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"0 Dead Volume" Pump Concept

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"0 Dead Volume" Pump Concept

Unread postAuthor: saefroch » Wed Sep 08, 2010 8:56 pm

So I was thinking about floor pump designs, using the floating o-ring pump head that we are all so familiar with, and I was wondering if I could actually get the dead volume on one down to 0. Well... I think I might have it.

My first thought is that the best way to get rid of all the dead volume, is of course to fill it with something. But... that's not so easy. What about hydraulic fluid of some sort?

Well if you just put some sort of liquid into a normal pump, the liquid will just be ejected past the check valve, but such a problem can be easily fixed by just flipping the whole pump upside-down. Now, you have no dead volume. For one pump stroke.

So, place a very weak spring on what was previously the pump head to hold it in the "pump" position, and force it to generate a slight vacuum before sliding into the "fill" position, and preventing any backflow of the hydraulic fluid out of the compressed volume.

Will this work? In theory? It seems pretty workable to me... but something tells me that with something this simple... somebody has already done it. I might try implementing this on my pump (as it's not quite finished yet and has room for additions). Suggestions and comments are very much welcome.

Oh, and I bet there's a patent on this already.

EDIT: Diagram:
Image

Brass colour is the pump structure, black is sealing material, red is a spring, blue is dead volume, to be filled by a liquid of some sort, and the grey is the pump head.
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Last edited by saefroch on Thu Sep 09, 2010 2:39 pm, edited 1 time in total.
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Unread postAuthor: Gun Freak » Wed Sep 08, 2010 9:01 pm

I think a rough sketch is in order here, but it sounds like a good idea.
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Unread postAuthor: Crna Legija » Wed Sep 08, 2010 9:05 pm

Your check valve will have to have some in order to move, you can get very little but not 0
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Unread postAuthor: Lockednloaded » Wed Sep 08, 2010 9:15 pm

I agree with -_-, but for a pump that has higher pressure you should make a multistage pump. IIRC, they are much more efficient and can reach much higher pressures
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Unread postAuthor: saefroch » Thu Sep 09, 2010 5:58 am

Multistages are also limited by dead volume, just the same a single-stage pumps. Considering my current chamber volume is just over 4 cubic inches... I don't know if a multi-stage is worth it. The idea of 0 or close to 0 dead volume is being able to reach 800 psi or so. I am looking into a multistage though... just a few engineering difficulties for me.

-_- wrote:Your check valve will have to have some in order to move, you can get very little but not 0

Explain?
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Unread postAuthor: Fnord » Thu Sep 09, 2010 12:25 pm

You could just use really thick grease instead of oil. Anything very maliable and compression resistant will work. You might even be able to use a flexible solid.
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Unread postAuthor: saefroch » Thu Sep 09, 2010 1:59 pm

It'd have to be very very malleable to fit into the tiny equalizer hole in the pump head and around the extra pump head to the o-ring. The only trouble with using a solid is I can't force air through a hole that's already filled with a solid.
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Unread postAuthor: Gippeto » Thu Sep 09, 2010 7:41 pm

800psi requires ~54:1 mechanical compression ratio...this should be rather easy to achieve with careful construction.

1/2" id pump tube will require 157 pounds force to achieve the 800psi.

With 20" of swept volume, the compression tube volume is ~3.93 in3.

If we make the assumption that the bottom 1/4" of the tube is ALL dead space (in reality, it'll be less than this) the dead space volume works out at .049in3

This leaves us with a mechanical compression ratio of 80:1 .... greatly exceeding the actual requirement to achieve the 800psi. Theoretically,we could get as high as 1176psi ...other variables not withstanding. :wink:
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Unread postAuthor: saefroch » Thu Sep 09, 2010 8:01 pm

And if you recall correctly, somebody has a 1,000 psi gauge, a brass check valve, and a 24" .495" ID 304L Stainless steel pipe in the basement. :wink: And I can already exert at least 170% of my weight in force on a pump. :wink:
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Unread postAuthor: Gippeto » Fri Sep 10, 2010 12:59 am

How...the...heck... do you know what I've got? :? :lol:

And it's in the closet in the spare room...not the basement. :P


What am I supposed to recall? Did I miss a post or something? :?
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Unread postAuthor: saefroch » Fri Sep 10, 2010 6:09 am

You MUST be kidding me... that list is stuff that's in MY basement... :? :lol:

I'm ordering a different configuration check valve soon, and some compression springs so I can get started working.
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Unread postAuthor: POLAND_SPUD » Fri Sep 10, 2010 9:48 am

@Gippetto & saefroch
How...the...heck... do you know what I've got? Confused Laughing

You MUST be kidding me... that list is stuff that's in MY basement... Confused Laughing

lol that reminded me this joke
One sunny day in Ireland, two men were sitting in a pub, drinking some Guinness, when one turns to the other and says "You see that man over there? He looks just like me! I think I'm gonna go over there and talk to him." So, he goes over to the man and taps him on the shoulder. "Excuse me sir," he starts, "but I noticed you look just like me!" The second man turns around and says "Yeah, I noticed the same thing, where you from?", "I'm from Dublin", second man stunned says, "Me too! What street do you live on?", "McCarthy street", second man replies, "Me too! What number is it?", the first man announces, "162", second man shocked says, "Me too! What are your parents names?", first man replies, "Connor and Shannon", second man awestruck says, "Mine too! This is unbelievable!"

So, they buy some more Guinness and they're talking some more when the bartenders change shifts. The new bartender comes in and goes up to the other bartender and asks "What's new today?" "Oh, the Murphy twins are drunk again."



:D
@seafroch
it's not a bad idea, but as Gippetto has pointed out you don't need fancy stuff to achieve 800 psi... and seriously, don't you think that it is a better idea to use a fridge compressor ?
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Unread postAuthor: saefroch » Fri Sep 10, 2010 2:52 pm

For a chamber volume of 5.7 cubic inches, with the predicted stroke volume at 4.1. Yeah. And I don't think I can find a fridgy that's battery-powered. My planned testing area for higher pressures is somewhat... remote.

The joke... is very apt. :lol:
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Unread postAuthor: Gippeto » Fri Sep 10, 2010 6:20 pm

saefroch wrote:The joke... is very apt. :lol:


You're a "drunken Irish twin" too? :shock: :lol:

Small world ain't it. :)

Uhh...wait a second...I'm not Irish, and I don't have a twin.

That only leaves..... :wink:
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Unread postAuthor: saefroch » Fri Sep 10, 2010 6:51 pm

:D Irish twins.
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