ATI Libert/Freedom Custom valve

[huklbery]

Next I need to make a plenum butt plug with a gage.  This exercise leaves me wondering where on the pressure scale my two samples are now.   

Yes, it comes off the reg so gradual, it is hard to tell exactly where the set-point is. 

What porting are you running?

This one's running a .187 barrel and a taper reamed adjuster (up a bit dimensionaly not certain how far but less than 3/16")

My friend is running his stock and mainly shoots budget CHP's.  As he is a hand pumper (degassing is serious work) and frugal (Cheap 14.3g shoot sweet) he is perfectly happy with it as delivered.  He is certain his sample by seat of the pants testing he gets best point of impact repeat ability from 3500 - 2500 psi on the tiny gauge.  His drops POI when he fills off the bottle to above 3500psi towards 300 BAR.   

My goal is get one shooting 18.1 JSB's right at 900fps (The JSB's in 500 tins are much better cost ratio than the H&N 21g baracuda's in 200 count tins)

The second I want to push up to 40ftlbs for slugs again at 900fps, smallest practical slugs seem to be 22g if I'm doing the math correctly. 

I'm not sure how it all balances out as far as efficiency, bounce loss and all the usual variables.  I'm guessing that the least strike force with optimum regulator pressure will be trail and error.   

[FuzzyGrub]

Looks like you have a few slots left for some more Libertys. 

It is easy to get 30FPE, which is what I consider a good 22 hunter.   Using Stephen's slugs will be trying to get them over 900fps, for hopefully a good 100yd shooter.   

[Madd Hatter]

Next I need to make a plenum butt plug with a gage.  This exercise leaves me wondering where on the pressure scale my two samples are now.   

Yes, it comes off the reg so gradual, it is hard to tell exactly where the set-point is. 

What porting are you running?

This one's running a .187 barrel and a taper reamed adjuster (up a bit dimensionaly not certain how far but less than 3/16")

My friend is running his stock and mainly shoots budget CHP's.  As he is a hand pumper (degassing is serious work) and frugal (Cheap 14.3g shoot sweet) he is perfectly happy with it as delivered.  He is certain his sample by seat of the pants testing he gets best point of impact repeat ability from 3500 - 2500 psi on the tiny gauge.  His drops POI when he fills off the bottle to above 3500psi towards 300 BAR.   

My goal is get one shooting 18.1 JSB's right at 900fps (The JSB's in 500 tins are much better cost ratio than the H&N 21g baracuda's in 200 count tins)

The second I want to push up to 40ftlbs for slugs again at 900fps, smallest practical slugs seem to be 22g if I'm doing the math correctly. 

I'm not sure how it all balances out as far as efficiency, bounce loss and all the usual variables.  I'm guessing that the least strike force with optimum regulator pressure will be trail and error.   

Mine's doing 924 avg with just the .100 shim HS and 1/4 turn CCW on the reg. with the JSB 18.13. 22 shots and only used 800 psi to do it.

[wll2506]

the liberty's hammer is made of feathers. even with the extra hammer weight i put in Rays gun it is now unable to knock open the valve. making the rifle very efficient right now. when at first i tested it, i was getting 15.5 grains nsa slugs to go 980fps. now? with a 4k fill it will do 550fps and 880fps with 18grs at 2800psi. this is all from increasing the reg with no gauge.

3000psi would need some heavy hammers. it may already be at 3k on Rays gun. sorry Ray you gotta turn it down

I'm going to add a weight inside my hammer spring in my Liberty, is 5/8 long OK or can I get away with 3/4 of an inch ? Trying to get another 50 fps without adding more PSI to the regulator, or another shim (with this added weight) I will remove one shim I think as I may not be able to cock the gun with any extra length ?

wll

[darkcharisma]

it just don on me that i dont have a valve of my own. i need to machine a pair and start testing, sorry if i hyped you up for the plenum test the other day.

Robert, thats actually a very good shot count and consistency. take a shim off and see if it gets better.

Mark, it sounds like you are chasing power but also shot count...why dont cha make a fix powerwheel and port it to 3/16 through? i bet you the plenum will do some good, given your valve is modded too.

Will, 1/4 on top of spring. 1/2 inside spring. so 3/4 total length give or take.

so Ray gave me a teaser today and yesterday. yesterday he gave me a report of the .177 15.5gr nsa slugs going 1060fps at 3300psi, but at 3600psi or 4000psi it was only going 500fps. something tells me the regs gone hay wire above 3300psi and the hammer just cant bounce it.

today he gave me a shot string of the H&N Excite Hammers 7.87 double fed to 15.76grs. see attachment below. and he said he would do actual numbers shooting Nsa 15.5gr and 18grs morrow. Brother Ray, i got patience...LOL

from this data, in exchange for power the cost is horrible efficiency! pellets going 1145fps will usually result slower with slugs, say 39-40fpe. thats not bad for a .177. shot #6 is probably single load. shot 5-12 gives tight es. we can tune it down for efficiency later. still not sure what the reg is set at. will gauge it later. it seems to work around 3300psi if set high.

[Madd Hatter]

Duy, all I've done in the way of shimming the HS is I added 1 .05 washer for a total of .100.  mine actually seemed to reg at 3800 psi since I opened up the reg vent hole a couple of thou. It may have just been plugged with the silicone oil I used on the belvenue washers so opening it up may have done nothing but cleaned out the vent. My vel did go up once I reached about 3300 psi about 20 to 40 fps.

[rsterne]

I have been asked for my input, but I really don't know anything about this gun.... I must admit this thread seems to be going in several directions at once, and is hard to follow.... However, here are a few things I noticed....

You tried a longer stem and lost power.... That is because you have reduced the hammer travel, energy and momentum.... Unless the valve is not opening far enough, you do NOT need to lengthen the stem.... PCP valves only open about 1/4-1/2 the throat diameter, and when operating efficiently, closer to 1/4 or even less.... If you allow 1/2 the throat diameter for stem travel, that is plenty.... Therefore, assuming the hammer can reach the back of the valve when firing, if the throat is 1/4", if the stem sticks out 3/16" you will never need more, because when operating the valve will only open 1/16"-1/8"....

It looks to me like you are adding a plenum where the gauge port is?.... That will work fine if the passage between the plenum and the valve is larger than the valve exhaust port.... If it is significantly smaller, the flow out of the plenum into the valve won't keep up with the flow out of the valve, so you will still get some pressure drop at the poppet, and hence at the pellet.... The whole purpose of a plenum is to maintain the air pressure at the pellet as high as possible, compared to what you started with....

While I try and design plenums for 1 cc per FPE, when you are installing a regulator inside a tubular reservoir, that means you have to give up too much of the HP air volume.... so 1/2 cc per FPE is often better.... However, you will have to increase the setpoint pressure about 10% to make up for the smaller plenum....

Bob

[Madd Hatter]

We're actually trying to increase the capacity of the plenum from around 10CC up to.... Don't remember what Billy made his to for testing but I think it was 30 or 40cc. The plenum is installed into the bottom of the receive and the gauge is at the end of the pressure tube near the muzzle. What some of us want is a gage installed at the bottom of the plenum so we can see where in the heck the reg is set at. Try shooting the rifle down from pressure isn't very consistent as it has a lot of creap.

[huklbery]

The storage tube connects to the external regulator block (its the block with the long degassing screw and burst disc. 

The plenum is installed in an external drop reservoir on the receiver (10mm x 1.25 not sure what the diameter of the inside hole is off hand, the back plug hole is 16mm x 1.25 with a 9mm inside through hole).

It's rather small at 10cc or so.  By doubling it with an extension it increased fps from 931 to 959 with 18.1g in this current state of tune. 

[darkcharisma]

your input and other's inputs are always encouraged. this thread really is about the pursuit of power, so anything plenum, valves and in between is good for me. i am learning as i go. and thank you for providing some infor into The technicals.

this gun has a 200cc tube that can get to 300bar fill. it has a in breech regulator and a 5.2 cc screw on plenum and 3cc plenum in front of the valve From .547 diameter by 3/4 of an inch. The OEM valve has a trench cut and can do 45-50fpe with ports, hammer spring shims and turn the reg up via an adjustable brass wheel. I am just trying to copy and enlarge

I would agree that we somewhat loose power due to cutting short momentum and hammer travel. Because it is indeed looooong. However, with Rays testing results, I think the stem prooved to be working ok with the current hammer strike, but it's true we don't need that long of a stem since efficiency is hurting. Thanks again for the technical recommendations.

The low velocity you see when the gun is filled to 4000psi is probably due to reg creep. I.e if we set the reg at 2.6ksi it may be 3ksi if we fill it to 4ksi. This is a common problem with the ATI liberty. And I suspected the low fps is due to not having enough hammer strike on the high reg creep. I could be wrong.

I'll apply some of the measurements given here on the next valves. I am glad it is constantly being improved... . we will see how it performs with some tests.

[rsterne]

It looks to me like the hole in the original plenum extension is about 5 mm.... Having larger holes between that and additional extensions is good, but will not increase the performance, other than through the gain in volume (whereas a smaller hole would limit gains).... Assuming that 5 mm hole is the smallest restriction between the plenum extension and the valve poppet, it should be large enough (barely) to not drop additional pressure due to a flow restriction.... although I prefer any holes on the inlet side of the valve to be larger than the valve throat, to guarantee there is no addition pressure drop.... Judging by the amount of metal between the hole and the bottom of the threads, I would not drill it out larger for safety reasons.... unless you know the materials, exact dimensions, and do the calculations for a 4:1 safety margin....

If the regulator output is varying 400 psi between a 3K fill and a 4K fill, they need to design a better regulator.... That is unacceptable pressure variation, and it is NOT creep.... Creep is when the regulator pressure changes over time (eg. continuous shooting or leaving the gun sit for a week under pressure)…. Even so, if the gun is properly tuned, a 400 psi pressure change would not drive the gun into valve lock.... It sounds to me like you have insufficient hammer strike, and that could easily be due to the longer valve stem reducing the hammer stroke.... JMO, having never played with one....

Bob

[huklbery]

It looks to me like the hole in the original plenum extension is about 5 mm.... Having larger holes between that and additional extensions is good, but will not increase the performance, other than through the gain in volume (whereas a smaller hole would limit gains).... Assuming that 5 mm hole is the smallest restriction between the plenum extension and the valve poppet, it should be large enough (barely) to not drop additional pressure due to a flow restriction.... although I prefer any holes on the inlet side of the valve to be larger than the valve throat, to guarantee there is no addition pressure drop.... Judging by the amount of metal between the hole and the bottom of the threads, I would not drill it out larger for safety reasons.... unless you know the materials, exact dimensions, and do the calculations for a 4:1 safety margin....

If the regulator output is varying 400 psi between a 3K fill and a 4K fill, they need to design a better regulator.... That is unacceptable pressure variation, and it is NOT creep.... Creep is when the regulator pressure changes over time (eg. continuous shooting or leaving the gun sit for a week under pressure)…. Even so, if the gun is properly tuned, a 400 psi pressure change would not drive the gun into valve lock.... It sounds to me like you have insufficient hammer strike, and that could easily be due to the longer valve stem reducing the hammer stroke.... JMO, having never played with one....

Bob

Your eye calibration is correct, 5mm and 9mm respectively.  Back chamber is threaded for 16mm 

[darkcharisma]

i was just throwing out an example since i don't have a gauge on there to read the current reg. i will shorten and verify. but i found this post by Billy, since he got a gauge on his Liberty. i'd take his words for it.

i am thinking of scrapping the reg and build a block for bottle regs...okay okay, i need to stop throwing wild ideas out here

[wll2506]

the liberty's hammer is made of feathers. even with the extra hammer weight i put in Rays gun it is now unable to knock open the valve. making the rifle very efficient right now. when at first i tested it, i was getting 15.5 grains nsa slugs to go 980fps. now? with a 4k fill it will do 550fps and 880fps with 18grs at 2800psi. this is all from increasing the reg with no gauge.

3000psi would need some heavy hammers. it may already be at 3k on Rays gun. sorry Ray you gotta turn it down

I'm going to add a weight inside my hammer spring in my Liberty, is 5/8 long OK or can I get away with 3/4 of an inch ? Trying to get another 50 fps without adding more PSI to the regulator, or another shim (with this added weight) I will remove one shim I think as I may not be able to cock the gun with any extra length ?

wll

I need to shorten up about another 1/8 inch I think, could not cock the gun !

wll

[darkcharisma]

making a valve for Gary and refining as i go. looks like the shape should allow for better flow. following Billy Rohm's advice. hope it will seal or it will be back to the simple poppet.

[cosmic]

SWEET !!

[darkcharisma]

I went ballistics on the angles and smoothing out for better flow. looks like i can test this new puppy as soon as my replacement oilless compressor comes in a few days for the shoebox.

note. it looks like a funnel even the valve face has an angle.

[darkcharisma]

Took a day off but working to the AM now. got a nice radius with .257 throat and a .195 exhaust at an angle. testing coming soon

[Madd Hatter]

Do like the HP crowd does and do a 5 angle where the valve contacts.

[darkcharisma]

a little more precise Robert? what contacts what? give pictograms 

i am not too familiar with what the HP crowd does