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Easy stirrup pump

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Unread postAuthor: saefroch » Sat Apr 09, 2011 9:37 am

Mark.f has a VERY good point. The brass housing for the check valve on my pump gets so hot I've burned myself on it before. :P You could very quickly melt hot glue and have a very serious problem on your hands.
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Unread postAuthor: LovableAirGuns » Sat Apr 09, 2011 7:04 pm

Ok because im not sure were they would sell low viscosity epoxy in Australia unless I use normal epoxy but that would be harder to use for filling the mould for a piston :/
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Unread postAuthor: Binary Blue » Mon Dec 31, 2012 1:38 am

Thanks for the instructions.

I would like to make something similar to your pump.

From what I've seen in other threads, would I be able to get higher pressure using smaller piping and components (1/2 inch)?

I would like to easily be able to reach 400 PSI. Can you pump reach 400 easily, or will it take some effort?

Here's my plan for a pump using 1/2 inch components.
Image

Will this work?

Also, will the check valves offered on McMaster Carr:
http://www.mcmaster.com/#standard-check-valves/=ktsfjn
be OK for use with pumps like yours?
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 31, 2012 6:25 am

The smaller the diameter, the higher the pressures you can reach, but the longer it will take you to reach them. I think 3/4" is a good compromise, especially if you don't need to go beyond 400 psi.

Beware the dead space in your check valve, any volume between the lowest position of the piston and the pump side of the check valve will affect your maximum pumping volume.

Simplifying the calculations a little:

Say you had a 0.75" dia pump with a stroke of 15".

With a dead space of say 1 cubic inch, you are going from 7.6 cubic inches to 1 cubic inch, meaning pressure is going from 15 psi to 114 psi and this is the highest pressure you can reach.

Reduce the dead space to 0.5 cubic inches and you can now go to 228 psi.

I suspect this is why Gippeto went through the trouble of making his own check valve.

A schrader can be adapted for this role with a bit of ingenuity.
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Unread postAuthor: Binary Blue » Mon Dec 31, 2012 7:18 pm

Thanks for the info JSR.

So can a pump similar to Gippeto's reach 400PSI easily and fill the reservoir and chamber in my design to that pressure?

My design is:

Image

It has a 6.09 in^3 reservoir with a 0.439 in^3 chamber.

Second, will the design even work?

Also, what formulas did you use to calculate the pump's properties (max pressure, pressure increase per stroke)?

EDIT: Will an inline check valve like this one:
http://www.ebay.com/itm/3-4-Stainless-S ... 35b93363c1

minimize dead space?

Here's the diagram the seller provided:
Image

Is this the correct direction of air flow:
Image
?
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 01, 2013 9:47 am

Binary Blue wrote:So can a pump similar to Gippeto's reach 400PSI easily and fill the reservoir and chamber in my design to that pressure?


yes

Second, will the design even work?


as drawn it should work well

Also, what formulas did you use to calculate the pump's properties (max pressure, pressure increase per stroke)?


It's a simplification based on Boyle's law:

http://en.wikipedia.org/wiki/Boyle's_law

if say you have a pump volume of 10 cubic inches, and a chamber volume of 20 cubic inches.

One stroke brings the pump volume to zero, meaning what was a total of 30 cubic inches is now 20 cubic inches.

This means that if we were starting from 15 psi atmospheric pressure, this now increases to 30/20 x 15 which gives us 22.5 psi, or roughly 7 psi increase per stroke. This of course ignores heat losses etc. but is a good approximation.

Is this the correct direction of air flow:
Image


Looks like it. That looks like a good design in terms of dead space. You can put some filler in the area denoted by diameter "B" in the diagram to reduce it further.
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Re: Easy stirrup pump

Unread postAuthor: air_dannon » Tue Apr 08, 2014 2:58 pm

Loving this pump I made from your plans, Gippeto. Couple questions: I initially added some moly grease to lubricate it and it worked great. As time and use go on it seems to be less lubricated and every so often, on the down-stroke, I can hear a slight release of air come up the shaft. How often should I re-moly the piston and do I need to try and remove/clean out the old moly? Also, are those short bursts of air release a concern? I'd hate to have 300psi steel handle come up at my jaw. :shock:
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Re: Easy stirrup pump

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Re: Easy stirrup pump

Unread postAuthor: Gippeto » Tue Apr 08, 2014 10:52 pm

Nice to see some folks still making use of this. :)

How often the pump will require lubrication is dependent upon how much you use it and what you lube it with. I suggest you take the simple route, and lube it when it seems needed. :wink:

If you can clean out the old lube without much trouble, that's likely a good idea.

The air leak you describe is not a real cause for concern, but does seem to be an indicator that maintenance is in order. An o-ring with a slightly larger od may also alleviate the issue.

Take care and have fun. :)
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Re: Easy stirrup pump

Unread postAuthor: jackssmirkingrevenge » Sun Apr 13, 2014 7:23 am

How about some sort of automatic oiler that dispenses a couple of drops with every stroke?
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