Hi,
This is my first post here, so please excuse if its off topic.
I am building a model submarine capable of deep submerging, and to provide
its buoyancy control I need a pump capable of operating at a pressure of up
to 100 million Pascals, (= 1000 atmospheres, ~ 14,700 psi).
It has to push ~0.1 litres of a selected fluid (I get to choose this -
probably a non-compressible oil?) in under 15 min.
The power source is not a concern, but the design of such a pump is a little
tricky to my non-expert mind.
My inital idea was a simple piston, with a 1mm^2 bore area, running at 10
pumps per second, driven by a cog and hinged shaft, with a stroke length of
20 mm. ( A 1mm^2 area at 14700psi gives10Kg, or ~22 LBS weight force.).
Valves would control the flow direction.
The cog would be driven by worm drive, with possibly one gear reduction in
between.
Im trying to conserve energy, so need to minimise # of gears.
My concern with this is the compression stresses on the stroke shafts, and
the resulting frcture potential, and so I started wondering if a "pulling "
pump would be better, so as to put the shaft(s) in tension. Im thinking a
very high strrength steel, like lathing back a long 1.6mm dia. drill bit,
might be the simplest way to go, but a witha disimilar bore metal, I may
run into thermal expansion coeff probs....
Anyway, my questions are...
1. Is a piston pump, the best way to go, for simplicity, and practicality?
2. Is there any other pump designs (eg turbine, worm?) that could be a
better choice?
3. For a piston - type, is my initial idea roughly on the right track?
4. What kind of source metals should I use? ( I dont have a foundry or
anything fancy... so its hardware stores, and maybe some hobbyist lathes /
tools to get the job done).
Any comments would be appreciated.
TIA.
Dave Merrett,
Salisbury, South Australia.
This is way off-topic for u.r.m.r., but it does sound interesting! You
might be better off posting to a model boats newsgroup. Are you quite
sure about the pressures involved?
On 12/02/2006 08:23, Simone Merrett said,
Anyone who doesn't already know the answer to the question isn't
qualified to be around pressure vessels.
Just who is going to see your model at 30,000 feet, how will you
control it, and do you have enough mega money for trips to one of the
ocean trenches to run it? Somehow, something seems terribly wrong
here. Wrong newsgroups, wrong question, impractical concept.
IIRC, ultra-high pressure pumps are staged, anyway.
Without wishing to dampen your enthusiasm, to compress any fluid to
those pressures you will have to be sure of the purity and cleanliness
of them. Air at 6000 psig holds dangers of dieselling, so pressure
release has to be gentle and controlled. Newtonian fluids such as oil
and water do not compress but can flash off to gas - each having its
own unique temperature. The forces involved are going to be high and
I doubt if a reciprocator could be provided with crank bearings
sufficiently strong.
Regards
Peter A
Montarlot
France
Hi,
This is my first post here, so please excuse if its off topic.
I am building a model of a Trident submarine capable of firing off miniature
missiles while submerged, and to provide
its propulsion, I need a working nuclear reactor capable of fitting in a
submarine about one meter long.
The power source is not a concern, as I have access to a ready supply of
enriched uranium, but the design of such a reactor is a little
tricky to my non-expert mind.
My inital idea was a simple PWR, with an output of 32 gigawatts, etc
My concern with this is the compression stresses on the turbine shafts, and
the resulting frcture potential, and so I started wondering if an AGR would
be better, so as to put the shaft(s) in tension. Im thinking a
very high strrength steel, like lathing back a long 1.6mm dia. drill bit,
might be the simplest way to go, but a witha disimilar bore metal, I may
run into thermal expansion coeff probs....
Do you think if I make my own whitemetal bits and use traditional solder,
that will be any good for the reactor containment vessel?
Also, does anyone know whether Hornby still supply the Trident missiles with
working 2 megaton warheads from the "Thomas the Tank goes Nuclear on
Hogwarts" range, or will I have to make my own from brass etches?
Any comments would be appreciated.
TIA.
Steve,
Rampton,
England
You are going to have problems with flow past the piston. A bore of 20mm
and a stroke of 1mm would be easier ;-)
1000 atmospheres pressure is extremely dangerous and is way beyond you
if you're having to ask questions of us!
Think more in terms of one-three atmospheres pressure to be practical.
You may run into problems a 1-3 atmospheres pressure!
At the scale you're working in, a pump is probably the only workable way
to go.
No, clearances would reduce efficiency to nearly zero.
Think in terms of clearances in proportion to bore - you can't make a
1mm bore pump.
Consider the load on the big end bearings at the pressures you're
considering - that's a BIG bearing area! You might as well go for the
big bore/small stroke.
Consider the pressure on the "head" of the pump - you will need either
to make the head and bore in one piece or you're going to need some big
bolts!
At 14,700lb/sq.in most available metals will leak!
You can't connect the pump to anything - it will have to be part of a
fixed circuit built in solid metal!
Regards,
Greg.P.
Absolutely - I suggest that a suitable dry test spot would be any
underground railway station where any component failure would be
relatively confined.
Don't be daft, Greg. There is a London Transport bye-law specifically
forbidding spitting, smoking, drinking, or the conveyance of thermo-nuclear
assemblies or any other device likely to cause a public nuisance on any
Underground train.
Cheers,
Steve
Don't you be daft as well, Simon! If I was to use lead-free solder, then
we'd have radiation leaking out all over the place through the joints,
wouldn't we? And that would be the end of the W family line.
Let's just stay practical here.
Cheers,
Steve
I'm curious about something here. How exactly does this pump system
control buoyancy? It would seem that simply moving fluid from place to
place doesn't change the average density of the overall machine
much--if a small volume of water exterior to the hull is replaced by
this fluid, is that going to be enough? I'd have thought that a better
bet would be to have a cylinder filled with gas (maybe even air, but
there's probably some reason why a gas would work better) and then use
a piston worked from inside the hull to change its volume.
If the difference in mass of 0.1 litres of the fluid versus the same
amount of water would do the job, think how little volume change of the
gas would do the same. What would count here would be the specific
gravity of the fluid/gas (want something either much larger or much
smaller than 1--or some other figure if it's salt water, which
presumably it is since the depth is so great), and I'd have thought a
gas would be a better choice. Unless the fluid is mercury, maybe.
Oh hell, now I'm thinking of something even more stupid. Why not just
control buoyancy by extruding a solid bar through the wall of the hull?
A 0.1 litre volume change ought to be easy to achieve.
Or even warp the hull by jacking the sides apart. 100 ccs of volume
change, how hard could that be? Solve all your pressure-sealing
problems right there.
I have nasty feeling that you rotten pommy bastards are not taking
this question seriously and are mocking this chap - or is the
boot on the other foot or even hidden in his anarok?
"peter abraham" wrote
Hey, you're a pom yourself, living in France doesn't negate that! ;-)
If I wanted to find our about pressure pumps would I post to three model
railway groups - on each in the UK, USA and Australia or would I find a
group which was more appropriate?
John.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.