SpudFiles

You have the correct formula and you are using it properly, but I think you used .75" for the id.?

Using .811" (3/4" type M) I get 252psi.

If you "leaned" into it on the downward stroke you might get very close to the 300psi you calculated.

Because everyone should have a copy;

http://www.copper.org/resources/pub_lis ... ndbook.pdf

In here, you will find dimensional specs, working pressure ratings, burst pressures, etc. It is very useful to have.

Gippeto wrote:You have the correct formula and you are using it properly, but I think you used .75" for the id.?

Yes I did...I was just using that figure to get a ballpark idea of the pressure I could generate.

very nice how-to \
I don't get why it doesn't suck vacuum
and according to the copper handbook a proper soldered 1" 50/50 tin lead can take 200 psi at a temprature of 100F

sniper hero wrote:very nice how-to \
I don't get why it doesn't suck vacuum
and according to the copper handbook a proper soldered 1" 50/50 tin lead can take 200 psi at a temprature of 100F

Thanks. I hope it encourages others to build something like it.

Can you expand on the "doesn't suck vacuum" bit?

You are correct in your interpretation of the charts in the copper handbook.

HOWEVER;

Lets take a quick look at good old 50/50 lead/tin and see what it's ACTUALLY good for, Hmm? (mind you, I still prefer 95/5 Tin/Antimony)

The shear strength of 50/50 is 36Mpa, that's 5221psi

The bonding area of a 3/4" type M joint is approximately 2.062 in2

That means that the maximum FORCE on the joint would be 2532 pounds(@ failure)


EDIT: I should NOT be doing (attempting?) math so far past my bedtime.

The correct answer is 10765.7 pounds of force @ failure. Obviously this will alter the rest of the calculations, so I'll re-do them too.

If we put that in terms of pressure, we get ~4213 psi

Edit: Nope, its 17942.83 psi (10765.7lb acting on .60in2)

This is the actual calculated failure point of our good old 50/50. As you can see, it's nowhere near the recommended max of 200 psi.

Edit: Still holds true.

Do I recommend you use 50/50 at anywhere near 17942.83psi?

HELL... NO

But am I going to get excited about this joint at 400psi ?

Not if I know it's properly soldered.

Edit:
A short treatise on brazing and joint lap/strength calculations;

http://www.thefabricator.com/TubePipeFa ... cfm?ID=575

ok thanx I think I get the not vacuum bit now
and about the pressure I feel better since the handbook van't be right always but still it is good to know wich pressure it fails because if it does it can be very dangerous.

no force=pressure*area

Do you care to expand on that thought somewhat?

gippeto
i see special hand pump on the internet that can pump up to 250 bar
and i can tell her piston area almost the same area for this pump you make
so what the mechanism in that high pressure air hand pumps
thank you

far_cry wrote:gippeto
i see special hand pump on the internet that can pump up to 250 bar
and i can tell her piston area almost the same area for this pump you make
so what the mechanism in that high pressure air hand pumps
thank you

They are 3-stage pumps like this one. http://www.google.com/patents?id=zPIQAAAAEBAJ

how the hell can i make something like this
at least i need cnc work place

Well, to make a 3 stage pump, you WILL need a lathe at the very least.

You could make a 2 stage pump without a lathe if your very creative.

Or, you could build this pump (or something similar) with a minimum of tooling.

That's why it is designed the way it is.

A simple 2 stage pump could be something like this.

thank you for respond
can you explane to me how it spouted to work i mean how the air flow. in the upper check valve or the lower and the flow way up or down. and where the high pressure air exit
and how much air pressure can i get from this 2 stage pump ?
don't angry i just love answers

I won't get angry. Answers are GOOD!


On the "up" stroke, the air in the "low pressure" cylinder (large diameter) is compressed into the "high pressure" cylinder. (small diameter)

On the "down" stroke, air is drawn into the "low pressure" (large cylinder). The air in the small diameter "high pressure" cylinder is compressed further and sent to your gun.

The rate at which the air is compressed in each stage will depend on the diameters chosen when building the pump.

Ultimately, the maximum pressure that could be generated will be dependant on the diameter of the small piston, the cracking pressure of the check valve, and the effort you can put into it.

I hope that helps. If not, I can try again.

i dont get it first time but wen i know thate small diameter piston have o rings close to the chech valve i know catch the idea
but why you dont have an check valve in the air inlet there are no vacum to suck the air into the larg cylinder

The air follows this path;

Down stroke;

The air enters the pump through the inlet in the side of the pump.

The air then flows through the check valve in the large diameter portion of the piston, into the chamber.


Up stroke;

The air is compressed in the low pressure cylinder, and forced down the center of the piston, past the second check valve, and into the high pressure cylinder.


Down stroke;

The air in the high pressure cylinder is further compressed and will no go through another check valve (not shown) on the foot of the pump, and on to your "device".

Repeat.