Pneumatic Cylinder For Bolt Action

[Jude]

Hello there,

Have too much question but lets start with;
Did anyone ever tried a pneumatic cylinder for a bolt action air tank..?
The idea is like the one in beeman p17 single stroke pistol but in a rifle with bolt action.
Do i have to use a qev with this too..? or should i think of a hammer valve system..?

[wyz2285]

There is too much dead space for it to be effective as a pump, specially a single stroke.

[Jude]

i guess 15psi (like 100kpa) for one shot may give 300-400fps to a 7.55gr .177 pellet so some calculations here gave me 3.2 kg of force on stroking the rod may compress and give 100kpa on the port for compressed air.

BTW not sure if 15psi for shot is enough for 300-400 fps, if you have any idea about that it would be nice too

[Gippeto]

15 psi not near enough. 125psi will not compress the skirt and start a pellet down the bore on it's own.Would think 200-300psi might be the minimum.

[Jude]

Thnx Gippeto

Now that compressing the skirts of pellets is an issue i may switch to bb's.
and now what i have to ask is, how can i replicate the air compression source in the beeman p17

[Gippeto]

Pump piston in a p17 is just a rod with an oring on it...dead simple. It's worked via a lever to provide mechanical advantage.

The tougher part is usually at the head of a pump, but being ssp, the p17 doesn't have a check valve. Just a small chamber and the exhaust valve.

Have one in the garage, will measure it up later and get back to you.

Edit;

Bore is .984"
Effective stroke length is ~3.9"
Mechanical advantage (class 2 lever) is 4

Will see if I can get an idea of valve volume tomorrow. If not, I'll close it on the bathroom scale and get an idea of the force required...can work backwards to get approximate developed pressure.

[Jude]

First of all i want to thank you for your interest, didn't thought someone to be involved at all. i have to say i am new to pneumatics and actually dont have an idea about how to replicate the single stroke system in p17.

I guess the small chamber at the end of the rod is where the compressed air is kept and the trigger is to switch the exhaust valve (thought it was a 2 position 3 way mechanical valve but guess it isn't or is it..?)

I wonder if you can make a list for me about what to find/buy for this project..?

[farcticox1]

I would start with a drawing/plan/layout.

[Jude]

I really don't know what type of parts to use and how to connect them into a pneumatic launcher so in this state I can't even draw anything about the design.

I actually hope to find answers here.
(BTW I can work with wood so after I know how the working pneumatics look like together, I will surely design and draw a good looking thing.)

[Gippeto]

Cannot run before you learn to walk.

Have a bicycle pump? Take it apart and learn how it works. Draw it out, follow the flow path of the air right through the pump. Think how changing one thing affects the rest of it...for example the bore, the stroke, the head space (volume at the end of the stroke)

Some basic formulas to help you with pumps...I don't know where you're at with schooling, you may already know some or all of this.

Pressure = force/area

So force on the pump piston divided by the area of the piston bore will equal the pressure.

Bore area * stroke length = cylinder volume

(Cylinder volume+ head space) / head space = mechanical compression ratio.


Mechanical compression ratio * atmospheric pressure = theoretical maximum achievable pressure. Can use 14.5psi for atmospheric pressure....it's close enough.

[Jude]

I actually know the formulas but we use metric system here in Turkey so it's a bit confusing each time calculating the imperial units.

For an example if i use a 1" bore and 4" stroke lenght my cylinder volume will be 3,14cu in and if i want to get 150psi from this cylinder its gonna be 150/3,14 = 47,77lb and thats like 22kg and too much for an arm to pump.

And so if i apply like 7lb to the piston with the same cylinder its gonna be only 22psi which is considered too low to launch a 0.2g bb or a 0.177 pellet

Here the head space you mentioned is the compression chamber in the pump i guess so if i use a head space half the size of the same cylinder volume (1,57) the mechanical compression ratio becomes 3 and the theoretical maximum achievable pressure is 43.5psi and that needs 13.5lb (maybe achieved with a lever) am i getting it right..?

btw i thought of the compression chamber as another unit outside the cylinder but when you said "head space" it may be in the cylinder too isn't it..?

[Gippeto]

Head space = compression chamber volume. Terminology is often where mis-understandings occur, but I think we're on the same page really.

Basically any remaining volume from the top of the piston on up as the total volume is being compressed into "that" space.

That 22kg with a 4:1 lever would only be a little over 5kg.

Have the P17 back together and will bring it in to test on the scale.

[Jude]

Now i have an idea about how to make the pump and the compression chamber its way easier than i thought but more questions are comming

I thought a qev should be between the compression chamber and the pump doesn't it..? (that way the system may also allow multi pump action)

For a simple start if i pass the qev on this one, what kind of valve should i use..? and how to attach it on the backend of the pump..?

(btw waiting your p17 test.. )

[farcticox1]

Is this what you are thinking ? this is actually quite interesting, might try a test sometime and see what sort of pressure I can get with cylinders /number of pumps etc.

Can somebody confirm if my circuit is correct, I did this VERY quickly.

[Jude]

Can't say if it's correct or not but the first idea I had was similar to this. Later on Gippeto said that the Beeman p17 is a simple cylinder and a rod pump with a chamber and valve at the end.

At first I'll try to make a prototype replication of the p17 with compression chamber within the pump and a 3/2 mechanic valve at the end would be enough I guess.