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A progressive cavity pump, also known as a progressing cavity pump, eccentric screw pump or even just cavity pump (also as is common in engineering generally, named after a major manufacturer; Nemo pump or ROBBINS & MYERS MOYNO PUMP), is a kind of pump that transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is turned. This leads to the volumetric flow rate being proportional to the rotation rate ( bidirectionally ) and to low levels of shearing being applied to the pumped fluid. Hence these pumps have application in fluid metering and pumping of viscous or shear sensitive materials. It should be noted that the cavities taper down toward their ends and overlap with their neighbours, so that, in general, no flow pulsing is caused by the arrival of cavities at the outlet, other than that caused by compression of the fluid or pump components. An electrically driven pump (electropump) for waterworks near the Hengsteysee, Germany. ...
A Siemens steam turbine with the case opened. ...
In fluid dynamics, the volumetric flow rate, also volume flow rate and rate of fluid flow, is the volume of fluid which passes through a given volume per unit time (for example gallons per minute or squeaks per parsec). ...
Shearing in continuum mechanics refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. ...
Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ...
The principle of this pumping technique is frequently misunderstood, often it is believed to occur due to a dynamic effect caused by drag, or friction against the moving teeth of the screw rotor. However in reality it is due to sealed cavities, like a gear pump, and so has similar operational characteristics, such as being able to pump at extremely low rates, even to high pressure, revealing the effect to be purely positive displacement (see pump). An exploded view of an external gear pump. ...
An electrically driven pump (electropump) for waterworks near the Hengsteysee, Germany. ...
Theory
The mechanical layout that causes the cavities to, uniquely, be of fixed dimensions as they move through the pump, is hard to visualize (its essentially 3D nature renders diagrams quite ineffective for explanation), but it is accomplished by the preservation in shape of the gap formed between a helical shaft and a two start, twice the wavelength and double the diameter, helical hole, as the shaft is "rolled" around the inside surface of the hole. The motion of the rotor being the same as the smaller gears of a planetary gears system. This form of motion gives rise to the curves called Hypocycloids. Epicyclic gearing is used here to increase output speed. ...
In geometry, a hypocycloid is a special plane curve, a roulette, generated by the trace of a fixed point on a small circle that rolls within a larger circle. ...
In order to produce a seal between cavities, the rotor requires a circular cross-section, and the stator an oval one. The rotor so takes a form similar to a corkscrew, and this, combined with the off-center rotary motion, leads to the name; eccentric screw pump. A basic corkscrew A corkscrew is a tool for drawing stopping corks from wine bottles. ...
Different rotor shapes and rotor/stator pitch ratios exist, but are specialized in that they don't generally allow complete sealing, so reducing static pressures and flow rate linearity, but improving actual flow rates, for a given pump size, and/or solids handling ability.
At a high enough pressure the sliding seals between cavities will leak some fluid rather than pumping it, so when pumping against high pressures a longer pump with more cavities is more effective, since each seal has only to deal with the pressure difference between adjacent cavities. Pumps with between two and a dozen or so cavities exist.
Operation In operation progressive cavity pumps are fundamentally fixed flow rate pumps, like gear pumps and peristaltic pumps, and this type of pump needs a fundamentally different understanding to the types of pumps people are more commonly first introduced too, namely ones that can be thought of as generating a pressure. This can lead to the mistaken assumption that all pumps can have their flow rates adjusted by using a valve attached to their outlet, but with this type of pump this assumption is a problem, since such a valve will have practically no effect on the flow rate and completely closing it will involve very high, probably damaging, pressures being generated. In order to prevent this pumps are often fitted with cut-off pressure switches, burst disks (deliberately weak and easily replaced points), or a throttleable bypass pipe that allows a variable amount a fluid to return to the inlet. With a bypass fitted, a fixed flow rate pump is effectively converted to a fixed pressure one. An exploded view of an external gear pump. ...
Linear peristaltic pump Linear peristaltic pump A peristaltic pump is a type of positive displacement pump used for pumping a variety of fluids. ...
These water valves are regulated by handles. ...
While progressive cavity pumps offer long life and reliable service transporting thick or lumpy fluids, abrasive fluids will significantly shorten the life of the stator. However slurries (particulates in a medium) can be pumped reliably as long as the medium is viscous enough to maintain a lubrication layer around the particles and so provide protection to the stator.
Typical design Specific designs involve the rotor of the pump being made of a steel, coated in a smooth hard surface, normally chromium, with the body ( the stator) made of a molded elastomer inside a metal tube body. The Elastomer core of the stator forms the required complex cavities. The rotor is held against the inside surface of the stator by angled link arms, bearings (which have to be within the fluid) allowing it to roll around the inner surface (un-driven). Elastomer is used for the stator to simplify the creation of the complex internal shape, created by means of casting, and also improves the quality and longevity of the seals by progressively swelling due to absorption of water and/or other common constituents of pumped fluids. Elastomer/pumped fluid compatibility will thus need to be taken into account. The interface between rotor and stator has to be lubricated by the fluid being pumped (Hydrodynamic lubrication) so can require extra torque to start, and if allowed to operate without fluid, called 'run dry', then rapid deterioration of the stator can result. General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Standard atomic weight 51. ...
Casting may be used to create artistic sculptures Casting is a manufacturing process by which a molten material such as metal or plastic is introduced into a mold, allowed to solidify within the mold, and then ejected or broken out to make a fabricated part. ...
Hydrodynamic lubrication has four essential elements: Lubricant medium, in this case, liquid water. ...
Torque applied via an adjustable end wrench Relationship between force, torque, and momentum vectors in a rotating system In physics, torque (or often called a moment) can informally be thought of as rotational force or angular force which causes a change in rotational motion. ...
Two common designs of stator are the "Equal-walled" and the "Unequal walled". The latter, having greater rubber wall thickness at the peaks allows larger-sized solids to pass through because of its increased ability to distort under pressure.
Typical application areas - Food pumps
- Viscous chemical pumps
- Small sewage pumps
- Sewage sludge pumps
- Slurry pumping
- Heavy oil pumping
- Cement pumps
SLUDGE (Scripting Language for Unhindered Development of a Gaming Environment) is a shareware adventure game engine developed by Hungry Software. ...
Specific uses - Clay slurry pumping
- Carbonate slurry pumping
- Mud motors
- Marine Diesel fuel pumps
The progressive cavity pump is used in reverse as a motor when drilling directional oil wells see directional drilling. ...
External images
External links detailed pump development description COMPENSATING ECCENTRIC MOTION IN PROGRESSING CAVITY PUMPS
Alternative description glossary of pumps
Alternative description Graco Inc (bottom of page)
Magazine entry/description for a Pump from Netzsch, Eureka magazine article
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