Simplified Balanced Valve

[rsterne]

Well, Brian, you certainly contributed to this round of development.... It will be nice to see balanced valves work into the mainstream of airgunning…. I hope this thread has given that a push....

Bob

[oldpro]

 I can tell you this much we will be launching several guns this year and all will have the option of a balanced valve.

[mann]

Well I got the adjustable transfer port screw in it wasn't the easiest after I snapped a cheap 8/32 tapp off in it but I got it finally

[rsterne]

That looks like it will work....

Bob

[mann]

10/32 threw side of the valve like the original mrod valve and can adjust it threw the original hole in the air tube  . I need to pick up another to lock it down and some new screws for the breech to many times on and off being the gun I tinker with ever winter it seems like

[mann]

Well I got it tuned down to 815 fps before I couldn't get below 850 31 gram peek hammer  13 lb flat spring on ssg had to order some new breech screw other than that check it for leaks and it is down i hope

[Brian W Cook]

Staying on track with the balanced valve business.   Where do most of you get your peek at ?  Is $39 a foot for .750 the going rate ?
I’ve kinda been out of the fabricating airgun parts loop for about 5 years.   
All this has got me interested in retrofitting a piston to my .45 Lasso rifle .   It’s kinda maxed out on hammer weight and stroke and it’s limited to about 3100 psi.     
Would like to be able to run 35 or 3600

[PakProtector]

Staying on track with the balanced valve business.   Where do most of you get your peek at ?  Is $39 a foot for .750 the going rate ?
I’ve kinda been out of the fabricating airgun parts loop for about 5 years.   
All this has got me interested in retrofitting a piston to my .45 Lasso rifle .   It’s kinda maxed out on hammer weight and stroke and it’s limited to about 3100 psi.     
Would like to be able to run 35 or 3600

$33 here: https://drakeplastics.com/peek-rod/

but yes, it is a bit pricey...
Douglas

[shorty]

Not to get off topic but, is PikeP AKA Ackuric ?

[oldpro]

Not to get off topic but, is PikeP AKA Ackuric ?

Yes

[mann]

I'm thinking about building another balance valve and use the 25 mrod original valve and I may order a Breech and put another  marauder together  . Question I have is how far can I open the throat on the original mrod valve 
Tia mark

[PakProtector]

If you don't touch the seat on a 2563 valve, you can take the throat to about .234" Now if you have a 2263 valve, and you pull the sleeve, you can go significantly bigger. Now I am going to find out if the 2563 body can stand having its OE seat removed, and re-created after turning it to chips with a .281 drill. The remaining knife edge seat will need flattened, so a turned dowel chucked in the lathe and sandpaper glued to the flat end should do...
cheers,
Douglas

PS: WTB any/all 2263 valve bodies...

[mann]

I wasn't to worried about the original seat I just didn't want to get into mounting screw holes .280  was about where I want to be

[rsterne]

Well, it's been an interesting and educational couple of days.... The smaller balance chamber REALLY changed things.... I had installed the .308 cal. upper on the gun before testing, even though I know it's not a good idea to make 2 changes at once....  …. I still had the same hammer and SSG spring installed, and with 118 gr. bullets it peaked at 846 fps (188 FPE), which was quite a drop from the 219 FPE I had with the conventional valve, which had smaller ports.... I know I have a much smaller plenum on this gun at the moment, with the tiny tank installed, but that was a big drop in power.... The tuning range, however, was much wider, now up to 200 fps with the smaller balance chamber.... I suspected that perhaps I had cut too much off the valve stem, or stacked too many O-rings on the shoulder on the poppet as a safety bumper, and that the valve was no longer able to "blow open" sufficiently to give me the power I felt I should have had.... I even tried a stronger hammer spring, and all that did was increase the SSG gap required, I could not get the plateau velocity to go over 850 fps.... At small gap settings the velocity dropped, a sign the hammer was bouncing off the back of the valve.... All in all, pretty frustrating....

I pondered it for a couple of days, and then decided that before I pulled the valve out and changed things again, I should try reinstalling the heavier steel hammer, which weighs 123 g. with the cocking handle installed.... With the shortened valve stem, the hammer stroke has increased to 1.18".... I was running low on the 118 gr. bullets, so I grabbed some of the 109 gr. HP version to continue testing.... I tried a shot with the heavy hammer spring and got well into the 900s with a big gap, so I reinstalled the 0.047" wire spring and did some proper testing with the gun tethered at 3000 psi.... Here are the results....



The velocity peaked at 938 fps at 2 turns of gap on the SSG, which with the 109 gr. bullets is 213 FPE, pretty close to what I had previously, with the full size bottle in place.... The fall off with less gap is because the hammer is bouncing off the back of the valve.... The big surprise was the HUGE increase in tuning range with the small balance chamber, about 300 fps....  …. This pretty much proves that the small balance chamber, along with a generous vent, is the key to a wide tuning range.... However, it does need a heavier hammer to create the dwell needed to get maximum power.... The valve is operating like a balanced valve on opening, but a conventional valve on closing, so you need hammer momentum to fully open the valve and keep it open long enough to get maximum power.... The efficiency is pretty decent, I have no problem with those numbers.... certainly a huge improvement with the balanced valve and the SSG.... I ran some short shot strings (still with the tiny tank, remember), as follows....



You will note the nice bell-curves, and that the fil pressure drops as the velocity decreases, just as it should.... I didn't stop the last string (in red) until the pressure was down to 1300 psi, so the valve is perfectly stable, with no sign of hammer bounce.... I also tested the maximum velocity with 4 bullet weights at 2T of gap on the SSG, as follows....

79.5 gr.... 1047 fps (194 FPE)
98 gr..... 958 fps (200 FPE)
109 gr.... 938 fps (213 FPE)
118 gr.... 899 fps (212 FPE)

To put this performance in perspective, compared to the 154 gr. bullet in the .357 cal, the 118 gr. bullet is a slightly higher SD, and yet it is shooting faster in the .308 cal, 899 fps instead of 883 fps.... so I certainly don't seem to have lost any performance with the smaller balance chamber and larger vent.... I think before I try the 7 mm upper I will reinstall the .357 upper, just make sure.... All in all, I am very pleased with the way this balanced valve has turned out.... It is MUCH easier to cock than the conventional valve, I can run an 11 lb/in hammer spring instead of the 15 lb/in spring I had previously.... with a lighter hammer, less travel, and the cocking force has dropped from 23 lbs. to just 13 lbs.... Yes, I had to reinstall the steel hammer from the .224/.257 cal version instead of the MDS hammer, but the range the valve can be tuned over is now double what I started with (actually, the original version of this valve was not tuneable at all)…. I would say this valve is a screaming success.... 

Bob

[mann]

Yes it is a great success good job Guys

[rkr]

I'm wondering how it would work if you left the valve spring out? That would allow even smaller chamber in the thimble. Or perhaps use a weak spring from thin wire that would just have enough power to push the valve against the seat when the gun is empty.

[MJP]

The spring is not needed, at least I have not found any use for it. 

Marko

[rkr]

The spring is not needed, at least I have not found any use for it. 

Marko

Well, it could be useful to get the fill started with an empty gun. IIRC some guns without valve spring require a very healthy blast of air from the tank to get started

After drilling 4 thimbles off the center I started thinking that perhaps there's an easier way of doing it - extension nut + some thread bar or extension stud. Just drill out the threads for the chamber and screw in a thread bar that attaches thimble to the valve housing.

https://www.ebay.com/itm/M3-M4-L-6mm-Hexagonal-Hex-Thread-Extension-Brass-Studs-Pillars-Standoff-Spacers/132771163663?hash=item1ee9c72e0f:m:mku3oMYAmH78XxWnb_o2AKg:rk:8:pf:0

Now if I wanted to use a steel extension nut + thread bar for extra strength, could locktite or epoxy be used to form a pressure tight bond in the threads?

[TPL]

Epoxy will do the job well, just remember it's not so strong mechanical bond where that is needed. It is preferable as sealing, no guessing if it hardens and it is easier to open than locktite. Just a little warming is enough.

[rsterne]

After seeing what happened when I drastically shortened the balance chamber in this valve, I think I have a "rule of thumb" for how much travel you need to allow for in one of these valves.... This is also based on the lift measurements I have done on this and other valves.... Originally I had 0.250" of room for the poppet to lift before the small end bottomed out in the thimble, or the spring went coil bound.... I shortened that to 0.150" of physical room, then limited that to 0.140" with the O-ring bumper riding on the poppet, and then shortened the valve stem so that the hammer could only drive the stem 0.130" before it hit the back of the valve.... This provided a couple of safety margins so that the poppet could not crash into the end of the chamber in the thimble with great force and end up destroying itself.... I had determined with my lift measurements that 0.125" of available lift should be enough to give full power with the 0.375" throat diameter of my valve....

Now that I have tested the above, while I still think that having 1/3 of the throat diameter for the poppet lift is probably enough to provide full power.... I don't think I have really left enough travel inside the valve.... I think it likely that the valve is still "blowing open" to some degree, and the poppet may be travelling far enough for the O-ring bumper to be limiting the travel.... While that is its intended job, I think I have gone just a bit too far for the ultimate safety and longevity of the valve.... I think a better way to go would be to allow for a poppet travel of 1/2 the throat diameter, or 0.187".... I would then make sure that the hammer could not drive the stem physically past about 0.150", have the O-ring bumper hit at about 0.170", and still have a safety margin of 0.017" to allow for O-ring compression....

The next time I have the valve apart (which may not be for a very long time, or may be tomorrow) I will carefully examine it for any signs that the end of the poppet has bottomed out in the thimble.... Perhaps it hasn't, and this precaution is not necessary.... However, I feel that if followed, this guideline (allowing for 1/2 the throat diameter for maximum poppet travel) should avoid any damage.... when accompanied by a stem length that will prevent the hammer from driving the poppet that far....

Bob