Paper on Turbopump Alternative

Peter Fairbrother wrote in message
One thing that might be done would be to introduce a very light piston, to
thermally seperate the drive gas from the pumped fuel/propellant. A disk of
foamed plastic, or the high-tech equivalent.

This idea is stated in the patent.

Quimby expanders are good for tolerance requirements, as the pressure
difference is split between several seals.

What is a Quimby expander?

Greg

tom perkins wrote

From what I can tell, the gas is doing work in going from 6000 to 600
psi. The only significant losses are seen in the
turbulence/shear/conversion to heat and noise occurring in the
expansion valve. Envision this:

A layer of gas is at 600 PSI in the filled pump chamber on top of the
propellant. The propellant is at the required pressure, but is not
moving to the engine. More gas at initially 6000psi is admitted to
the chamber, and this difference in pressure forces propellant to move
into the engine. The force exerted on the top of the propellant is
moved by the newly admitted gas through the distance required to
equilibrate the pressure of the newly admitted gas to 600psi, when
motion and expansion stop.

This motion is of course continuous, not intermittent, and the mean
pressure of the gas during an expulsion phase is above 600psi, enough
to overcome resistance losses and maintain a high flow rate.

Imagine this: the gas is first expanded from 6000 psi to 650 psi (without
doing any useful work) before it enters the cylinder. Would that make any
difference? No.

Or, if the gas was introduced all at once, so the initial pressure in the
cylinder was 6,000 psi and fell to 600 psi when the liquid was all expelled
- the liquid would be forced out at higher pressure (initially 6,000 psi,
falling to 600 psi), and the work done (= pv, pressure times volume) would
be greater.



--
Peter Fairbrother

Peter Fairbrother wrote in message
...


Quimby expanders are good for tolerance requirements, as the pressure
difference is split between several seals.

If the shafts aren't parallel then more work can be extracted as well.
Another way is to vary the depth, groove/land ratio, or the pitch.*


--
Peter Fairbrother


Where could I find info on Quimby expanders? Google coughed nothing up on them.

Thanks, TDP

Greg wrote

Peter Fairbrother wrote in message

Quimby expanders are good for tolerance requirements, as the pressure
difference is split between several seals.

What is a Quimby expander?

A screw pump has two shafts with opposite meshing threads in a close-fitting
container. The pockets created between the shafts and the container travel
lengthwise when the shafts rotate. Liquids or gases caught in the pockets
are thereby pumped.

The various pockets are at different pressures - say the first one is at
1500 psi, the second at 1,000 psi, the third at 500 psi and so on; as the
seals are between pockets they only have to contain 500 psi each, while the
overall pressure is 1500 psi.

A Quimby screw pump is a double screw pump, with screws at both ends and the
inlet in the middle. The screws are handed oppositely at each end so the
shafts have no overall endwise force, and the single stuffing box is on a
low pressure end.

There are a few other tricks than are used to increase performance, for
instance some have 3 shafts, but I'm not an expert.



These are all kind of hard to describe, but
http://www.animatedsoftware.com/pumpglos/quimbysc.htm shows a Quimby pump
suitable for liquids.


The Quimby expander is similar but the flow drives the shafts rather than
the other way round. If used for gases then the OD, depth and pitch of the
thread varies over the length of the screws.



--
Peter Fairbrother

Greg wrote

Peter Fairbrother wrote in message

Quimby expanders are good for tolerance requirements, as the pressure
difference is split between several seals.

What is a Quimby expander?

A screw pump has two shafts with opposite meshing threads in a close-fitting
container. The pockets created between the shafts and the container travel
lengthwise when the shafts rotate. Liquids or gases caught in the pockets
are thereby pumped.

The various pockets are at different pressures - say the first one is at
1500 psi, the second at 1,000 psi, the third at 500 psi and so on; as the
seals are between pockets they only have to contain 500 psi each, while the
overall pressure is 1500 psi.

A Quimby screw pump is a double screw pump, with screws at both ends and the
inlet in the middle. The screws are handed oppositely at each end so the
shafts have no overall endwise force, and the single stuffing box is on a
low pressure end.

There are a few other tricks that are used to increase performance, for
instance some have 3 shafts, but I'm not an expert. And no, I don't know how
the 3-shaft versions work! Anyone?



These are all kind of hard to describe, but
http://www.animatedsoftware.com/pumpglos/quimbysc.htm shows a Quimby pump
suitable for liquids.


The Quimby expander is similar but the flow drives the shafts rather than
the other way round. If used for gases then the OD, depth and pitch of the
thread can vary over the length of the screws.



--
Peter Fairbrother