Pressure Cylinders or Vessels

Yep the prices are scrary arnt they …hehe . By the time youve done the machining and messing is it realy worth it!. Which is why its cheaper to buy a cylinder for another gun . You can buy a S200 cylinder for £50 new ,think im going to advertise for a secondhand cylinder on the UK forums , worked for Baz , and se what im offered 😀

Well as some of you may have spotted in my first post i work in the hydraulics industry for a company that designs and builds mainly hydraulic rams.
After talking to the guys in the drawing office about pressure vessel design it became quite clear to me that it is quite a complex subject involving quite a lot of calculations.
One of the lads emailed me a programme which i then emailed to myself at home,only to find i’m unable to open the programme due to it being on microsoft exel 😡
The beauty of the programme is you put in all your info such as tube material yield strength ,thread length ,pressure,thread root dia plus a couple of other pieces of info which you get from a engineers handbook and it works out the safety factor for you.
I,m unable to use this programme but im more than willing to email it to anyone who can use it.
BLACKOPS
You hit the nail on the head with your picture of the threaded end this is exactly how we seal our rams,although what we tend to do is bore the threads out to a bigger than bore internal diameter and put a 30 degree chamfer from the thread diameter down to the bore diameter this allows your o-ring to ride up the chamfer and into your main seal diameter without damage.
A lot of the time we use something called a back-up ring at the outer side of the o-ring,this is a solid plastic ring the same diameter as the o-ring designed to stop the o-ring extruding down the small gap left between tube and gland.
You can also use 90 shore o-rings instead of the more common 70 shore o-ring this also helps against extrusion.
We use tube from a firm called voss
Voss UK LTD
Tyson Courtyard
Corby
Northamptonshire
NN16 8AZ
Tel 01536 401012
Im not too sure if they will supply short lengths but well worth a try,here is a table of tube and pressures that they supply
OD x Wall Thickness Weight Kg/M Working Pressure Burst Press

20X2.5 1.08 311 1220
20×3 1.26 373 1450
22×2 0.986 226 820
25×2 1.13 199 670
25×3 1.63 298 1050
25×4 2.07 398 1520
28×2 1.28 177 620
28×3 1.85 266 920
30×3 2.00 248 920
30×4 2.57 331 1250
35×2 1.53 142 470
35×3 2.37 213 720
35×4 3.06 284 1280
38×4 3.35 261 970
38×5 4.07 327 1350
42×3 2.89 177 580

All the pressure figures are in Bar
Hope this little bit of info helps you, i will try and get some figures together and show how to calculate end plug thread strengths.
Nobody seemed too keen on drilling through the side of the tube and pinning and all agreed threading the tube internal bore far stronger with far less chance of failure as long as the threads are a good fit with one another.
Yours Mark
Forgot to add if anyone is struggling for tube give me a shout and i will try and help

i would go with the plug and screws from the side…easiest to do right….mac1 started with 4 screws in his bigtube ft rifle, but the aluminum walls stretched the holes in the tube…so i belive he ended up with 6 screws holding it in place…but he is also using a giant tube with a huge ID which puts alot of stress on the endcap (he uses steam80 pipe or so he said in a mail to me)

tapping the tube, is whats done on the b5x…DAQ has some exelent writeups about that on his website….

if i had the tools and machinery i would thread the tube…but for us guys that just tinker with the stuff its alot easier to just to the plug instead

i would go with a moly tube….the weight saving in using aluminum is next to nothing, as you would need alot more aluminum to accomplish the same thing, that a thinner walled moly tube will do….endplugs can still be aluminium(as it is in the b51)

Here’s a calculator:

http://www.engineersedge.com/calculators/shell_internal_pres_pop.htm

…and if you haven’t seen this yet, check it out (down the page, where
he talks about pressure tubes):

http://quackenbushairguns.com/steel_for_airguns.htm

William

work up dimensions based on say 15,000 tensile for ally and 20,000 for ChromeMoly. Shouls be able to sort out wha tyou need from that as to wall thickness. Make decisions of fastening method based on minimum wall allowed in the design.
I prefer the screwed system as it is easy to manage on a mill with dividing head. large lathe is used to prep tube ends and after that it becomes mill work. And possible in a drill press with suitable jigs and fixtures.
Walter….