I don't believe a TP smaller than 3.0mm ever works in a 12FP springer....

[Barryg]

I just don't think it can flow properly and make the power... irrespective of length etc, I've never found anything less that 3.0mm to be efficient, and generally unless the port is exceptionally long (like an LGV), 3.2 is a more usual minimum starting point.

Even 25mm cylinder guns with fairly heavy pistons found 3.0mm too tight, and had to open out to 3.2. And larger bores 26/28/30 3.2 is always too small.

Discuss.

What is the factory 80 size?

[les allam]

What is the factory 80 size?

I think the 80 has a 2.8mm TP standard from the factory, two of mine do.
Les..

[les allam]

Out of interest what size TP as the AA Pro/elite got ?.
Les..

[trajectory]

This has the makings of an interesting thread. I'd like to try & get an understanding of how the variables interact with one another.

Noticed a comment "The flow rate calculator in the link is for fluids, not air."earlier on in the discussion but isn't air classed as a fluid? I think all gasses are regarded a fluids. They are complex in some respects as they are compressible fluids as opposed to liquid fluids which are generally regarded as incompressible.

Looking forward to learning a bit about flow rates & fluid dynamics....

[BTDT]

This has the makings of an interesting thread. I'd like to try & get an understanding of how the variables interact with one another.

Noticed a comment "The flow rate calculator in the link is for fluids, not air."earlier on in the discussion but isn't air classed as a fluid? I think all gasses are regarded a fluids. They are complex in some respects as they are compressible fluids as opposed to liquid fluids which are generally regarded as incompressible.

Looking forward to learning a bit about flow rates & fluid dynamics....

Gasses are indeed regarded as fluids but, being compressible, will behave very differently in a transfer port.

The flow rate link would be spot on if we filled our springer cylinders with water, though.

[cooper_dan]

My bachelor's and master's dissertation were based around fluid dynamics, simulation and modelling. One on IC cylinder head flow and one on external aerodynamics. Can be very interesting, but when it comes to transfer ports I would just stick with physical testing. Too many variables and life is too short

[TonyL]

I have three formulae for transfer port diameter, and they never agree with each other

There's too many unknowns to make such calculations reliable.

My bachelor's and master's dissertation were based around fluid dynamics, simulation and modelling. One on IC cylinder head flow and one on external aerodynamics. Can be very interesting, but when it comes to transfer ports I would just stick with physical testing. Too many variables and life is too short

Yes, this.

[Gunfun]

Gasses are indeed regarded as fluids but, being compressible, will behave very differently in a transfer port.

The flow rate link would be spot on if we filled our springer cylinders with water, though.

The more I look at tuning springers, the more mind boggling it becomes.

[trajectory]

When writing my earlier post the idea of filling the cylinder ahead of the piston with water crossed my mind too. I thought if I suggested it someone might say'ok, you first' & I wouldn't fancy trying to dry out intrrnals of a springer, even a clunker of a springer. Still as a theoretical model it would be interesting if the weight of the fluid could somehow be factored out & the empirical perfomance evaluated with changes being introduced step by step so the effects of them could be measured. It would take out any varriability arising from the clmpressability of the air. But how it would translate into the real world is anyones guess so I think the advice that life is too short & its probably better to just roll up your sleeves & get cracking ks good advice.

It will be interesting to see any results from those that have carried them out.......standard rifle v port diameter, differant stroke v port diameter or variability with port volume etc. Its a big topic........but very interesting.

[cringe]

I was thinking about making a brass insert as a transfer port, my idea is to make it tapered down from compression tube, with a convex entry, so no sharp corners, highly polished [mirror]. My theory is based on - as a youth I used to polish cylinder head ports on my motor bikes & it did improve performance - better intake/exhaust flow. just an idea at the moment?

PS. in engineering terms the word fluidic covers both liquid & gas.

[HW777]

Gasses are indeed regarded as fluids but, being compressible, will behave very differently in a transfer port.

The flow rate link would be spot on if we filled our springer cylinders with water, though.

A springer filled with water, I wonder what the range would be

[Phil Russell]

A springer filled with water, I wonder what the range would be

Crikey, can't resist this. When I was knee high to Ronnie Corbett I had an air rifle ... well maybe I should say 'we had' because my friend and I both used it. No idea where it came from or what it was, maybe a Wobbly Jaguar or a Diana 15/16? I remember firing nails, cocktail sticks and potato bits and ..... don't know how, but using it as a water pistol. It wasn't very good. I can't remember how we loaded it. Maybe trickled water in as we cocked it? We did suss that it needed oiling after a few shots though...
Oh the things you do in the innocence of (very) youth.
Cheers, Phil

[Shed tuner]

Out of interest what size TP as the AA Pro/elite got ?.
Les..

3.0 x 15mm, and it's too small, even when the bore is reduced down to 25mm. TOok that one out to 3.2, but the accelerometer data indicates it shoudl be opened up a little more.

I'll be doing some experiments with my FAC one next year - I don't have all the tools and equipment with me on this trip - or even a shrono. Will also bring a machined lighter piston. However I have no doubt that 3.0 will be too small for a 30mm tube... 3.4 woudl be my guess..

[les allam]

3.0 x 15mm, and it's too small, even when the bore is reduced down to 25mm. TOok that one out to 3.2, but the accelerometer data indicates it shoudl be opened up a little more.

I'll be doing some experiments with my FAC one next year - I don't have all the tools and equipment with me on this trip - or even a shrono. Will also bring a machined lighter piston. However I have no doubt that 3.0 will be too small for a 30mm tube... 3.4 woudl be my guess..

Thanks for the reply.
Like you,I have a reduced cylinder PE with standard TP, I am happy with the way my one performs.
What would I gain from opening up the TP on my gun ?, reduced recoil?.
Les..

[Shed tuner]

Thanks for the reply.
Like you,I have a reduced cylinder PE with standard TP, I am happy with the way my one performs.
What would I gain from opening up the TP on my gun ?, reduced recoil?.
Les..

reduced piston bounce, which then allows for less spring, and therefore less recoil (yes, there's more to it, but basically...).