QB efficiency tune?

QB efficiency tune?

Joined: June 7th, 2010, 12:14 am

August 4th, 2010, 1:02 am #1

Though I have swept the form pages pretty carefully, I have not found reference to what might be termed an efficiency tune for the QB series running on CO2.

Robert has done a grand job of the topic in HPA.

Woulds any care to enlighten me?

Parameters? "useful power and accuracy enough to make for enjoyable 25 meter shooting.
\

TIA

Cal
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Joined: November 17th, 2006, 3:51 am

August 4th, 2010, 1:30 am #2

Find that once you slow the striker speed down a whole bunch (looking for a light valve hit and low vel.) the strikers hit becomes more variable. At slow speeds, friction seems to be more variable, so the strength of the strike goes up and down, giving erratic vel. numbers.

So I looked at ways of conserving gas by still keeping a decently fast striker travel.

#1. Lighten the striker. A light fast striker uses less gas than a slow heavy one, but gives a good smack to the valve. May be a slight friction bonus at work as well; usually, lighter strikers have less bearing area on the tube, so less friction.

(Havent gotten around to this yet, but I will sooner or later thinking about slightly reducing the diameter of the striker and using old-school buttons like what has been done on springer pistons. Looking to cut variable friction, make for a more uniform strike.)

#2. Strangle off the gas flow at the transfer port. Made some little brass top hat type inserts that fit into icemaker hose. The top hat flange is on the bottom, to keep the thing from being squirted through the transfer port. Thicker walled tubing would make this easier, but I havent run across any.
This one is ugly, but functional:
[/IMG]

Is also one of the reasons the old Crosman 2000 got so many shots from one 12gr. The transfer port in the valve is tiny and the valve stem seal (see #3) a closer fit to the inside walls of the valve.
[/IMG]

#3. Strangle off the gas flow in the valve itself. Gas has got to flow between the valve stem and the side walls of the valve. If you make a larger diameter valve stem seal, there is less room for the gas to flow around, and the vel. drops. Have had Crosman valves that had a brass insert to decrease that flow around the valve stem, but generally its easier to make a fatter valve stem seal.

Larger also gets more closing force from the pressurized gas, which usually makes for a faster dwell time (valve opens and shuts faster).

This one is unfinished, but of about standard diameter. Can see the space around with the gas has to flow to get to the barrel. If the white valve seal material were made fatter would let less gas out per shot.
[/IMG]
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Joined: January 9th, 2005, 1:46 am

August 4th, 2010, 1:39 am #3

Though I have swept the form pages pretty carefully, I have not found reference to what might be termed an efficiency tune for the QB series running on CO2.

Robert has done a grand job of the topic in HPA.

Woulds any care to enlighten me?

Parameters? "useful power and accuracy enough to make for enjoyable 25 meter shooting.
\

TIA

Cal
Cal,

In a few weeks we will have the QB78 Hammer De-bounce Device designed by Steve Woodward in stock at Archer Airguns. Tests so far have shown that this provides much greater operating efficiency with about 50% more shots from one pair of Powerlets. The following link has details...
http://www.network54.com/Forum/113813/t ... n+QB78+HDD.

Maybe this will be of interest

Stephen Archer
Archer Airguns Inc.
Website http://www.archerairguns.com
Videos http://www.youtube.com/ArcherAirguns
Blog http://www.archerairguns.info
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Joined: June 7th, 2010, 12:14 am

August 4th, 2010, 2:24 am #4

Find that once you slow the striker speed down a whole bunch (looking for a light valve hit and low vel.) the strikers hit becomes more variable. At slow speeds, friction seems to be more variable, so the strength of the strike goes up and down, giving erratic vel. numbers.

So I looked at ways of conserving gas by still keeping a decently fast striker travel.

#1. Lighten the striker. A light fast striker uses less gas than a slow heavy one, but gives a good smack to the valve. May be a slight friction bonus at work as well; usually, lighter strikers have less bearing area on the tube, so less friction.

(Havent gotten around to this yet, but I will sooner or later thinking about slightly reducing the diameter of the striker and using old-school buttons like what has been done on springer pistons. Looking to cut variable friction, make for a more uniform strike.)

#2. Strangle off the gas flow at the transfer port. Made some little brass top hat type inserts that fit into icemaker hose. The top hat flange is on the bottom, to keep the thing from being squirted through the transfer port. Thicker walled tubing would make this easier, but I havent run across any.
This one is ugly, but functional:
[/IMG]

Is also one of the reasons the old Crosman 2000 got so many shots from one 12gr. The transfer port in the valve is tiny and the valve stem seal (see #3) a closer fit to the inside walls of the valve.
[/IMG]

#3. Strangle off the gas flow in the valve itself. Gas has got to flow between the valve stem and the side walls of the valve. If you make a larger diameter valve stem seal, there is less room for the gas to flow around, and the vel. drops. Have had Crosman valves that had a brass insert to decrease that flow around the valve stem, but generally its easier to make a fatter valve stem seal.

Larger also gets more closing force from the pressurized gas, which usually makes for a faster dwell time (valve opens and shuts faster).

This one is unfinished, but of about standard diameter. Can see the space around with the gas has to flow to get to the barrel. If the white valve seal material were made fatter would let less gas out per shot.
[/IMG]
If the restriction of the piercing pin to the valve housing bore is considered.

In unmodified form, the CO2 available is only that (relatively) contained within the valve. I have thought to "stuff" the valve body as a means of controlling gas usage.
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Joined: June 7th, 2010, 12:14 am

August 4th, 2010, 2:34 am #5

Cal,

In a few weeks we will have the QB78 Hammer De-bounce Device designed by Steve Woodward in stock at Archer Airguns. Tests so far have shown that this provides much greater operating efficiency with about 50% more shots from one pair of Powerlets. The following link has details...
http://www.network54.com/Forum/113813/t ... n+QB78+HDD.

Maybe this will be of interest

Stephen Archer
Archer Airguns Inc.
Website http://www.archerairguns.com
Videos http://www.youtube.com/ArcherAirguns
Blog http://www.archerairguns.info
Wasted gas should be eliminated if possible. There are nay sayers who site the efficiency of alternate valve designs that have no bouncing elements.
The proof of the pudding will be the tasting.

Recently I have been exploring the firing signature of the standard valve using the acoustic recording features found in softChrono.

That tool may prove useful for qualitative evaluation of a "single strike" device.
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Joined: November 17th, 2006, 3:51 am

August 4th, 2010, 2:35 am #6

If the restriction of the piercing pin to the valve housing bore is considered.

In unmodified form, the CO2 available is only that (relatively) contained within the valve. I have thought to "stuff" the valve body as a means of controlling gas usage.
The whole tube is pressurized and the hole in the valve body is a lot larger than the piercing pin that passes through. If you follow the procedure of backing off the end cap, gas still easily flows.

But the gas in the valve body is the "on deck" gas that really does the work of moving the pellet...and there is plenty of it. If you could reduce the inside volume of the valve enough, it would certainly work to slow the gun down and extend shot count. May have to try that...have an old test-bed platform QB78 running on 12grs. that might be a good candidate for that.
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Joined: June 7th, 2010, 12:14 am

August 4th, 2010, 2:42 am #7

Certainly an easy change to make.

a simple sleeve that extended the bearing surface against the pin would serve very nicely.

Oh Heck, now I'll need to get a tub of old valve parts to tinker with.
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Joined: September 21st, 2007, 12:13 pm

August 4th, 2010, 11:27 am #8

Though I have swept the form pages pretty carefully, I have not found reference to what might be termed an efficiency tune for the QB series running on CO2.

Robert has done a grand job of the topic in HPA.

Woulds any care to enlighten me?

Parameters? "useful power and accuracy enough to make for enjoyable 25 meter shooting.
\

TIA

Cal
in the right direction. Although I didn't start out to tune my .22 QB78 (bulk fill carbine)for efficiency, I lightened the striker by boring the center out to within about .080" of the nose, and turning a delrin insert filler to bring the inside back to size. The "Old School Buttons", again a good idea, although I didn't use these as yet on my QB, they did work out well on my Disco using co2.
Most of things I've done on my QB was with the idea of bringing up velocity, lightened striker, opened up valve, teflon stem, larger trans port etc. But the interesting thing is, the speed did increase, shoots JSB's 700+ fps, the shot count for a fill is up to about 70. I'd think that another good tuning addition would a spring adjuster.
Have Fun
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Joined: March 28th, 2002, 6:54 pm

August 4th, 2010, 3:29 pm #9

Though I have swept the form pages pretty carefully, I have not found reference to what might be termed an efficiency tune for the QB series running on CO2.

Robert has done a grand job of the topic in HPA.

Woulds any care to enlighten me?

Parameters? "useful power and accuracy enough to make for enjoyable 25 meter shooting.
\

TIA

Cal
but a note on sleaving down the piercing needle hole. You may see good improvements, but I'd bet that the needle would start working as a piston, driven by cartridge pressure, closing the valve faster. Good, but maybe inconsistent.

My philosophy is to make everything pretty wide open, then reduce dwell and lift until I get as low a velocity as I want. Making the charge navigate restricted ports seems wasteful to me.Some of your charge is still struggling to get thru the port after the pellet is well up the barrel.

Ultralight strikers may not fully pierce a tough cartridge, that may be why factory issue tends to be so heavy.
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Joined: June 7th, 2010, 12:14 am

August 4th, 2010, 3:59 pm #10

The geometry of the area around the the neck of 12g carts and the piercing pin may have considerable effect on the "reservoir" effect of the entire CO2 tube. Piercing and sealing effects are all to be considered. I have no doubt that the conditions of equilibrium within and external to the cart it's self has a bearing on any scheme to control gas flow. At this moment, thoughts run through wondering how the addition of a sealing device (o-ring perhaps) on the strike pin that would isolate the valve body volume during shot cycle might offer a degree of control to the total gas charge available.
Bulk fill condition may be more easily contemplated.

An R&D valve is on order awaiting ..... with free delivery

I am sure others have gone before on such mumblings, but I have not come across their notes.
Last edited by CalG on August 4th, 2010, 4:00 pm, edited 1 time in total.
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