Adjusting a SlephB valve
How do you? I bought one awhile back from a member here and didn’t get to try it ’til just a couple of days ago. I tried a few different setups with stock spring and 93g hammer, heavy spring and hammer and stock spring and 120g hammer….never got over 450fps with Jerry’s 9 ringer’s.
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Wok sent me a pm and told me to post my question in the forums because he doesn’t have or use Selph valves.
“finding the sweet spot” is the same on all air force rifles as RR just noted.
Wok sent me a pm and told me to post my question in the forums because he doesn’t have or use Selph valves.
Yup real good wright up in the Quick Reference forum.
Every valve is different, but heres what I did.
PW at a fairly low setting, TH gap around .050. Shoot over chrony a few shots, twist tophat out .002-.005. Shoot a few more over chrony.
Eventually you will find the gap where your velocity is highest and widening the gap does little to improve velocity. The goal is highest velocity with smallest gap, which is most efficient for that pellet. This is known as the “sweet spot”.
The principle is the same for a Selph-type valve, but the “gap” I speak of is actually a distance between valve body and shoulder of tophat. You’ll have to figure out how to measure that distance yourself.
Probably the best way is with a depth measurement function of a caliper.
Wok has a writeup somewhere here that explains it better than I do.
What exactly am I trying to accomplish? I guess I should ask, how will I know it is at its sweet spot?
Yup, if there’s no means of fixing it in place, you’ll want to loctite it once you get it where you want.( Which will require you to keep checking the setting between each shot until you find the sweet spot. That’ll be fun for you…. 🙁 )
After spending some time with a flashlight, I found out that all I have to do is “spin” the top hat off. There’s no grub screw or any type of screw for that matter, that holds it in place. There’s no place to put one either. Will it most likely back out while shooting?
Any idea what size the required allen key is? I’ve gone through every one I have and none fit.
Ive had the same prob i lock tite it going to mod the design extend the shaft cut for access same as the locking ring and wind the top hat all the way in and file both sides a small flat spot so can get a spanner17mm to adjust it all but lock tite is the answer bit of a faff but has to be done ill post pics of before and after to let u guys have an idea. Enjoy. Love u.
You can screw the tophat out. Loosen the locking grub inside the stem, then screw the tophat out to desired setting. Then screw down locking grub again. But be aware, the tophat can drift out after each shot. I made it part of my firing routine to check tophat hadn’t unscrewed itself a little. Of course, you can loctite the whole tophat once its set right.
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Yep adjustment is the same. Move tophat out = valve opens further. You will eventually hit the zone where moving it out no longer makes the pellets faster.
Oh and I used to have a Selph valve. Instead of tiny grub screws to hold the tophat in place, the tophat on a selph valve is supposed to have a slotted threaded ring that turns down against the top of the step to “Jam” it in place. This threaded ring is INSIDE the tophat. Finding a screwdriver that fits in there correctly is the biggest problem you will face.
Problem is, firing the valve causes the tophat to turn out which loosens the jam nut so thats why you need to locktite it.