I hear about the QB78 and 79 or other guns converted to HPA or PCP. Please for an educational basis discuss the three co2, hpa, pcp. and also bulk fill. know it sounds stupid but I am new to airguns and only own springers.
hi-it does NOT sound stupid. you are new and curious. welcome.
HPA is high pressure air. PCP is pre-charged pneumatic. same thing
co2 is carbon dioxide, those little 3" cylinders (for instance) or the larger 9oz, 12 oz or bigger paintball tanks which you can refill or have refilled at a paintball shop
springers you know about. the spring pushes air which pushes the bb or pellet
multi-pump is a common type where you can pump the gun 1 to ten times (more or less) for one shot, with varying velocity
multi pump is tiresome to some people, co2 is very convenient, but costly in the little cylinders, and is not much good below 45 degrees F because it needs to be warmer (up to about 95, at which point it can act funny) to give adequate pressure. having a 9oz paintball tank refilled can cost maybe 25c/ounce, so it's pretty cheap and you get a lot of shots (sometimes over 600) per tank
HPA gives more power, fewer shots and requires scuba tanks, or an expensive compressor, or an expensive and tiresome hand pump, and although that sounds like a lot of negatives, it seems to be the most popular propellant system (go to what's called the yellow forum to see lots of people who love their hpa guns)
co2, springers,and multi-pump pneumatics are (can be) cheap. most hpas will cost $400 and up, and the charging system(s) can be involved and costly, but people seem to love them.
i like co2 and springers. no two people are alike--here or anywhere else.
All three have a volume of compressed gas that the valve taps a little from on each shot. the mechanics of the gun are pretty much the sam (striker smacking a valve stem, valve opening and returning closed, gas being released during the time the valve is open).
CO2's pressure depends on temperature, the cooler it is the lower the gas pressure. Lets call it 700psi in cold/cool weather to about 1200psi in the middle 90's. In very cold weather, co2's pressure gets much lower than 700psi and much higher in very hot weather. Co2 under compression is partly a liquid. As you use a little gas for a shot, some of the liquid converts to gas, so the pressure in the system stays pretty constant (if you keep the temperature stable, co2 will have the same pressure or as long as there is some liquid in the system).
Co2 is also "thicker" than air, so even at the same pressure as a gun running on air, it will deliver a bit less pellet spee than air (which we can consider as being "thinner" and flowing more easily).
Unlike co2, compressed air is much-much less temperature sensitive.
Hard to divide PCP and HPA. For QB's, HPA would be the attachment of a paintball type regulated air tank to feed air into the gun in place of co2. These tanks can be had with regulators delivering various pressures of air, with 800-850PSi being the most common for paintball use (although many paintball guns are going to lower pressure operation). Can buy them with regulators set for higher pressures (but probably wise NOT to go above warm weather co2 pressures).
These HPA tank regulators only let out a specific pressure of air. With a 3,000PSi tank and a regulator set for 850PSI, all the tank will deliver to the gun is 850PSi. In that respect, HPA is like co2 in that the pressure to the valve is the same shot after shot.
PCP's have the rifle holding high rpessure inside itself. With a QB, better to have a PCP designed tube that is designed to hold this higher pressure (2000psi to 3000psi, depending on the rating of the tube). This has the potential for very high speeds, but each shot taps off some of that air, so each shot lowers the pressure in the gun by a little bit.
Valves have a range at which they can more or less self adjust. Air pressure on one side holding the valve closed, striker hitting the valve stem forcing it open. There will be a range (usually called the "sweet spot") of pressure where the forces are in balance, and vel. stays stable.
Energy/speed wise, can think of it as follows:
PCP: max speed, fewest consistent vel. shots.
HPA: high speed, good number of consistent shots.
CO2: lower speeds, but a whole lot of consistent shots (so long as you keep the temperature stable).
This message has been edited by gubb33ps on Jan 28, 2010 9:25 PM
On a QB, the bulk fill adaptor replaces the 12gr. end cap. Bulk fill end cap has a foster nipple on it, and inside there is a one-way valve (gas can go in, but can't come out). So a bulk fill end cap lets you gas the gun up from a larger co2 tank (by way of a hose that snaps onto that foster nipple), "bulk filling" without the use of 12gr. cartridges.
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