My First QB Valve Mod !

[wll2506]

I know now what to do, and it will be a little different from this first one but not much.

All I'm doing is cutting off .550 from the back, a groove on the tube, a conical spring and a grind down on the back of the poppet  to about .225. The poppet moves nice and smooth ;-  ) I'm hoping for an increase of 30-40 fps with this valve mod, hope I get more.



wll

[BigTinBoat]

I know now what to do, and it will be a little different from this first one but not much.

All I'm doing is cutting off .550 from the back, a groove on the tube, a conical spring and a grind down on the back of the poppet  to about .225. The poppet moves nice and smooth ;-  ) I'm hoping for an increase of 30-40 fps with this valve mod, hope I get more.



wll

A "groove on the tube"? what's that? Please don't tell us you are going to cut a groove in the air cylinder to hold the spring.

[wll2506]

I know now what to do, and it will be a little different from this first one but not much.

All I'm doing is cutting off .550 from the back, a groove on the tube, a conical spring and a grind down on the back of the poppet  to about .225. The poppet moves nice and smooth ;-  ) I'm hoping for an increase of 30-40 fps with this valve mod, hope I get more.



wll

No, what I meant is the grove I put in the next valve will be not as wide as this one, being the the back end is opened up and the conical spring leaves wide open air flow as there is no washer or ? to block the air.

wll

[Gippeto]

On the next one remove most of the aluminum...only need a ring to help hold the o-ring in place. Don't need a valve spring either...add an e clip or o-ring in a groove on the valve stem to keep it from falling completely out. Valve spring contributes very little force compared to that derived from the pressure.







Al

[YEMX]

Please, more detail!!

[BigTinBoat]

No, what I meant is the grove I put in the next valve will be not as wide as this one, being the the back end is opened up and the conical spring leaves wide open air flow as there is no washer or ? to block the air.

wll

OK, I would say take more out. The more metal you can remove the more space that is available to store "on-board" (regulated) air for your shot.

[wll2506]

On the next one remove most of the aluminum...only need a ring to help hold the o-ring in place. Don't need a valve spring either...add an e clip or o-ring in a groove on the valve stem to keep it from falling completely out. Valve spring contributes very little force compared to that derived from the pressure.







Al

So I don't need ANY spring at all !! how does that work ?

wll

[Buldawg76]

The high pressure air in the tube returns the poppet to its seat so just need a c clip or oring on the end of poppet stem behind the valve block to prevent the poppet from coming fully out of the valve if/ when air pressure is removed from tube as in servicing.

Gippeto can tell us how far the c clip or o ring groove needs to be back from valve block on poppet stem hopefully.

Gippeto, Inquiring minds want to know ?

Mike

[nervoustrigger]

The spring vs. no spring thing is what we were talking about in the current "Velocity vs barrel length in QB" thread http://www.gatewaytoairguns.org/GTA/index.php?topic=104460.0

As mentioned there, it's a dicey proposition to run no spring if you are a pump filler since you may not be able to build pressure fast enough to get the poppet to seal. 

Also, if it were an unregulated rifle, having no spring tends to yield a narrower useful bell curve because the restorative force to close the valve is directly proportional to the pressure in the tube so it doesn't self regulate the lift vs dwell as well.  Just something to keep in mind.

[Buldawg76]

The spring vs. no spring thing is what we were talking about in the current "Velocity vs barrel length in QB" thread http://www.gatewaytoairguns.org/GTA/index.php?topic=104460.0

As mentioned there, it's a dicey proposition to run no spring if you are a pump filler since you may not be able to build pressure fast enough to get the poppet to seal. 

Also, if it were an unregulated rifle, having no spring tends to yield a narrower useful bell curve because the restorative force to close the valve is directly proportional to the pressure in the tube so it doesn't self regulate the lift vs dwell as well.  Just something to keep in mind.

Yea most definitely really only a mod for an HPA regulated gun.

Mike

[wll2506]

My next mod in line if my first did not work was Jason's ..... But if I don't need any spring at all and it does not effect anything, well that makes a new ball game.

I can use a very small eclip that would not pass through the valve and be done......why aren't others using this method instead of cutting out the back end of the valve with all kinds of springs and all kinds of  %#]*

wll

[Gippeto]

Gippeto can tell us how far the c clip or o ring groove needs to be back from valve block on poppet stem hopefully.

Stock Qb is setup where the striker will hit the valve retention block when valve stem has moved ~ 1/8"...keep a bit more than that much travel. Could simply epoxy a piece of brass tubing onto the stem once installed in the valve body...easier than making a groove and doesn't weaken the stem. A bit of heat will loosen the epoxy should removal be necessary...at which point the valve stem is likely toast anyways.

As I said...valve spring contributes very little to the forces...calc them out if you like. MOST of the force is already coming from the pressure.

Tune the dwell by adjusting striker mass and poppet stem diameter. Can adjust required opening force by altering sealing diameter at the "hat" part of the valve stem too. Everything has a cause and an effect...change parameters to cause expected/desired results.

Admittedly a great deal easier to fine tune if one has machine tools.

As far as pump guys go....delrin perimeter sealing valve stem on a flat faced valve body straight off the lathe, no lapping....seals @100psi from the shop compressor. That would be the Gen 2 valve in the first pic.

Qb stem with it's soft urethane seal...should be no issue getting it to seal. JMO.

... force to close the valve is directly proportional to the pressure in the tube...

That IS self regulation.

Al

[wll2506]

Gippeto can tell us how far the c clip or o ring groove needs to be back from valve block on poppet stem hopefully.

Stock Qb is setup where the striker will hit the valve retention block when valve stem has moved ~ 1/8"...keep a bit more than that much travel. Could simply epoxy a piece of brass tubing onto the stem once installed in the valve body...easier than making a groove and doesn't weaken the stem. A bit of heat will loosen the epoxy should removal be necessary...at which point the valve stem is likely toast anyways.

As I said...valve spring contributes very little to the forces...calc them out if you like. MOST of the force is already coming from the pressure.

Tune the dwell by adjusting striker mass and poppet stem diameter. Can adjust required opening force by altering sealing diameter at the "hat" part of the valve stem too. Everything has a cause and an effect...change parameters to cause expected/desired results.

Admittedly a great deal easier to fine tune if one has machine tools.

As far as pump guys go....delrin perimeter sealing valve stem on a flat faced valve body straight off the lathe, no lapping....seals @100psi from the shop compressor. That would be the Gen 2 valve in the first pic.

Qb stem with it's soft urethane seal...should be no issue getting it to seal. JMO.

... force to close the valve is directly proportional to the pressure in the tube...

That IS self regulation.

Al

So in effect a small piece of shrink tubing would work because it would never come in contact with anything and it is there just to stop the poppet from falling out of the valve ? Am I correct ?

wll

[pllagunos]

On the next one remove most of the aluminum...only need a ring to help hold the o-ring in place. Don't need a valve spring either...add an e clip or o-ring in a groove on the valve stem to keep it from falling completely out. Valve spring contributes very little force compared to that derived from the pressure.







Al

Gippeto, the valve you show is custom made right? If I wanted to do the same with a standard valve, it would basically be to remove the aluminum and leave a ring to hold the o-ring, and remove the spring?

[rsterne]

While you can run a PCP without a valve spring, and in a regulated PCP I see no real problem in doing so.... in an unregulated PCP, the spring does increase the pressure range of the bell curve to some degree.... The main closing force on the open valve is the pressure times the area of the valve STEM.... In a QB, that stem is 3mm (0.118"), so at 1500 psi the closing force is only ~16 lbs.... The valve spring is typically about 5-7 lbs. so is actually a reasonable percentage of the closing force.... The force holding the poppet against the seat when the valve is closed, however, is MUCH higher.... If the seat is 1/4" diameter, at 1500 psi it is 74 lbs., so the spring is less than 10% of the total....

Bob

[SpiralGroove]

Hey Jason,
Assuming when you reversed the spring & used e-clip, it necessitated drilling the "pre-valve, steel piece" that partially covers the stem (to accommodate the larger clip/spring)?  Hole between 1/8" and 1/4" 

Right?

[Gippeto]

wll...correct...and even simpler.

pllagunos...The valves are custom made. What you suggest would be the closest approximation one could do with modifying the stock valve.

Bob...quite true. I do use 3/16" for valve stems....benefits of machine tools. Creative person working carefully could mod the stock valve to such using only a drill press and a few odd bits to make a jig.

Al

[nervoustrigger]

That IS self regulation.

You're right.  The point I was trying to make is that the self regulation works better with a valve spring present.

Assuming when you reversed the spring & used e-clip, it necessitated drilling the "pre-valve, steel piece" that partially covers the stem (to accommodate the larger clip/spring)?  Hole between 1/8" and 1/4" 

Kirk, it will be close.  Mine cleared but you might need to open it up just a hair to ensure it cannot drag.

[SpiralGroove]

Hey Jason,
Thank you Sir