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.
All Replies
First post so try to be gentle!
I am interested in getting a modified high flow valve for my stealth. Who currently makes them? and which one do you recommend i get?. I have seen a post on here that says Blodnob no longer makes them and these selph valves seem to have some issues.
UK supplier would be preferred
Thanks
Hi guys,
First post so try to be gentle!
I am interested in getting a modified high flow valve for my stealth. Who currently makes them? and which one do you recommend i get?. I have seen a post on here that says Blodnob no longer makes them and these selph valves seem to have some issues.
UK supplier would be preferred
Thanks
Thanks pabs, i get it now. spring is external to seal. so broken stem…. no spring…. pressure to pop it clear then depressure.
sorry got mixed up….
The other cause could be the valve not concentric with a good seal that requires a high differential pressure to ‘make’ it seal.
You had me going back there when you say that you can slowly depressure a tank by filling then cracking the bleed. That should not be possible with an airforce type valve. .
To clarify- It would fill to required pressure. Then, when I try to depressure by the bleed valve so I can remove the bottle, all the air would come out via bleed . The tophat becoming bound by the too tight oring.
I’m using the supplied tp return spring that is a fair bit stronger than the blod one, so that shouldn’t be an issue. The rate at which the air wants to come out would suggest its not a badly sealing seal. Just too much air.
I said to depressurise the bottle via the bleed if your selphb stem snaps.
Bring the bottle up to pressure to open seal on the end of the broken stem. Then close the tap and open the bleed slowly. The seal on the broken stem will not re-seal and you can get the air out in a safe and controlled manner.
if the valve spring is too light to overcome the oring friction then it will indeed leak on depressure. You said filling so I presumed you were putting air in as it bunched up.
The other cause could be the valve not concentric with a good seal that requires a high differential pressure to ‘make’ it seal.
You had me going back there when you say that you can slowly depressure a tank by filling then cracking the bleed. That should not be possible with an airforce type valve. It is actually a 100psid check valve and should seal immediately when filling stops.
Ok Mr Pedant 🙄 Yes, the tp fits in the valve body, but its so tight on the oring that when the valve is under pressure( when I’m filling the bottle) the already tight oring expands enough to lock the valve in the open position. So when I try to depressurize the line to take the bottle off, it all comes out again.
Pabs, how would that be possible as the pressure is all equalized on the TP oring when connected to the fill?
I am in agreement that a proper fit is required and there is no reason for a tight fit here, just a nice sliding fit is adequate to do the sealing on firing.
I have gone away from using an oring and use a Delrin split ring for this purpose. It is the least parasitic with an adequate seal.
Walter….
I would think that as I depressurize the line, that equalised pressure is no longer there, and the difference is sufficient to lock it open. Even when I tried to open the bleed extra quick, it would not seal and the air came out with much gusto. Using the same stem and tp in blods valve body, there were no problems, tp in the same position as before etc.
And apart from anything, there is nothing else to cause this.
That’s not quite correct. The SelphB tophat fits into the SelphB valve-body just fine but the o-ring locks up while trying to fill the bottle (and would probably do the same when firing and cause a dump).
Ok Mr Pedant 🙄 Yes, the tp fits in the valve body, but its so tight on the oring that when the valve is under pressure( when I’m filling the bottle) the already tight oring expands enough to lock the valve in the open position. So when I try to depressurize the line to take the bottle off, it all comes out again.
Pabs, how would that be possible as the pressure is all equalized on the TP oring when connected to the fill?
I am in agreement that a proper fit is required and there is no reason for a tight fit here, just a nice sliding fit is adequate to do the sealing on firing.
I have gone away from using an oring and use a Delrin split ring for this purpose. It is the least parasitic with an adequate seal.
Walter….
Because the selphb valve body was made too small to fit the tophat in. The oring is too tight on the tp and locks open when trying to fill.
That’s not quite correct. The SelphB tophat fits into the SelphB valve-body just fine but the o-ring locks up while trying to fill the bottle (and would probably do the same when firing and cause a dump).
Ok Mr Pedant 🙄 Yes, the tp fits in the valve body, but its so tight on the oring that when the valve is under pressure( when I’m filling the bottle) the already tight oring expands enough to lock the valve in the open position. So when I try to depressurize the line to take the bottle off, it all comes out again.
Because the selphb valve body was made too small to fit the tophat in. The oring is too tight on the tp and locks open when trying to fill.
That’s not quite correct. The SelphB tophat fits into the SelphB valve-body just fine but the o-ring locks up while trying to fill the bottle (and would probably do the same when firing and cause a dump).
Because the selphb valve body was made too small to fit the tophat in. The oring is too tight on the tp and locks open when trying to fill.
I used the Valve return spring that comes in the selphb valve, and I also used the main spring that comes supplied.
The strings look very impressived
“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.”
Pab, I don’t understand. Why not use the complete Selph valve?
Pab which spring did you use in the valve?
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Pab,
It looks to me like there are a couple design elements here that could be combined a couple ways to create a better mousetrap. Seems to me you could use one TP design with a flat faced breech and another with a traditional design and attach those to the port design of the Selph stem to get a high power output. Not that I’m interested in high power designs… 😀