I have been playing around with a long barrel carbine version of the Benjamin Marauder pistol.
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I wasn't happy with port changes and was surprised to see my results didn't seem to mirror the results I got on my standard pistol w/8"(IIRC) barrel. The short barrel version seemed to produce the same or more power than the long barrel all else being equal. I took the valve out and installed a spare I had with a .022 wire spring thinking it would move the bell curve to the higher pressure side and found out it not only didn't, it seemed to be less efficient.
I'm getting ready to install the original valve back in but took a minute to open it up and take a quick look and was surprised to see a .045 wire spring. This is .009 larger wire diameter than my other valve spring. I'm going to install a .036 which is the same size as the pistol and rerun my tests. I was really puzzled by my initial test results with the long barrel and I suspect the next tests will be more like what I suspected I should get.
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Strange to find two different sizes in these valves.
Generally, a lighter valve return spring will, all else equal, yield a valve that self regs better than a heavier spring, but flow more air at a given pressure. You can compensate with striker weight and travel, but those changes will shift the sweet spot pressure too.You may need to open up the valve to reservoir port to make the long barrel work
Generally, a lighter valve return spring will, all else equal, yield a valve that self regs better than a heavier spring, but flow more air at a given pressure. You can compensate with striker weight and travel, but those changes will shift the sweet spot pressure too.You may need to open up the valve to reservoir port to make the long barrel work
I considered changing the striker weight but it would be pretty difficult to make a decent custom striker considering the design. The valve port is .1 and I'm betting it has adequate flow. I achieved good efficiency with a .09 port and the OEM .045 wire valve return spring so I have another.01 if the .036 wire spring doesn't give me what I'm expecting. I've done all my testing with maximum striker travel.
If I'm still not happy I'll fire up the machine shop and start hacking on my spare.
PS The lighter valve return spring didn't yield any more power at higher reservoir pressures. I suspected the striker can't overcome the pressure regardless of the lighter valve return spring. It seemed to flow more air at lower pressures as you stated making the gun LESS efficient. The spring change did not increase power at high reservoir pressures and the total shot count was lower.
I'm not sure where the .036 wire spring originates. I was reviewing old pictures of my spare valve and I show its spring also measured .045 wire size. The .036 wire spring was in the parts box with the valve but the valve that came with the gun, and now it seems the spare valve both have .045 wire return springs.
I'm still going to try the .036 wire valve return spring but I'm not sure of its origin now. ?
" The lighter valve return spring didn't yield any more power at higher reservoir pressures. I suspected the striker can't overcome the pressure regardless of the lighter valve return spring." You're probably correct.
If you want to keep the higher fill pressure, you need more striker energy, or an easier to open valve (harder, less seat area)
With the small valve volume I suspect you have, flow between the reservoir (no regulator, correct?) and the valve, volume becomes a major factor, so that port needs to be several times as large as the barrel port. Otherwise the average pressure at the valve seat drops to a small faction of nominal pressure during the firing cycle. Low efficiency and low power relative to pressure is the result. A larger valve volume/plenum helps.
