Valve dimensions
Hello,
I think I will make myself a “temporary” valve without regulator yet (just to lear more about the important factors in it).
Could someone help me out with few details:
1) In my standard Talon the exhaust bore diameter on valvestem is 2.5mm. That provides 29fpe. Are there any experiences for the size and length of that bore? I am aiming for 40 maybe 50 fpe. More is just waste of shotcount in my case. Is 4mm bore and 40mm length enaugh for that?
I try to maintain some length in valvestem to provide better and more consistent axial slide surface.
2) I have seen few valvebodies made from brass. I assume it is suitable material and strong enaugh to use?
3) What force is in the standard talon and condor valve spring?
4) What material is the sealing of valve stem? Delrin? PTFE? POM?
5) Should the sealing from surface be conical at 45 degree and also the surface it seals? Or should there be an edge against conical sealing surface?
6) Has anyone used delrin or other plastic sliding surface for valvestem instead of brass?
Here’s quick sketch of the idea. Not even nearly ready yet. Many things missing but I hope this explains where I am aiming.
Red is delrin or pom. The long slide is pressfitted and inner hole finetuned after fitting for precise slide tolerance. Maybe will add O-ring to front. I wish to leave some spare room for valvestem bore to make it bigger later if necessary. It’s now 4mm. Side bores are 3.5 mm (3 times at 120 degree angles). End of valvestem goes directly to breech like in many latest designs (Thanks to Marc 😉
Thanks.
-Mike
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Viewing 8 replies - 1 through 8 (of 8 total)
Pictures of a valve stem. This one is brass, I no longer use brass — too weak. Notice how “wide open” the air passages are. Streamline all edges, it makes a BIG difference in power.
Notice the rubberized abrasive dremmel points.
Mark
I learn a lot reading about you guys working on your valves. Keep it up because one day I am going to have to give it a shot.
Great info! Thnx
I have not tried to line the valve bore with plastic.
A steel valve stem sliding in a brass bore works very well.
I tried adding an “O” ring on the stem, it just added resistance and killed the power.
When I build my valve stems, I make it taper by a few thousandths. That is, the breach end of the stem has .001 clearance in the bore, so not much air gets past. The other end of the stem has .004 clearance in the bore. This allows enough “slop” for the plastic seat to center up in the orfice — makes it seal up with no leaks.
Mark
oh i forgot:
A tapered angle on your plastic seat makes for good power adjustability.
A flat seat makes a little more power, but you cant adjust the power with the power wheel.
I cut a 60 degree seat into the brass with a center drill (very shallow- not too deep), and use a 55 degree angle on the Derlun. Then polish the brass seat area with the rubberized abrasive dremmel point.
Mark
Mike:
The valve stem diameter is very important. The valve stem Acts like a piston in an air cylinder. The force from this piston action works to close the valve. The larger the valve stem diameeter the greater the piston closing force is. This piston force pushes the hammer back to close the valve.
I used a .375 diameter valve stem on my first valves. This produced a valve that made about 35 to 40 FPE. What was interesting was that increasing the barrel length from 18 to 24 inches actualy produced less power. This told me that the valve was not staying open long enough to keep pushing the pellet down the last 6 inches of the barrel. The next valve I built had a .312 inche diameter valve stem. The power went up to the 50 to 60 FPE range, even though the hole through the valve stem got smaller. What was happening was that the valve was staying open longer. The piston action (the force that closes the valve) is decreased With the smaller valve stem diameter, allowing the valve to stay open longer.
When you build your valve, make the narrow area between the high pressure side and the low pressure side as short as you can — this helps with power.
I used a 60 degree taper in the low pressure side of the orface. Also any steps or irregulaties in the transition from the taper to the valvestem bore will really kill the power.
A good orface size is .173 inch when using a stock talon hammer and spring. .200 is too big to open with a stock talon hammer and spring.
Delrun works good for the seat. To get a good seal (no leaks) the first time and every time — get a rubberized abrasive point for your dremmel tool. Polish the brass valve seat area using the rubberized abrasive dremmel point. Seals with no leaks the first time.
Streamlining the passages where the air enters the valve stem makes a HUGE difference. Work your design to minimize any frontal area on your valve stem, where the air enters the valve stem.
Look at my other posts, I have pictures.
Mark
45 degrees on 45 degrees works fine when done well. I always use a 120 degree seal(same angle as a steel drill)(so less steep as a 45 degree sealing surface) I cut the bore where the stem rides in and the valveseat face in one go using the lathe. The I cut the delrin part and cut the bore and the seating face also in one go. Always use a interference fit between stem and delrin. Put the valve together and with some polishing paste I lap the delrin and brass together using a battery operated drill. Take apart, wash with washing up detergent. dry thuroughly and lube with a little bit of silicone grease. Now if you pull on the stem and twist it between your fingers so that the delrin “seals” on the brass and you feel more and less resistence periodically as you twist it. That means your seat and delrin are missaligned. Lap some more. In alle the valves I have made I had just 2 where I had to redo something.
hope this helps. Regards,
Marc
I try to maintain some length in valvestem to provide better and more consistent axial slide surface.
2) I have seen few valvebodies made from brass. I assume it is suitable material and strong enaugh to use?
3) What force is in the standard talon and condor valve spring?
4) What material is the sealing of valve stem? Delrin? PTFE? POM?
5) Should the sealing from surface be conical at 45 degree and also the surface it seals? Or should there be an edge against conical sealing surface?
6) Has anyone used delrin or other plastic sliding surface for valvestem instead of brass?
1) Cant help much with this, All I know is that the bigger the hole in the middle the more power people get.
2) Brass is fine using the stock valve design. You’d have to model your own design to make sure its properties meet some level of safety margin.
3) I havent measured mine, I always took them apart and just set them to be at the point where the spring just starts to depress. But I vaguely remember 8lb’s being thrown around as a number.
4) Delrin
5) the seal is 45 degree or there abouts. Judging by the wear on mine there is a 90 degree lip that hits the 45 degree seal cutting into it. I cant comment on whetehrer a 45 to 45 (basically a flat surface) seal would work or not.
6) the older valves had steel valve bodies without a brass insert and steel stems. New valves use a brass insert and steel stem…. In the past I used brass tube in a brass body and didnt notice any difference.
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Thanks Guys! That’s awesome help.