That’s true…a lightweight hammer will require more hammer spring tension. If the cocking effort is already objectionable, that would be a step in the wrong direction. I’m just a little surprised that is the case for a .25 cal at ~60fpe, particularly with the mechanical advantage of a sidelever.
Regarding Broekzwan’s suggestion of using a weaker spring in the valve, that’s worth a try. It’s not so much about making the valve easier to knock open (lift) as it is about helping it to stay open longer (dwell).
To explain a bit, how hard it is to open the valve is mostly due the air pressure. Using a somewhat arbitrary example to illustrate what I mean…imagine we have a regulator setpoint of 2000psi, and let’s say the valve throat is 0.300” diameter (an area of 0.0706 sq in). The force holding the valve closed is 2000 * 0.0706 = 141lbs. Meanwhile a stiff valve spring is what, 10lbs tops? The spring represents but a tiny fraction of the force holding the valve closed, less than 7%.
However once the valve is knocked open, the spring plays a much bigger role in how quickly it will close. Let’s assume the valve stem is 3mm…the 2000psi acts against this 3mm to exert a closing force of 22lbs. Another 10lbs contributed by the valve spring is significant…an increase of almost 50%. So by using a different valve spring, we can influence the dwell time quite a bit. For example, using a weak spring can help offset the dwell that is otherwise lost by using a lightweight hammer.
Having said all that, I want to note that often times this “lost dwell” is precisely what I’m trying to achieve. With many AGs, there is too much to begin with and I’m interested in reducing it. But if the situation requires it, changing the valve spring is one way to do it. Also, I don’t like going too light because it helps with the self-regulation characteristics of the valve. By self-regulation I mean the valve’s ability to produce a stable velocity over a wide range of pressure like an unregulated PCP operating near the top of its bell curve. That characteristic is still very useful in a regulated PCP because no regulator is perfect.
While I was talking about the decrease in hammer spring tension I still had my Steyr in my mind. When a Steyr is set at a 16J / 12 ft/lbs setup about 1/3 to 1/2 of the force on the valve comes from the valve spring. It's a lot smaller valve so that makes sense.
Talking about the valvespring: a mistake a lot of companies make is give the valve a stiff spring with quite some pre-tension. Steyr for example has approximately 30N of pre-tension on the valve and every mm the valve is pushed back adds 10N to force pushing back (spring constant is ~10N/mm). The result is that the hammerspring needs quite some pre-tension for a low power airgun and combines that with some nice hammer bounce.
If you change the valve spring to one that has the length that it fits right in between a seated valve and the spring seat inside the plenum you take away the extra energy you need to open the valve (yes it might only be 1:15 ratio like you calculated but that's already 6.25% energy you don't need anymore. If you then put a super stiff spring behind the valve you can achieve super fast dwell times but the energy you release is limited or you need to slam that valve with excessive violence. Put a very light spring behind the valve and you can quite easily achieve high powers but low power becomes a problem there. This is where the art is, finding the right spring constant to achieve exactly what you need (there is no one valve spring that works for all cases
).
Look at a FX hammer, it weighs about 18 grams, compare that to the (give or take) 80 / 90 grams of a RAW hammer and both are able to achieve approximately the same muzzle energy This feels to me like trying to open a door with a truck instead of with your hands while needing a boat load of spring force to force that door back shut to only have it opened for a short time. I have a feeling that with a decent diet and properly calculated or empirically chosen components there is a lot to win in these RAWs without losing power. This isn't only for RAW by the way, there are more brands that don't really seem to get this
