Ignorant question ? ... Or valid statement ?

[Motorhead]

PCP arms are HPA arms .... and both generally use a REGULATOR upstream of valve system.

In talking HPA conversions on QB's it keeps getting stressed a 1800# burst disk be installed downstream of regulator, and justly so !!

Do we have any idea what is the internal valve pressure in the more common PCP arms ?
Pretty sure with 2000-3000# fill pressure within tank the valve is NOT seeing that # and it is much less to prevent valve lock ?

In application ALL the PCP/HPA/Co2/Pump pneumatics all use a spring Loaded striker/Hammer hitting a poppet valve.
The size of valve, hammer weight etc differ pending gas pressure present within valve assm.

What I'm eluding too is they all are in the same basic family on how they operate ... am I wrong here ?

[bstaley]

Most PCPs are not regulated and the valve is at full fill pressure.

[Ribbonstone]

Most PCPs are non regulated, so to get a good shot count, have to have a valve that somewhat self regulates.  Good design can run and a very consistent velocity over a wide pressure range. A PCP's tank is every decreasing in pressure...each shot lets a little out, and the pressure to the valve decreases.

Regulated guns deliver air at the same pressure to the valve throughout.  Valve doesn't have to be designed or tuned to work well over a range of pressures, just work well at that one pressure.

So, yes they both work the same way...a weight (striker or hammer) smacked against a valve stem, knocking the valve open to let loose a burst of air.

[rsterne]

Yup, PCP, MSP, SSP (and CO2) are all pneumatics, and most rely on a hammer striking a poppet valve to release the air.... In the "pumpers" it is generally a "dump shot" ie all the air in the valve is released, although a few are set up for "retained air" and only release some of it on the first shot.... and you can either top up the valve or get a second (or third) shot.... In CO2, most (if not all) of the CO2 in the valve is released with each shot, and replenished between shots.... In high powered CO2 guns, where the valve is opened up for increased flow INTO the valve this is not the case, and they act more like a regulated PCP.... releasing a measured blast each shot....

Most PCPs are, in fact not regulated, and the valve is operating in a balancing act between being opened by the hammer and being slammed shut again by the air (the valve spring does little).... At the higher pressures, the pellet is receiving a short, high pressure blast of air.... and as the pressure drops the valve opens longer/farther and the pellet sees more air but at lower pressure.... Eventully the velocity peaks, and shortly after that the valve stops opening more and as the pressure drops so does the velocity.... That is the reason for the classic "bell curve" shape of a shot string on a non-regulated PCP.... Regulated PCPs just operate at one particular "balance" all the time, as long at the tank pressure is above the regulator setpoint....

Bob

[Motorhead]

Interesting ... simply WOW, that the poppet valve of a pcp is burping such HIGH pressure !!
More I wrap my mind around the 3 basic operating systems, PCP, Pump pneumatic and HPA more I find myself seeing the light of which one has the overall simplest and most controllable parameters for consistent velocity and ease of changing performance .... Regulated HPA  

[rsterne]

That's true, but it is very important to have enough volume between the regulator and the valve seat so that the AVERAGE air pressure in the valve during the shot is as high as possible.... I have a rough rule of thumb of 1 cc per FPE that you want the gun to produce.... As the volume gets smaller, the average pressure decreases.... because the regulator can't act quickly enough to top it up.... Basically, what air you start with in the valve is what you have to deal with.... Related to this is how the air between the regulator and the valve can get INTO the valve.... If it can't (easily) then only the air in the valve matters.... Generally this is relatively small, and it will restrict the power.... &^%$# "XP Tuned Valve" has slots milled in it to allow more air into the valve than can get out (hopefully) so it can produce more power.... Study that thread I pointed you to earlier, there is a LOT of information there.... If you have any specific questions, just ask....

Regulators have their liimitations, too.... They prevent you from benefitting from the higher efficency of the higher pressures in a non-regulated PCP.... The first few shots in a non-regulated gun may be as much as twice as efficient as the last few (and the rest are in between).... How much energy you can get out (in FPE) for each CI of air you use is important, and one of the things I spend a lot of time on.... Lots of variables.... lots of fun dscovering how they interrelate....

Bob

[Motorhead]

That's true, but it is very important to have enough volume between the regulator and the valve seat so that the AVERAGE air pressure in the valve during the shot is as high as possible.... I have a rough rule of thumb of 1 cc per FPE that you want the gun to produce.... As the volume gets smaller, the average pressure decreases.... because the regulator can't act quickly enough to top it up.... Basically, what air you start with in the valve is what you have to deal with.... Related to this is how the air between the regulator and the valve can get INTO the valve.... If it can't (easily) then only the air in the valve matters.... Generally this is relatively small, and it will restrict the power.... &^%$# "XP Tuned Valve" has slots milled in it to allow more air into the valve than can get out (hopefully) so it can produce more power.... Study that thread I pointed you to earlier, there is a LOT of information there.... If you have any specific questions, just ask....

Regulators have their liimitations, too.... They prevent you from benefitting from the higher efficency of the higher pressures in a non-regulated PCP.... The first few shots in a non-regulated gun may be as much as twice as efficient as the last few (and the rest are in between).... How much energy you can get out (in FPE) for each CI of air you use is important, and one of the things I spend a lot of time on.... Lots of variables.... lots of fun dscovering how they interrelate....

Bob

That said ... your QB78 too QB79 valve/tube volume issues addressed make perfect sense.

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On another note, would one assume with HPA systems in use having 4500# in storage that a regulated down too 2500# give or take pressures is only a matter of time it gets applied to hand held regulated PCP weapons ?
If the efficiency and performance is greater popping off sips of such high pressure, it would seem logical to store higher yet pressure and get multi shot consistency by using a regulated down lesser pressure.
Same as we do now and really only differing in the fact we always want MORE !!

[rsterne]

Walther Dominator 1250.... It has a 300 bar (4350 psi) air reservoir and the regulator is set for about 2200 psi.... Unfortunately, the regulator is built right into the valve, which severely limits the power.... The guys converting the nearly identical RWS/Hammerli 850 to HPA are getting the same power and a higher shot count from roughly the same weight gun.... using a 3000 psi 22 CI tank regulated at 1700-1800.... The reservoir on the 1250 is heavy (steel and thick)....

The limiting factor presently, IMO, is the weight of the "tank" for 4500 psi.... Nobody is (as yet) making carbon wrapped tubes that are strong and light.... I think one of the problems may be damaging them in the field by dropping the rifle, etc.... A ding in a carbon wrapped tube means you throw it away.... Someday we will see this, when the technology (and the price) catches up with the designers....

Have you seen my "Hayabusa" project?.... You might find it interesting.... http://www.gatewaytoairguns.org/GTA/index.php/topic,9588.0.html

Bob