Air Cylinders
I’ve been contemplating having a go at making my own air rifle, the one thing that gives me pause is the air cylinder, we are dealing with a great deal of energy there.
I was thinking originally of using a talon bottle I have, but it does limit the designs somewhat.
but then I found that air-guns of Arizona is selling FX air cylinders 😀
you can get 148cc and 180cc air cylinders for what I think is a reasonable price, definitely worth the piece of mind.
they actually also sell the smaller extension so you really could get a pre-fabed air cylinder of the size you want 😯
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ohh ok….concrete example
MAC1 tubing….4130 alloy 7/8th OD 3/4 ID =1/8″ or .125″ wallthickness….yet he rates those tubes for 2500 ?
thats what i dont get when you then say .065 tube of i guess same material is fine for 3000 psi
note im not saying your wrong or anything…just trying to understand this
but still no answer why Mac1 say max 2500 psi on his .125″ wall tubes…
and DAQ says 2200 psi in a .065 tube….
which make me nervous of getting something that thinwalled, without somekind of explanation
Cygnus I answered yesterday but it got nuked in the transfer.
The thickness is but part of the equation. For a 1.25″ tube a 0.125 wall may be required. for a 1″ tube then 0.083″ and for a 7/8″ tube 0.065″ will all have the same 3,000psi design pressure.
Now depending on the fixing of the fill plug and valve that pressure may be further reduced depending on the method and location of the sealing.
Without actual tube specs with material and od,id it is impossible to compare pressures.
The MAWP is the 3,000psi in the example. Maximum Allowable Working Pressure. The test pressure is to assure the integrity of the vessel.
Arbitrarily increaseing the working pressure would require a redesign and then a new 150% test pressure.
It is a very poor practice to violate rated pressure esp when under cyclic loading like our air tanks and reservoirs.
There is no good reason for doing so therefore don’t.
Walter….
yes 89955K86 is what im looking for….
but still no answer why Mac1 say max 2500 psi on his .125″ wall tubes…
and DAQ says 2200 psi in a .065 tube….
which make me nervous of getting something that thinwalled, without somekind of explanation
I make my grooves only a 1/10 of a mm bigger than would theoratically be a 0 clearence. So When I need to seal a 24*2.5mm tube–>23mm id and I use a 1.5mm o-ring I make the groove 20.1mm. Never had any problems with sealing. An o-ring is not a gasket! It’s a little escaping pressure that eases the o-ring in the craves. I’d use a 0.05–>0.1mm clearence between valve body and tube id.
I know I use metric and it’s confusing with the rest using imperial but I hope I’ll have some good influence on the rest 😆
Btw daystate uses pinned valvebody. Although I think it’s a bit on the small size! Just 16mm pin holding back 1100kg. But I agree with tron. Proven and tested design!
Regards,
Marc
Okay, so if they test it to 4500psi then filling to say 3500psi is well within safe margins. Above that, even the 4500psi rating is quite a ways below what it would take for the tank to fail, although staying away from those upper limits is the order of the day.
Check part number 89955K86. Is that what you are looking for?
Cygnus X – Go down to “Raw materials” and look in the metals subsection. They have tube of many different dimensions in there. 🙂
cool thanks for the dimensions once again…(do remember them from last time i asked about it)
what makes me wonder though is that mac1 only rates his 4130 tubes at 2500 working pressure….and they are thicker walled than is suggestested by voltar….is he using some other material or is it the threads he takes into account ? ditto with DAQ who i think says 2200 psi for .065 walled….
doesnt mcmaster have some tubing that can be used…doesnt have to be black
for orings i have used tu cut as shallow groves as possible…the rubber will stretch and seal…just gotta make sure it cant squeese out
Homemade pinned cylinder on this page.
http://www.bryanandac.com/new_page_10.htm
Do a search for “Dooper” on that page. There are three pics of it.
Something that hasn’t been talked about. What type of Orings do you use for a config like that and how do you figure what depth groove they need? How much should they be compressed by the outer tube. Is there some rule of thumb with Orings?
When I do oring fits if the oring of choice is 0.070″ cross section I then make the oring groove diameter = bore id – 0.130″
So if using the 0.745 id of the 7/8″ tube the oring groove becomes
0.745 – 0.130″ = 0.615″ diameter.
If that fits seems on the tight side esp when sliding a valve into place i reduce the fit so that the installed oring measures in teh above case 0.755″ over the oring.
Never have any issues with leaks in any I have built doing it this way.
Cheers,
Walter….
As I recall this the design is say for a safety factor of 4 as to the strength of the material vs the operating stress.
Once the design is built it will then be tested to 1.5x the operating pressure to confirm the integrity of the complete system.
So in the above tubing design the tube is say 80,000psi tensile rated, the 4x safety allows 20,000psi stress and so from that we determine the operating pressure of 3,000psi.
Testing is then 150% of 3,000psi so 4500psi test pressure.
Make sense?
Walter….
Makes sense to me. I have also heard the 4:1 safety ratio in just about everything I have seen on the subject.
I’d like to see some videos of destructive testing on air cylinders. 😀
As I recall this the design is say for a safety factor of 4 as to the strength of the material vs the operating stress.
Once the design is built it will then be tested to 1.5x the operating pressure to confirm the integrity of the complete system.
So in the above tubing design the tube is say 80,000psi tensile rated, the 4x safety allows 20,000psi stress and so from that we determine the operating pressure of 3,000psi.
Testing is then 150% of 3,000psi so 4500psi test pressure.
Make sense?
Walter….
Just to clarify, if a Rifle is intended to be filled to say 3000psi from the Manufacturer, then what is the legal requirement for it to be tested to? I’m guessing the safety margin must be a lot.
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MAC1 tubing….4130 alloy 7/8th OD 3/4 ID =1/8″ or .125″ wallthickness….yet he rates those tubes for 2500 ?
thats what i dont get when you then say .065 tube of i guess same material is fine for 3000 psi
note im not saying your wrong or anything…just trying to understand this
For the record, .875″ od, .75″ id = .0625″ wall not .125. Just for funnies, keep in mind there are two walls. 🙂
Here is a link for burst pressures
http://www.rathgibson.com/technical_info/pressure_data/burst_pressure.aspx
For 4130N seamless tube, a fair number for yield would be 52KSI.
I’ll take a guess at the difference, it’s called liability.
Less is safer.