Hammer spring/valve spring... Questions?

Its going to be a bit noobish to start but ehre it goes...

First off, what are they? (i think I know but would like clarification)
And for the second question. I have read of people shimming them or installing lighter springs. What are the advantages/disadvantages of doing this?




Im shure ill have more but for now this is all.






Jason

[ribbonstone]

Are two coiled springs at work.  One is inside the valve (valve spring), and it has a two-part job.  One job is to retract the piercing stem ( the pointed metal part that puts a chole in the CO2 cartridge), the other is to supply spring pressure agains the valve to keep it closed. (Will ignore the CO2 pressure for the time being.)

The other coil spring is behind a moving cylinderical hammer (hammer spring)...it's the spring you put under tenstion as you open and close the bolt.  It's job is to supply the force to the hammer...which strikes the stem of the valve (being held sut by the valve spring) and forcing it open for a fraction of a second.

IF you were to use a lighter valve spring, the hammer would knock it open for a bit longer....if you used a heavier hammer spring (or increased the tesnion of the current spring by using spacers) the hammer would strike the valve stem harder...and open the valve for a little longer.  Many modifided guns tend to not seal at all unless the gun is quickly recocked after popping a new cartridge...hammer spring force is so much greater than valve spring force, the gas tends to squirt out in a long hissssss.  Cocking the gun lets the valve spring close the valve and build up normal co2 pressure...usually that pressure is enough to close the valve when firing.

They have to be somewhat in balance.  Excess gas released after the pellet has moved well down the barrel doesn't add much (if any) vel.

Noise is NOT  a great indicator of pellet speed...is an indication of wasting gas.

Spring loaded metal hammer to spring loaded metal valve stem does promote some bouncing...and those bounces can be wasting gas that doesn't go into producing more vel.

[DanoInTx]

The wheels on the bus go 'round and 'round, 'round and 'round.  

Sorry, the explanation reminds me of "the hip bone connects to the leg bone".  You explanation is perfect though, forget I was ever here in fact:)

Dan

[ribbonstone]

On a QB recently worked on, got it almost right. Played a bit with the springs a bit.

Got the rifle to not leak when teh hammer was down and I pierced only one co2 cylinder.  On a guess, it took some time for that single cyilder to build up pressre in all that dead air space...and a slow increase in pressure isn't as good at sealing valves as a sudden rapid increase.  Uncocked, it didn't leak at all if 2 cartridges were used...with just one, would have a sharp,  but rapidly declining barrel hiss.  

Had done a simple valve mod, deburred and polished the internal parts, aligned the vlave, a bolt probe, etc. as well as the above spring foolishness. That all turned out to be hotter that I wanted (690fps)...substitued a factory valve spring and lightened the hammer spring a little bit....tested (650fps)...lightened the hammer spring a little more...and had it running at the vel.  wanted (620fps).  

Not noticing much differnce in shot count from out-the-box ...just cleaned of grease/preservative (575fps) but i'm real picky about accuracy.  If I notice a definate drop in trajectory, it will still shoot...and shoot well enough for plinking...but I tend to just fire off the decreasing gas goofing off rather than try to get anything serious done.

[DanoInTx]

If you pull the bolt open, then load one empty powerlet first, then a full one second, twist cap, unscrew 1/4 turn...hiiiissssss....but shouldn't leak from the exhaust valve even with hot springs.   That is "shouldn't" as in "Sounds right to me at least"....hehe!!!

Maybe Mike or Ian will chime in here?

Dan

Thanks for the replys and feedback. It has defenatly helped out alot.
What is the main reason to mod eighter of those springs or shim them?

[ribbonstone]

Power is the reason.  At least the illusion of more velocity if they are checking by how  loud the gun sounds but not chronographing.  May not be a significant rise in vel. past a certain point...but can make it a whole lot louder.  Gas NOT being used to push the pellet will make a nice loud crack, but add little if any pellet speed.