TUNING MY SELPHB VALVE…

Well I’ve had my Selphb valve for a few days now, and have tried to tune it to various pellets.
First off, I’ve had to put the selphb stem into a blod valve body as the selphb valve body is too small for the top hat 🙄 but the results should be on a par with an all selphb valve.
Now selphbs tophat is a little shorter than a blod, so the locking inset cannot go down inside as far as it should. To set the tp where it should be(remember, with a FLATFACED BREECH) I have had to set the locking inset right here……. 😯

As long as I’m careful when closing the breech, the oring should be ok. I’ve also smoothed the edges to reduce wear….
So tp is in the right place now.
I’m pretty sure that this selphb stem delivers more air than the blod stem does. The selphb stem has 4 small ports in the bottom compared to blods 2 or 3 big ports. Also, on blods stem, the ports are much higher up than on selphb’s. This means when the valve is opened, the seal lifts and selphb ports are exposed directly into the bottle. On blods, when the valve is opened the seal lifts and the ports are exposed up inside the valve body. This is clearly slowing down the air transfer in comparison to selphbs stem. Using the same hammer, preload and psi, the selphb stem is putting the same pellet about 75 fps quicker 😯

First pellet to tune is the JSB 18 grain. Im’ using an 18″ barrel. I’ll spare you the details. End result is I can’t slow them down enough!! With my lightest hammer of 50 grams, as little preload as I can, and playing around with various fill pressures, I couldn’t keep them from ss whilst trying to get a decent string!! I need a hammer at about 35-40 grams.

Next pellet to tune was the Eunjin. Good snug fit in the barrel.
2600 psi 50 gram hammer, 68mm hammer+spacer preload.
949 941 943 971 939 938 939 962 937 927 931 922 917
948 912 913 949 902 892
Not bad, bit more work and I could tighten that up, valve allowing. BUT, they shoot for shit. Put a good 100 or so through the barrel, and they did tighten up a little, but not enough.

Back to the good ol’ Kodiak (I buy them here as Bisley Magnums, same pellet)

2500 psi fill, 50 gram hammer, 70mm hammer+spacer preload.
980 1009 1004 1009 1009 1017 1009 1018 1009 1009 1008
1009 1014 1000 1003 1001 1000 998 994 994 😯 😯

Drop that first shot and thats a very respectable 20 string!! Notice how many 1009 shots there were?!.

Conclusion so far? If the valve actually worked as delivered, there was no weakness in the stem etc, I’d be a very happy bunny.
I’m just about to do another string on the Klods using the same settings. Lets see how it compares to that last string…. I’ll post up the 2nd resul;ts.