How big should a transfer port be...?

[DedIdick]

Exactly my point, the PIAT doesn't even bother with half the compression cylinder, allowing free circulation of air. They're called AIR guns, the clue is in the name, why restrict it?

I agree with you, see post #2

But then again I was a steam engineer, we only throttled the steam to slow things down.

[Shed tuner]

Exactly my point, the PIAT doesn't even bother with half the compression cylinder, allowing free circulation of air. They're called AIR guns, the clue is in the name, why restrict it?

stop baiting the natives

[BTDT]

That's a very interesting article you have written on this topic in October's Airgun World Jim.

Must admit I'm a loyal fan of leather washers. I have bought and stripped vintage airguns that are decades old and congealed grease and oil have preserved the ancient leather washers. I only replace them if they crumble and some of my prewar BSAs still have their original leather washers in place. OK so performance may not be as high as it could be but cocking stroke and shot cycle are smooth enough to obtain accurate performance at realistic open sight distances. Plus, they're original to the guns, so if they still function - in situ they'll stay

Kind regards,

John

Thank you, John.

The one instance when larger diameter transfer ports are beneficial is when fitted to short piston stroke guns that rely on autoignition for their muzzle energy. The autoignition creates a pressure and temperature (the air's internal kinetic energy) spike, that gets the pellet moving earlier in the piston stroke, so that the pellet and piston are traveling in the same direction (the 'cylinder pulse', when the pellet gains most energy) for longer.

Transfer port diameter comes into the mix because the wider it is, the later in the still short cylinder pulse the transfer port flow chokes.

That's why the leather piston seal HW35 had a wide (4mm?) transfer port, but the later synthetic seal version had a much narrower (nearer 3mm?) port, and probably a bit longer stroke.

[TonyL]

Due to a hectic home schedule at the moment I haven't got as far as reading your excellent looking (again) article this month. Very much looking forward to it, as always.

Those TP diameters are as I understand them to be and the stroke on the factory synthetic sealed versions is, indeed, longer, to the tune of 4 to 5mm.

And I can also sympathise with John's observation on keeping the seal leather on certain guns, retaining the original character, originality and the all-important aroma.

As always, some most excellent articles coming from you chaps in these troubled times, keeping us distracted and entertained.

[richtel]

Interesting thread here-

https://www.pyramydair.com/blog/2008...r-port-part-1/

https://www.pyramydair.com/blog/2008...r-port-part-2/

https://www.pyramydair.com/blog/2008...r-port-part-3/

[Barryg]

Does anyone know of a springer that has a better transfer port than this one or is it the best ever? just wondering

[jjjohn]

The seller has a couple of decent stocks listed as well.

[evert]

Does anyone know of a springer that has a better transfer port than this one or is it the best ever? just wondering

Which gun is that? Some Diana?

[Shed tuner]

Diana transfer port arangement probably is the most efficient factory arrangment I've seen - coupled with a 28mm bore and a long stroke, this is what makes them great for FAC power levels.

FWB300 TP is similar. HW 77/97 is good, but longer; TX longer still (and not such a good sealing arrangement), but can be shortened.

[Barryg]

Diana transfer port arangement probably is the most efficient factory arrangment I've seen - coupled with a 28mm bore and a long stroke, this is what makes them great for FAC power levels.

FWB300 TP is similar. HW 77/97 is good, but longer; TX longer still (and not such a good sealing arrangement), but can be shortened.

It's interesting that you like the 77/97 T/P being offset but I was also wondering why you think the HW is a better sealing arrangement than the TX.

It's also interesting that the more modern Diana the 460 has a offset T/P that has another 15mm more stroke than the 52 and only just has a little more power than the efficient 52 just so it can have a barrel inline with the cylinder like the 77/97 and I would guess it would be harder to machine. Anyway interesting subject

[NickG]

The problem with the tx set up imo is the 2 o rings , and not so much the length ( long ports give soft cycle),I believe AA use 2 o rings to allow for more flexibility in the design to take up slack in the lock up , due to manufacturing tolerances, some lock up well some don't. The down side of this slack is the transfer port can hammer the end of the barrel, in severe cases it closes the lead in up slightly, which then sizes the pellet down ruining both accuracy and power.
When I make my own comp tubes I seal them in a completely different manner.

[Shed tuner]

The problem with the tx set up imo is the 2 o rings , and not so much the length ( long ports give soft cycle),I believe AA use 2 o rings to allow for more flexibility in the design to take up slack in the lock up , due to manufacturing tolerances, some lock up well some don't. The down side of this slack is the transfer port can hammer the end of the barrel, in severe cases it closes the lead in up slightly, which then sizes the pellet down ruining both accuracy and power.
When I make my own comp tubes I seal them in a completely different manner.

yup. replacing the 2 o-rings with a solid type seal can help.

Also I did a thread a while back on the bam 40 copy of the TX.. it has a FWB 300 type seal in there - a much better system.

[Barryg]

The problem with the tx set up imo is the 2 o rings , and not so much the length ( long ports give soft cycle),I believe AA use 2 o rings to allow for more flexibility in the design to take up slack in the lock up , due to manufacturing tolerances, some lock up well some don't. The down side of this slack is the transfer port can hammer the end of the barrel, in severe cases it closes the lead in up slightly, which then sizes the pellet down ruining both accuracy and power.
When I make my own comp tubes I seal them in a completely different manner.

Correct me if I am misunderstanding what you are saying guns like the 77/97 and the Diana 460 are buffered by the front of the cylinder metal to metal with a small gap for the seal and T/P once the cylinder is fully forward, but the TX the seals are the buffer because there is a nut and not a flat surface like where the other two are buffered, you can see in the pics where the hinge pin bolt hole has made a mark on the 460 this couldn't happen with the TX nut.
I think that I disagree about the slack on the TX as I think the TX is supposed to have slack in that area otherwise it would put strain on the cocking link like it can on the 77/97 and crack if it's to tight, I don't really like the slack but these designs where before spring closing breeches

[NickG]

The slack doesn't protect, the lever,the clearance at the rear of the cocking shoe dies that .

[Barryg]

The slack doesn't protect, the lever,the clearance at the rear of the cocking shoe dies that .

But isn't it the clearance ( the loose shoe ) that causes most of the slack?