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WARPIG Tech Talk - Autococker / Minicocker

Terminology is Confusing Me.

In Reply to: low pressure chamber posted by Mike Roch on July 07, 2003 at 20:50:14:


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Posted by:
Dale "Head_Hunters" DuPont
on July 09, 2003 at 11:13:10

"what would bying a low pressure chamber or a volumizer do for my gun and how would i install it"

Low Pressure Chambers and Volumizers

The term 'Low Pressure Chamber' was first seen by me as a part name / marketing term for the Spyder. The hollow tube extension sticking out forward of where the vertical ASA is located just in front of the trigger.

It has no function unless you put a low pressure regulator and low pressure valve and spring set on the marker. Kingman was using the magic word 'low pressure' to sucker some Newbies into buying their product... Along with 'mini expansion chamber' 'power feed' 'custom this or that' Just words with no function that sound like terms used in reference to higher end markers. The 'rear cocking bolt' just imitates an autococker for example.

I have seen the term 'volumizer' is used most often in reference to the autococker.

Both add volume between the valve and the air regulator output. With the exception of the Shutter, Spyders have no regulator 'lower' pressure air supply. Hence no function.

The function of a 'volumizer' is a modification sometimes needed for Very Low Pressure Autocockers in the sub 300 psi range.

They are most often used as a modification for OLDER Autocockers which have a smaller internal volume than the newer (2K and later) autocockers. Adding a volumizer was cheaper than having the receiver and front block machined out.

The newer autocockers rarely actually NEED a volumizer.

The goal for many is to have the lowest operating pressure (determined by the regulator setting,) AND sufficient air flow through the valve to accelerate the ball up to 300 fps.

That can result in a real quiet autococker and 'braggin' rights' but CAN result in wasted air and inefficient air supply use.


To accomplish this you need to do several things.

1. The valve open duration time has to be open LONG enough to pass the air volume needed through the valve to accelerate the ball up to speed.

If it is too short, you can't get the ball up to speed. (Velocity screw and hammer spring pressure) If it is open too long, the ball is long gone and you are wasting air and making noise.

2. The air passing through the valve is under pressure and EXPANDING. You have to have enough TOTAL VOLUME behind the valve to start with.

If the TOTAL VOLUME expanding through the valve is not adequate, you can't get the ball up to 300 fps speed. If the TOTAL VOLUME expanding through the valve is too large then you have a ball in excess of 300 fps OR wasting air if the ball has already left the barrel.

NEXT, TIMING is EVERYTHING and I'm not talking about timing an autococker here.

3. You have to have sufficient PRESSURE behind the valve so it can pass enough Total Volume expanding through the valve, in the TIME AVAILABLE for the ball to accelerate up to speed in the barrel. Air that passes after the ball enters the ported section and leaves the barrel entirely is wasted air.

The length of the unported section and the drag largely determines the TIME AVAILABLE on the ball while passing though the ported section.

And, of course, the valve open duration.

The longer the unported section, the more TIME you have to accelerate the ball. That is why the paintball cannons on the tanks with 8 foot long barrels can run at 80 psi.

The total VOLUME of AIR that is AVAILABLE that can expand to atmospheric pressure inside the barrel is determined by the Original Volume behind the valve AND the PRESSURE it is under.

You lower the pressure and you lower the total volume available.

A volumizer compensates by adding additional Volume, which increases the Total Volume available to expand.

Any excess volume that flows through the valve, barrel porting, and barrel muzzle AFTER the ball has left the marker is wasted air.

All of these variables combining together determine your "Efficiency". Efficiency is the total number of shots you can fire on one tank of air.

The LP valve can only stay open for a maximum duration before the valve return spring and air flow from the regulator slams it shut. The valve spring force is constant but be aware that a regulator set at 500 psi with assists the valve to shut FASTER than a regulator set at 250 psi.

The regulator is relatively SLOW to refill the chamber behind the valve OR to keep pace with the flow VOLUME capable of going through the open valve. It can lag behind the valve at very high rates of fire as in 12+ RPS. Not a factor in the real world with a finger pulling the trigger.

Shootdown is NOT a product of whether or not you have a volumizer but simply if your regulator can REPLACE the air used by the last shot BEFORE you fire the next shot. That would ALSO require that the pressure behind the valve would have to be the same to accomplish "replacing" the air.

Now, What would happen if you had a volumizer that provided more Total Volume than you could ever use? One say about the size of a gallon milk jug.
Nothing. A fraction would go through the valve and the excess would have no effect. The valve is the limiting flow factor.

So what would happen if you put on a volumizer that you didn't really need. Nothing except you have less $money.

So HOW can you tell IF a volumizer would actually improve they performance of your marker and reach you low pressure goals?

Spend the money and put one on. Make No changes other than the volumizer.

Chrono your marker and record the muzzle velocity of a 5 shot sample of balls. Put the volumizer on and chrono another 5 shot sample. Compare.

If there is NO CHANGE, you didn't need one. You already have excess volume available behind the valve.

If it Increases your muzzle velocity, you did need one.

Now lower your operating pressure 25 psi and do another 5 shot sample. What would happen to the muzzle velocity if the volumizer were beneficial at the lower operating pressure?

If the muzzle velocity increases, you benefited. You have lower operating pressure and can back off the velocity screw some and still generate 300 fps.

If the muzzle velocity lowers, then MAYBE you benefited if you can adjust your velocity screw in and still generate 300 fps. You have lowered operating pressure and still generate 300 fps.

Repeat until you stop getting any measurable benefits. Now you can change the valve duration open time as well. A softer valve return spring. If your velocity screw is turned in all the way, a firmer hammer spring might be called for.

Valve open duration is the RELATIVE balance between the valve return spring and the hammer spring. If increase the valve duration time open has no effect on velocity, then you are wasting air and efficiency. The ball is long gone with the valve still passing air through it.

BUT VOLUMIZERS are EXPENSIVE!
I don't want to be out the money with no benefit.

Get a Cheap ONE. How about spending $5 for an ugly one? If it works, you can cough up the money for the stainless steel one...

Here is how. Remove the plug in the bottom of the front block. Add volume there by screwing in a hollow piece of pipe with a cap on the end.

The thread is 1/4" NPT. A standard pipe thread that is available at your local hardware store. Buy a 3" - 4" pipe threaded on both ends and add a cap to plug the open end.

If you want to get fancy, buy a union and use your air pressure gauge to be the 'plug'. You need to have or install a gauge anyway IF you plan on adjusting your regulator properly.

Words of caution, remember these are pressurized systems and the pipe has to be rated for the pressures you are using. Brass or Steel. I wouldn't hook one up to 900 psi if it weren’t rated for it. Nor 300 psi. Nor 200 psi.

Tip: A Smart Parts Mini Gauge (0-600 psi or 1200 psi)is 1" in diameter and can be installed directly into the front block plug hole facing down and NOT have clearance problems with the regulator.

A larger, standard gauge WILL have clearance problems unless you install a 90 degree elbow so the gauge faces Right or Left. Or Forwards for that matter.

All the autococker gauges I know about have the same 1/4" NPT pipe thread.


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