Piston Qn.

[jackssmirkingrevenge]

Hmmmm makes sense but I still that a bit of extra travel would be beneficial....

Why?

or rather, por que?

Beyond the magical caliber/4 figure, you are getting absolutely no extra advantage in flow - simply increasing pilot volume, and also expanding the size of the air reservoir which in turn lowers the pressure.

[Gepard]

'Cos it saves the gas going right around and then in,
Chances are you can't get exactly d/4 and so it's best to err on the side of performance.

Only talking about an extra 5-10mm not lots....

Michael

[jackssmirkingrevenge]

'Cos it saves the gas going right around and then in

Sorry for being such an efficiency nazi but I can't stand waste. In practical terms, a few mm won't make *that* much of a difference, but since air is a limited power source compared to solid propellants, it makes sense (for me at least) to want to extract every available ft/lb from a specific launcher.

No matter how much the piston moves back the air in a coaxial is still going to have to change direction to exit through the barrel, I don't see how it will improve performance to have the piston move back further.

[Gepard]

We talking about a co-axial? I thought we were talking about piston valves in general......

Michael

[Modderxtrordanare]

We talking about a co-axial? I thought we were talking about piston valves in general......

Michael

Does it matter? The air still has to turn around 180°.

[Gepard]

I don't see the need to carry on this thread....

Where does it go round 180 degrees in a 'normal' piston?

Michael

[Modderxtrordanare]

I don't see the need to carry on this thread....

Where does it go round 180 degrees in a 'normal' piston?

Michael

If you have an over under set up like the majority of the barrel sealing piston valves that have been made, the air goes through two 90° bends. It's not an immediate 180° turn. But some of the air, such as in the pilot area outside of the barrel, does have to make a 180.

Edit: I just noticed Jack's avatar being animated, maybe I'm just retarded though...

[Gepard]

Ah - true, but I was refering to the flow of the gas from the chamber to the barrel through the piston.

Michael

[dongfang]

Hi jack.....

for 1/4 of the caliber of travel, you get an available area of 2*pi*r*h, in this case 2*3.142*0.5*0.25, which equals 0.7855 in 2

You have a hangover all right.

What's pi doing in the formula for the area of a rectangle? Your valve passage is really pi times smaller than the barrel cross section.

Gepard:

Where does the 90 come into it?

I must ask you that? You were the one who started with a 90 somewhere

I guess it is our valve seat diameter.

Regards
Soren

[Gepard]

No - he's right, he's talking about a co-axial where gap the piston leave is a cylinder.

You mentioned 90 in your post. I even quoted you!

Michael

[dongfang]

Ok, coaxial. Maybe I should read what they write

Hey, that is sure in favor of the coaxial in efficiency.

Soren

[jackssmirkingrevenge]

You have a hangover all right.

What's pi doing in the formula for the area of a rectangle? Your valve passage is really pi times smaller than the barrel cross section.

I'm the one who should be asking how the hell did you get a rectangle of flow into an area that is a cylinder ;p didn't drink *that* much y'know

[flamerz14]

ARRGGHHH. I hate maths.and i'm only 14. joo makes me miserable..so simple conclusion:

1.the smaller the pilot volume the better
2.light pistons are good
3.equilisation holes are for airtight pistons and should be <5mm

last one not complete... 1/4 or 3/4?

[Modderxtrordanare]

1.the smaller the pilot volume the better
2.light pistons are good
3.equilisation holes are for airtight pistons and should be <5mm

Equalization holes should actually be just small enough as to have a smaller flow rate than that of your filling valve. (i.e. Schrader)

The 1/4 caliber = ideal piston travel distance is correct, as Jack both stated and proved. (Albeit with his nasty hang-over.)

[jackssmirkingrevenge]

(Albeit with his nasty hang-over.)

Feeling a lot better now, cheers good to be back home and on my own PC, instead of having to share an internet cafe with drooling perverts browsing porn and death-mutes having animated webcam conversations that look like their trying to defend themselves from a particularly visciois swarm of wasps.

and flamerz, yeah, what Modder said