Another Dumb Question... :)

jeepkahn · Tue May 05, 2009 11:32 am

I'm thinking about making a stirrup pump , but I was going to use a piece of my 3/4" sch120 for the pump body... I'm only looking for 500ish psi, and the pipe is rated at 990psi(for water), and I plan on threading it mpt so that I can screw it into a 3/4" Tee that will house the homemade check valve, dead volume will be ALMOST non existent... 36" stroke x .69"diameter=13.45"3 / .0625"x.69" (dead space)=.023"3 for a compression ratio of about 585:1.... Any of you ME type folks wanna calculate where exactly in the stroke the pressures are gonna be upwards of 500psi so that I can figure out whether or not I'm gonna need to sleeve the lower coupla inches for burst strength... Considering the last .75" to 1" is going to be threaded into a brass fitting I don't think I'll have to, but I'd like to know either way........

Ragnarok · Tue May 05, 2009 12:11 pm

Well, in theory, pressures should get no higher than the opening pressure of your check valve + whatever pressure is on the other side. Well, I suppose that assumes unlimited flow, but it shouldn't rise too much above that.

However, assuming the pressures aren't high enough to open the valve, and calculating it as adiabatic compression... Last 2.84 inches will be at 500+ psi.

Of course, that's assuming you can actually exert the forces to get it compressed that far - but as it's only about 187 lbs, I guess that's probably not too beyond most people, even if some would have to jump around a bit on the end of the pump, or wear a heavy backpack...

jeepkahn · Tue May 05, 2009 12:27 pm

I actually weigh in at about 250lbs so 187lbs of force shouldn't be too hard, and I'm 6ft tall and would rather have a very long stroke rather than have to pump a gazillion times to reach high pressures...Hence the 3ft compression stroke....

On a side note... Santa just visited, and dropped off 10ft sections of copper pipe, type L in 1.5" and 1.25", and a 10ft piece of type k 1"....

this could get interesting...

Technician1002 · Tue May 05, 2009 6:18 pm

jeepkahn wrote:I'm thinking about making a stirrup pump , but I was going to use a piece of my 3/4" sch120 for the pump body... I'm only looking for 500ish psi, and the pipe is rated at 990psi(for water), and I plan on threading it mpt so that I can screw it into a 3/4" Tee that will house the homemade check valve, dead volume will be ALMOST non existent... 36" stroke x .69"diameter=13.45"3 / .0625"x.69" (dead space)=.023"3 for a compression ratio of about 585:1.... Any of you ME type folks wanna calculate where exactly in the stroke the pressures are gonna be upwards of 500psi so that I can figure out whether or not I'm gonna need to sleeve the lower coupla inches for burst strength... Considering the last .75" to 1" is going to be threaded into a brass fitting I don't think I'll have to, but I'd like to know either way........

Don't forget to do the math. The area of a circle is Pi times Radius Squared. 3/4 inch pipe has a radius of 1/2 that of the diameter of 3/4 inch. Area for that is just under 1/2 sq in so your pressure needed on the piston is in the neighborhood of just over 200 LBS.

You may want to consider a smaller bore for a 500 PSI pump.

When I use a hand pump, I like to keep some pressure on my feet so I'm not just standing on the pump handle.

Ragnarok · Tue May 05, 2009 6:41 pm

Technician1002 wrote:Don't forget to do the math.

I already did the maths. It's not quite a 3/4" bore, so the actual figure is the 187 lb figure I observed above.

If jeepkahn reportedly weighs 250 lbs, then it's a perfectly feasible option for him to use such a pump shaft diameter.

Of course, I wouldn't want the check valve to suddenly break, because you've suddenly got a pump handle flying at your face very fast. Ask Brian the Brain about that one.

jeepkahn · Tue May 05, 2009 7:27 pm

Rag already corrected you on the math, 3/4" sch120 is .69" as noted in my post (it's paintball barrel pvc, since you seem to show a high post count with apparently low post READING, I figured I'd clue you in)...

I have 36ft of the stuff because I had to get it special order...

The check valve should be relatively bomb proof..basically the t fitting will be the check valve... I'll do a quick sketch...

the yellow bit is .325" rubber disc...

inonickname · Tue May 05, 2009 8:18 pm

For a check valve you could use a schrader, but get one of the ones with an external spring so it can be modified. They should hold up just fine at these pressures - Gippeto even did a test on them.