element

Vgm

= average rubbing velocity of rotor surface

MB

= operating torque at maximum working pressure

Preq.

= power requirement

FA

= axial load on the end of the rotor

Geom. n max. ∆p [bar] V Vgm MB Preq. FA

2 S 1 12 1 1 1 1 21 L 0,5 6 1 0,5 1 0,5 12 D 0,66 12 1,33 0,73 1,5 1 2,41 P 0,33 6 1,33 0,36 1,5 0,5 1,2



GeometriesQ = const.

(90 Gpm @ 60 Psi) different

pumps with four different geometries

n =

speed [rpm]V = fluid velocity in conveying element [m/s]Vgm

= average rubbing velocity of rotor surface [m/s]MB

= operating torque at maximum working pressure [Nm]Preq.

= power requirement [kW]FA = axial load on the end of the rotor [N]

Geom. Size n max. ∆p [bar] V Vgm MB Preq. FA

2 S 063 380 12 1,7 1,9 88 3,5 24801 L 045 580 6 3,5 1,85 60 3,6 12302 D 053 420 12 3,2 1,8 102 4,5 20101 P 038 520 6 6,4 1,85 64 3,5 1010


Advantages of D and P Geometry

• Identical dimensions but a 50 % increase in the flow per revolution compared to S and L geometry of the same size.

• A smaller pump size with specifically lower axial load generates a reduced rubbing velocity for the same flow rate.

• The increase of the number of cavities from two to three improves pumping capability and stability of pressure.

• Pulsation is clearly reduced (pls. refer to diagrams on the right) which is a decisive advantage in low pulsation dosing of e.g. coating colour via filter units on to a paper stream.

S and L geometry

D and P geometry


Advantages of NEMO®

S-Geometry

• very smooth conveyance

• compact dimensions despite high number of stages

• large cross section of rotor inlet

• low flow velocity/NPSH

• conveyance of compacted products is possible

• conveyance of large solids



L-Geometry

• good volumetric efficiency/long service life due to long seal line between rotor and stator

• compact dimensions together with high flow rates

• reduced rubbing velocity


Passage of media with L & S Geometry

cavities


Seal Line L + S -

Geometry

Reference Position


Seal Line D

+ P

-

Geometry

Reference Position



D-Geometry

• extremely compact dimensions despite high pressure and

flow rate capabilities

• almost pulsation free conveyance

• high dosing accuracy



P-Geometry

• compact dimensions in conjunction with very high flow rates

• almost pulsation free conveyance

• high dosing accuracy

• good volumetric efficiency/long service life due to long seal line

between rotor and stator

• reduced rubbing velocity


Passage of media with D & P Geometries

cavities

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