Lloyd Sikes was also involved in the latest development in the design of balanced valves for PCP airguns. Travis Whitney gave Lloyd the concept as a “back of the napkin sketch”, and Lloyd did the prototype work. Travis then continued the development, and I was privileged with enough “inside information” to allow me to build my own version. Thank you both for that opportunity!This aftermarket valve is made commercially by Jefferson State Air Rifles, and sold as the “SS Valve”, in varieties to fit many existing PCPs. It looks quite different, but functions much the same.When closed, the forces on the large diameter section of the poppet cancel out. The pressure P in the middle chamber of the poppet is atmospheric, so the force holding the valve closed comes from the small diameter portion of the poppet, (0.206 x 0.206 x PI/4) x 3000 = 100 lbs. just like in the other balanced valves above.Remember, these are “fake” dimensions, chosen for consistency in this article.When the valve is wide open, the pressure in the small chamber between the two poppet O-rings rises like the pressure P in the exhaust port to nearly 3000 psi. This cancels out all the forces except that 37 lbs. closing force on the valve stem area, and the valve cycles like a conventional PCP valve. Well, almost!Travis has added a little twist, allowing the SS Valve to be “fine-tuned”. He uses replaceable jets from Mikuni carburettors to control the diameter of the vent on the inlet side of the HPA poppet chamber.In my versions I use quite a large hole, about 1/16-inch diameter, because I am using my SS valves in big bores where I am primarily interested in easier opening to allow a lighter hammer strike. Travis has shown that by restricting the size of that inlet port, you can decrease the valve dwell, because that chamber acts like an air spring.Truthfully, I don’t fully understand this “jetting” system, but it sure seems to work!I can tell you that the diameter of the vent through the poppet is, once again, quite critical. If it is too large, the pressure between the poppet O-rings rises so rapidly, before the poppet has the chance to clear the seat by more than a few thou, the closing force rises and slams the valve shut, and you lose the ability to get that nice light hammer strike.It still works, you just have to hit it harder…On the other hand, if that vent is too small, the valve tends to blow open, like a spool valve, and it gets hard to tune. It has a definite “cycle” (like a Cothran Valve), and tiny changes in hammer strike can make it “work” or “not”.Once you get that vent about the right size, the valve can be tuned over a decent range of velocity with just hammer strike, and can develop a normal “bell-curve” in unregulated PCPs, but much easier to knock open. It also works great in regulated PCPs.
A couple days ago looking through my pellet supply I decided to try turning the gun all the way up and put some 23 grain magnum hunters over the chrony. The new side lever breech does cover up most of the #5 mark but it's on there. I was looking real close through my Optivisor and could see parts of the 5. This will be the next gun that comes apart, on the .25 the hammer spring did need some deburring on both ends and I think that it did make a difference comparing before and after. I'm also curious how big the ports are. The port that was on the .25 was very small, it's now 3/16". I made a TP from delrin for it that works great.I started with 3K and ended at 1.8K pressure.
I wonder how well a JSAR Balanced valve would work with the Xisico Sentry? (With and without porting)P.S. Here are Wayne52's impressive Xisico Sentry .22 results (stock gun using 23 grain pellets):https://www.gatewaytoairguns.org/GTA/index.php?topic=169145.msg155926879#msg155926879Quote from: Wayne52 on April 01, 2020, 03:59:05 AMA couple days ago looking through my pellet supply I decided to try turning the gun all the way up and put some 23 grain magnum hunters over the chrony. The new side lever breech does cover up most of the #5 mark but it's on there. I was looking real close through my Optivisor and could see parts of the 5. This will be the next gun that comes apart, on the .25 the hammer spring did need some deburring on both ends and I think that it did make a difference comparing before and after. I'm also curious how big the ports are. The port that was on the .25 was very small, it's now 3/16". I made a TP from delrin for it that works great.I started with 3K and ended at 1.8K pressure.
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