My impression is that piston pumps don't lose efficiency at lower RPMs
to the same degree turbine pumps do. This might imply that for given
performance requirements a physically larger, slower-rotating piston
pump might tend to have lower minimum required feed pressure without
impractically low efficiency. Maybe.
This opinion and two bucks will get you a cup of coffee...
On 12/15/2016 1:20 PM, Pierce Nichols wrote:
The piston cylinder volume still needs to be filled from tank pressure,
so there's a relation there between tank pressure and maximum pump
speed. IOW, it becomes another knob for the designer to twiddle.
-p
On Thu, Dec 15, 2016 at 12:03 PM, Brian Feeney <alaiadesign@xxxxxxxxx
<mailto:alaiadesign@xxxxxxxxx>> wrote:
Would a piston pump reduce or eliminate the problem of cavitation
one can get with a turbine? If yes, this would lead to lower tank
pressure, lighter weight tanks - buys back some of the weight
increase of the piston vs turbopump??
Cheers
Brian Feeney
On Dec 15, 2016 2:40 PM, "Henry Vanderbilt"
<hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
On 12/15/2016 9:15 AM, Dave McMillan wrote:
On 12/15/2016 11:01 AM, Thomas McNeill wrote:
I have been curious about different pumping mechanisms.
Instead of a
turbo pump what about positive displacement pumps, like
gear or lobe?
Has there been any attempt at using one of these types
of pumps?
I have to admit to being curious why I've never heard of any
amateurs trying a variant on XCOR's piston(less) pumps --
those seem
like a much lower bar to get over than any kind of
turbomachinery. Some
subtle difficulty I'm not seeing, there?
XCOR's pumps are not pistonless; that's Flometrics you're
thinking of.
As for the root question, I see no reason why developing an
electric-drive piston propellant pump should be particularly
challenging.
Off the top of my head...
- You need to pay attention to compatible piston-seal materials
(and to flow-path materials compatibility in general, of course).
- For cryos, you need to pay attention to thermal dimensional
issues, seal & lube temperatures, and flow-path conditioning.
- You need to pay attention to output pressure variations, to
the extent your motor/application may be sensitive to them.
None of those involve bleeding-edge new tech development. Just
a matter of known detail engineering. And there's this: There's
a HUGE existing parts-base out there for piston machinery
components, both in pumps for other applications
(pressure-washers anyone?) and in the small IC engine field.
I'd lean toward the explanation that people haven't looked at
piston over turbine pumps more out of established habit than for
fundamental practical reasons.
After all, if you're using a turbine for pump power, making the
pump a turbine wheel on the same shaft uses design/manufacturing
resources you'll need regardless.
Going to electric pump power, that no longer holds true. You
can now skip the (apparently) considerable investment in
high-performance turbine design/fab capabilities.
Henry
