Optimum Set Pressure (regulated)

[Rabbitstopper]

Evening all,

What would be the optimal set pressure for a given tune?

Let's say ( strictly as examples) an aim of 20fpe with a 20cc plenum.

850psi maxed out preload making the 20fpe,

1200psi in the middle or,

1800 psi just talking a sip.

I'll include and ssg on all the above.  I am wondering about consistency more than anything, I have also read that if there is not enough of a pressure drop per cycle the reg refresh rate for want of a better word can be affected.
Thanks,

[rsterne]

The pressure should be enough to produce the 850 fps before you install the regulator, plus maybe 5%.... You want to tune to the "knee" of the curve for best consistency.... Read the thread about tuning a Regulated PCP....

https://www.gatewaytoairguns.org/GTA/index.php?topic=74919.0

Bob

[Rabbitstopper]

Awesome thanks, so tune with a pressure just enough and a little extra for the knee. The downslope especially for sub 12 fpe countries is definitely a no when we are aiming for an 11.5 fpe tune could well put you over when off reg.


Again,

Thanks.

[rsterne]

Absolutely, and the same thing would be a problem if you are shooting FT with a FPE limit.... off reg. and you're over.... You want about 5-10% more pressure than gets you the velocity you want when unregulated, to allow for detuning on the knee, and the effect of the plenum volume....

Bob

[Rabbitstopper]

Thanks for the post it was a good informative read.

I have just been reading Motorhead's advanced tuning guide. My understanding is to find a spring with a rate that will reach a desired fpe and no more.
There becomes a point when the force on the poppet due to pressure cannot be over come without adding preload or a spring with a higher rate. When at this point the fpe will begin to drop until eventually the increasing pressure causes valve lock.I think I have this aspect correct? However!

Let's say for example sake goal is 11.5fpe, so find a spring which can develop 12fpe then de tune to the knee (this is my goal but I will have to do the math). The part which has phased is the first paragraph where motor head says ''reduce hammer pre-load some". If I found a spring which produces my 12fpe goal @1200psi I'm still not on the plateu as I can add preload increasing dwell.

However again! If using this spring with reduced preload and I went to 1300psi and fpe dropped some would this be the same end? I have got my head stuck in the mind set that the approach would be to use a spring with max pre-load to reach the 12fpe? I have probably missed something simple, sorry for the long post,

Thanks,

David.

[rsterne]

While you don't want too heavy a hammer spring, I always like to have a spring that will allow you to find the plateau at the setpoint pressure you are using.... Otherwise, you won't know where the knee is, and if you have to increase or decrease your setpoint.... If you are using an SSG, you have two adjustments, one for preload (on the guide) and the other for the gap between the hammer and the valve stem when the gun is uncocked…. This will give you more flexibility in your choice of spring....

Bob