View source for Progressing cavity pump

'''Progressing cavity pumps (PCPs) also Moineau pumps.''' <br>

Due to a quite astonishing and surprising geometric miracle despite …<br>
– the smooth non translatory motion and <br>
– the continuous non pulsing transport flow <br>
this is a positive displacement pump with closed chambers. <br>
As such it acts as a pump in the [[mechanical electrical analogy]] <br> 
more like a constant current source rather than a constant voltage source <br>
(given a non compressible liquid as medium). <br>

== Nanoscale peculiarities – biaxial curvature issue ==

While uniaxial bent structures are nicely possible by bending strain and systematic substitutions and such <br>
biaxial curvature (as in spheres and the complex curvatures of PCPs) is not so easily possibly. <br>
Advanced methods to design and [[mechanosynthesis|mechanosynthesize]] [[quasi amorphous structure]]s could help in getting <br>
inner walls of nanoscale atomically precise PCPs smooth to subatomic precision  <br>
thereby reducing friction and likely hood of backflow of smallest atoms and molecules like helium and hydrogen <br>

== Vacuum applications ==

Due to nanoscale atomically precise diamondois or more gemerally gemstone based <br>
structures being possibly such tight that even high pressure helium can't leak through gaps, <br>
these pumps will be usable to create very good (or even [[PPV]]) vacuum. <br>

Due to molecular flow having a hard time to find one small outled from a big chamber. <br>
One will want to cover walls with many nano PCPs <br>
walls similar to the size of the chambers pumped down. <br>

=== Advantage over trubomolecular pumps ===

Turbomolecular pumps need to operate near or above the speed of sound. <br>
Atomically precise sliding bearings would cause extreme friction heat at these very high speeds <br>
(see [[Nanoscale friction]]) so much so that they could not be operate steady-state in macroscopic quantities, <br>
some sort of active nanoscale electrostatic levitation bearing could still make them practically <br>
at a bit bigger scale. <br>
There's the possible issue of backflow through bearing gaps. <br>
Though ballistic molecular gas flow counteracts and <br>
clever geometries with interdigitating blades on the inside too likely can completely solve that <br>

Viscosity losses at near perfect vacuum are likely negligible. <br>
For pumping at higher pressures larrger scale PCPs may be <br>

Note that (while not totally obvious) there are two exactly equal 90° phase shifted reciprocative motions involved. <br>
Four PCPs need to be paired up to compensate by counter-motions and hugely reduce radiated vibrations. <br>
Higher multipole moment(?) <br>

=== Possible disadvantages of piston based positive displacement pumps ===

* More parts and more complex assembly 
* Possibly squeezed gas or liquid atoms (though the high thermals speeds compared to pump speeds might make that unlikely)
* Possibly more (complex) vibrations though PCP pumps feature two orthogonal 90° phase shifted reciprocative motions too. The wobbling.

== Ideas ==

=== Usage as motor with inherent-direct-geardown and self-cooling ===

The concept could be reversed and used as a motor.<br>
Wobbling the outer stator without rotating is around a fixed axis rotating inner rotor <br>
Using pulling actuators in three or more phases for the wobbling. <br>
The lobe number determines a decent gear-down ration. <br>
If a gas or liquid is present it can act acts as a coolant that is automatically pumped. <br>
Though this works better at larger scales due to falling viscosity issues. <br>
Low pressure hydrogen or helium might work for nanoscale - to analyze. <br>

== Related ==

* [[Quasi amorphous structure]]
* [[Reciprocation]] – reciprocation does not need to be translatory
* [[Reciprocative friction in gem-gum technology]]

== External links ==

* https://en.wikipedia.org/wiki/Progressing_cavity_pump 
* http://www2.mat.dtu.dk/people/J.Gravesen/MoineauPump/ ( nice page explaining the math - on internet archive too )
* http://www2.mat.dtu.dk/people/J.Gravesen/MoineauPump/HypoEpi4_3.html