flow of air inside a PCP

[Atom]

For more efficiency make a SSG (anti bounce hammer) for more power put longer pin. The pin exits the valve only 2.3 mm...

[rsterne]

2.3 mm should be plenty of travel for the valve stem.... If you are using that much valve travel, your gun will be VERY inefficient.... Typical PCPs, properly tuned have a valve lift of only about 1/4 of the throat diameter or less.... Anything approaching 1/2 the throat diameter and you are shooting an air hog....

Bob

[Atom]

If you want to reduce power make HST (hammer spring tension) or make shorter springs. The weight of the hammer is 33 grams. Orginal spring dimensions OD 9.8 mm x 89 mm x  1 mm, 23 active coils 25 total...

[rumbleUU]

looking at those loooong valvepins, geek, 

Im sure you bob has some answer to this: if a typical unregulated pcp like the 900W 5.5mm has everything same size hole(lets say 3.5mm), and its only regulated by the transfer port hole, how does the curve for power/efficency look when going from small (1mm) to big (3.5mm) TP hole, is it linear?

What I know is 1mm TP hole=10 joule, and from reading here it seems 3.5mm TP hole=40 joule, then what is to expect from 1.5, 2, 2.5 and 3mm TP hole in Power? and how does the efficency go with that, does it gets better with bigger TP hole?

[Atom]

2.3 mm should be plenty of travel for the valve stem.... If you are using that much valve travel, your gun will be VERY inefficient.... Typical PCPs, properly tuned have a valve lift of only about 1/4 of the throat diameter or less.... Anything approaching 1/2 the throat diameter and you are shooting an air hog....

Bob

Mr.Bob how much pin should max. exit the valve in mm?

[rsterne]

Roughly speaking, with everything else remaining the same, the maximum FPE is proportional to the transfer port (smallest port) diameter.... Note I said MAXIMUM, which means a shot where the valve is open until the pellet exits the muzzle.... If the shot is limited by valve dwell, that no longer applies....

The efficiency at constant FPE and pressure will favour the larger transfer port, because that allows you to use less valve dwell.... You are flowing more air in a shorter time.... If on the other hand you are comparing the efficiency at maximum power (dwell long enough that pellet exits the muzzle), you will likely find the opposite, and the efficiency will increase as the power decreases with smaller ports....

The valve stem only needs to protrude from the back of the valve about 1/2 the valve throat diameter, because in proper tunes you will only need about half that in valve lift.... However, if you are trying for maximum power for bragging rights, you may want to allow a bit more than that, so that the hammer never hits the back of the valve.... About 3/4 of the throat diameter is plenty.... Just remember you won't actually use that much for normal tunes, because if you do the efficiency will be terrible, and the gun will be an air hog....

Bob

[Atom]

Roughly speaking, with everything else remaining the same, the maximum FPE is proportional to the transfer port (smallest port) diameter.... Note I said MAXIMUM, which means a shot where the valve is open until the pellet exits the muzzle.... If the shot is limited by valve dwell, that no longer applies....

The efficiency at constant FPE and pressure will favour the larger transfer port, because that allows you to use less valve dwell.... You are flowing more air in a shorter time.... If on the other hand you are comparing the efficiency at maximum power (dwell long enough that pellet exits the muzzle), you will likely find the opposite, and the efficiency will increase as the power decreases with smaller ports....

The valve stem only needs to protrude from the back of the valve about 1/2 the valve throat diameter, because in proper tunes you will only need about half that in valve lift.... However, if you are trying for maximum power for bragging rights, you may want to allow a bit more than that, so that the hammer never hits the back of the valve.... About 3/4 of the throat diameter is plenty.... Just remember you won't actually use that much for normal tunes, because if you do the efficiency will be terrible, and the gun will be an air hog....

Bob

Valve throat is 6 mm, means 3mm max. thank you

[rsterne]

It means that a proper, operating tune will require only about 1.5 mm of valve lift or less, so that 2.3 mm is fine for the way you will end up tuning the gun.... If you are looking for maximum power (which you will then never actually use), then you may use about 3 mm of lift.... To insure that the hammer never hits the back of the valve, you may need more than that so you don't see strange things in testing, like increased hammer strike causing decreased velocity when you are trying for maximum power....

If I were designing a valve with a 6mm throat, I would allow for 4 mm of stem travel, knowing that I will then have plenty.... However, I would expect that the 2.3 mm you now have would produce exactly the same results, once the gun is properly tuned.... Don't forget that lengthening the valve stem decreases the hammer stroke.... If the gun is already hard to cock you will make that even more of an issue, because you will need a stiffer hammer spring because of the reduced hammer travel.... If that is not an issue, then a bit less hammer stroke won't matter, of course....

I presented this argument about valve stem length because it is a common error that people think that making it longer will allow the valve to open further and give move power.... It is a rare gun indeed where it actually doesn't have enough valve stem travel.... Most of the time, fitting a longer stem results in a decrease in power, because of the reduced hammer strike.... I was trying to save you the headache of finding that out and wondering what happened....

Bob

[Atom]

 Bob Sterne,my deep respect for your lifework in the airguns world...

[rumbleUU]

very well explained, still learning

But is it possible for a "tune" with all holes wide open let say 3.5mm all the way, and a very weak tension OR a weak spring behind the hammer to get more efficiency compared to  a restriction in TP hole of 1mm and a harder hammer tension.... reason asking is cause here all airguns have 1mm TP hole, big hammerweights and strong hammersprings, so you need to strike that valvepin hard to get that 10 joule, I think that the other way around may increase the efficency? bigger TP hole instead of the small 1mm and less tension or weaker hammerspring to still be max 10 joule but hopefully increase efficency?