QB Valve travel observations

QB Valve travel observations

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

August 12th, 2010, 12:52 am #1

Just out in the shop having a look at the QB exhaust valve.

Interestingly, the valve stem protrudes through the Inside plug (0200) by .148 in. Seemingly, that would define a possible valve stroke amplitude of the same dimension, with any inertia travel added on.
Once a 12 gm cart (open and spent) is pressed up to the valve body gas entrance the piercing pin stops hard against the cart after only .084 in. of valve stem movement. ONLY 56% of the unrestricted possible movement.

Opening travel and duration may be significantly greater for valves modified to remove the piercing pin.

A second observation: That valve stem must have quite a life being hammered between striker and cart rather than a progressive slowing after being struck open by the action of spring and gas pressure I would expect a significantly shorter open duration.

A significant "tuning" aspect for opening and duration could be the length of the valve head/piercing pin combination. Even with standard springs.
For those retaining cart use any way.

Note that this is a single sample of parts. mfg. tolerance may show alternate numbers, but I believe the trend remains.



Cal
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Joined: October 25th, 2002, 3:46 pm

August 12th, 2010, 12:58 am #2

I rather doubt the valve stroke is limited by the hit on the powerlet while there is gas available.
Be worth looking over a powerlet out of a gun and see if it is peened at all.
interesting idea...
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Joined: November 17th, 2006, 3:51 am

August 12th, 2010, 1:13 am #3

..won't shoot nearly as long on one (less than 1/2 as many full power shots as when shooting 2 x 12gr).

Can drill and empty's neck to as large a diameter as possible, use that drilled empty as the bottom 12gr., load a full on as the top 12gr., and test the vel. Larger opening does seem to offer a little more travel. Of coruse, we're use to the idea of bulk fill giving more vel. than 12gr., and that valve stem travel just might be the main reason.


Crosman used a system like that on their low vel. Challenger 2000 (the 12gr. rifle). the valve stem is interchangeable with a standard 22XX valve stem, but the challenger has a longer brass shank... and that brass shank limits the valve's stroke. It's how they can honestly get 70-80 shots from one 12gr. (they're sub 500fps shots, but that's still a very stingy use of co2).
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Last edited by gubb33ps on August 12th, 2010, 1:15 am, edited 1 time in total.
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Joined: June 7th, 2010, 12:14 am

August 12th, 2010, 1:15 am #4

I rather doubt the valve stroke is limited by the hit on the powerlet while there is gas available.
Be worth looking over a powerlet out of a gun and see if it is peened at all.
interesting idea...
On the few carts I've looked at, the end butted to the valve shows multiple strike marks. But that could as well come from the last few shots when the pressure is failing.

I wonder what a "typical" valve opening is? So many conditions.
Light striker, heavy spring, la dee da de dah...
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Joined: October 25th, 2002, 3:46 pm

August 12th, 2010, 1:20 am #5

measure the squish.

I'll see if that will work
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Joined: March 28th, 2002, 6:54 pm

August 12th, 2010, 4:50 am #6

I suspect you'll find not much more that one stem diameter of travel(at least until gas pressure drops below normal)
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Joined: June 7th, 2010, 12:14 am

August 12th, 2010, 3:00 pm #7

Is between the valve body and the striker.

A plastic thickness indicator would go on that surface rather than the valve

Stem diameter is about .115 in.
Last edited by CalG on August 12th, 2010, 3:35 pm, edited 1 time in total.
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Joined: March 28th, 2002, 6:54 pm

August 13th, 2010, 3:57 am #8

I forgot the ring in the QB
Last edited by classicalgas on August 13th, 2010, 3:58 am, edited 1 time in total.
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Joined: June 7th, 2010, 12:14 am

August 13th, 2010, 4:49 pm #9

Just out in the shop having a look at the QB exhaust valve.

Interestingly, the valve stem protrudes through the Inside plug (0200) by .148 in. Seemingly, that would define a possible valve stroke amplitude of the same dimension, with any inertia travel added on.
Once a 12 gm cart (open and spent) is pressed up to the valve body gas entrance the piercing pin stops hard against the cart after only .084 in. of valve stem movement. ONLY 56% of the unrestricted possible movement.

Opening travel and duration may be significantly greater for valves modified to remove the piercing pin.

A second observation: That valve stem must have quite a life being hammered between striker and cart rather than a progressive slowing after being struck open by the action of spring and gas pressure I would expect a significantly shorter open duration.

A significant "tuning" aspect for opening and duration could be the length of the valve head/piercing pin combination. Even with standard springs.
For those retaining cart use any way.

Note that this is a single sample of parts. mfg. tolerance may show alternate numbers, but I believe the trend remains.



Cal
This from 2007

http://www.network54.com/Forum/113813/t ... tle+faster.



It's hard to get the search string just right to find the topic of interest.
I've just been scrolling the pages.

"To learn new, read an old book."
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Joined: March 3rd, 2005, 1:38 pm

August 13th, 2010, 11:10 pm #10

Just out in the shop having a look at the QB exhaust valve.

Interestingly, the valve stem protrudes through the Inside plug (0200) by .148 in. Seemingly, that would define a possible valve stroke amplitude of the same dimension, with any inertia travel added on.
Once a 12 gm cart (open and spent) is pressed up to the valve body gas entrance the piercing pin stops hard against the cart after only .084 in. of valve stem movement. ONLY 56% of the unrestricted possible movement.

Opening travel and duration may be significantly greater for valves modified to remove the piercing pin.

A second observation: That valve stem must have quite a life being hammered between striker and cart rather than a progressive slowing after being struck open by the action of spring and gas pressure I would expect a significantly shorter open duration.

A significant "tuning" aspect for opening and duration could be the length of the valve head/piercing pin combination. Even with standard springs.
For those retaining cart use any way.

Note that this is a single sample of parts. mfg. tolerance may show alternate numbers, but I believe the trend remains.



Cal
You will find you can remove some from the block and get more if you want it, the pin doesn't get to the end of the slot. A probe type pin will also give more travel, just what I have found may not be the right way but it works....adding resistance in the vavle gives more shots per fill and with other mods will keep the velocity up. it's not rocket science, just depends on how anal you want to get....

mailto:flyingdragonairrifles@hotmail.comhttp://www.airgunartisans.com/flyingdragon/
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