ATI Libert/Freedom Custom valve

[FuzzyGrub]

Oh BTW, if you guys thinking about tapping the plenum for a 1/8 npt gauge. dont do it, the hole is 0.351 and the 1/8 npt thread calls for a 0.328 hole. i had to Jbweld rated for 5000psi for peace of mind. i only had maybe 0.200 worth of proper engagement area at 0.328 hole. i tested it to a 4000psi fill with regulator spiked to 3800psi from 3600psi set. it may work fine but i would feel better if it were correct in size. so i am not recommending you go that route.
 when my metric die gets here next week i can make an adapter to the plenum i would feel a lot better

Bummer!   I think 0.351 is too big for a M10 gauge, too.

[rsterne]

As I stated earlier, the "trench" in the DR-TR increases the volume between the valve seat and the pellet.... which causes a pressure loss.... I would expect a slightly lower velocity compared to a valve having equal port sizes but with minimal wasted volume.... such as the DC-10A....

Bob

[cosmic]

Thanks Bob !! Your knowledge is gratefully accepted by all here !!!

[Madd Hatter]

As I stated earlier, the "trench" in the DR-TR increases the volume between the valve seat and the pellet.... which causes a pressure loss.... I would expect a slightly lower velocity compared to a valve having equal port sizes but with minimal wasted volume.... such as the DC-10A....

Bob

Bob, wouldn't the notched valve also disrupt the air flow and slow it down due to the miss match of the trench and the TP?

[rsterne]

There may be some effect from that.... but I'm guessing the pressure drop from the wasted volume is the largest contributor....

At the beginning of the shot cycle, where the greatest acceleration of the pellet occurs.... the pellet velocity, and hence the airflow velocity, is at a minimum.... Therefore, angles and obstructions are less important, it is the pressure that is doing the work.... and wasted volume between the valve seat and the pellet drops that all-important pressure....

Later in the shot cycle, when the pellet is well down the barrel and moving quickly away from the breech, the air is moving faster as well.... and corners and/or restrictions that disrupt the flow are more important.... If the valve closes quite early, when the pellet velocity is low, they are less important again.... That is why large porting helps get more maximum power from a PCP.... but has less effect on a detuned one....

Bob

[darkcharisma]

Hi Bob,

good points on the airflow and pressure and i agree on the mismatch ports play a minor role in fps than pressure in each shot. though best airflow is always better.

i am interested in the DCTR using 50psi per shot and gets to 52fpe while the DC10A uses 100psi per shot and gets 55fpe. 3 fpe difference but DCTR would get twice the shot counts due to the 3-4 times stronger valve spring i used during the last test.

also think the DC10A can get 50psi/shot efficiency by adjusting hammer strike. both valves can be further improved with smoother edges too.

DCTR   has 1.35" stem length
DC10A has 1.24" stem length

I feel the DCTR can get close to 55fpe if the ports are larger than .245x.195, say .255x.217? more tests coming
=============

[rsterne]

Comparing the air use at different velocities in not the correct way to go.... Depending on the dwell, reducing the velocity just 3 can sometimes cut the air use in half.... Tune them to the same velocity and then look at the pressure drop per shot.... Additionally, velocities around 1000 fps and more tend to be real Air Hogs, depending on the barrel length....

Bob

[darkcharisma]

Got it, it was just a comparison between valve designs to see which is better between trench vs no trench. i forgot i used a stronger spring in the DCTR valve.

you have done more testing than i have so i need to take some pointers in how best to tune for efficiency after all the tests.

[rsterne]

Duy, if you are trying to compare two valves, IMO you should do one of the following....

1. Change NOTHING else in the gun, not pellet, pressure, transfer port, hammer, spring, preload, not anything.... OR

2. Leaving the pellet, pressure and porting the same, maximize the velocity with each valve, by changing the hammer strike until you reach the plateau, where additional hammer strike does not increase the velocity.... THEN you will know the maximum each valve can deliver....

If you make any other changes when you change valve, you cannot tell you what the valve is doing, and what your other changes are making.... with the exception of how much power the valve can deliver on the plateau.... Once you find the plateau with each valve, then detuning 3-5% from that velocity, and tuning the valves to the SAME velocity, will allow you to assess the efficiency....

Bob

[darkcharisma]

Thanks Bob,

i changed nothing in the gun. just the valves. except one used the stronger spring and one used the lighter. now i need to retest the DCTR with a lighter spring. the hammer is at max with added weight. reg pressure stayed the same.

yup, ill throw in some more mods to get more power then detune for efficiency. 100psi/shot for 55fpe is not worth it compared to 50psi/shot for 52fpe. and i dont need to run the gun at 3600psi either.

ideally i would like to run at 3000psi with the bigger plenum. and still making 50-55fpe or something like that for more shots.

[rsterne]

except one used the stronger spring and one used the lighter

That change means you can not draw any conclusions from your test, IMO....

You need to try changing the hammer spring preload to find out what the plateau velocity is.... ie where increasing the hammer strike further will not gain more velocity.... and do that for BOTH valves.... Only then will you truly know which valve can supply the most power....

After that, then you can start reducing the hammer strike until you get them both to shoot, for example, 900 fps.... THEN at that setting compare the amount of air used.... Then you will know which valve is more efficient, and what the difference is....

Bob

[darkcharisma]

thanks Bob, a while back i forgot i used a stronger spring on the DCTR test. i sure screwed it up. testing is time consuming...but there will be another.

anyhow, its not as time consuming as this item i made. an extended power wheel with a digital gauge adapter, guess how many hours? i went Slow...i mean sloooow to avoid breaking the carbide micro grooving tool. those things cost $60 a pop and i broke 1 a month ago.

heres a preview of what a 416 stainless power wheel looks like pre heat treat. i keep one made out of O1 to remind me rust is not our friend.

I cant wait for the tests this weekend, i am chasing the exact pressure inside the exhaust of each valve.

[Backyard Shootr]

That digital gauge is cool. Never seen them before. Do they need battery's to function? 

[darkcharisma]

That digital gauge is cool. Never seen them before. Do they need battery's to function?

sure they do. edgun west product. $90 shipped on their  website. this tells you alot of stuff, it calculates remaining shots based on pressure loss...etc its a neat toy.

[rsterne]

Does the gauge have a "hold" function, and a fast enough response time to record the pressure in the exhaust port?.... The pressure peak will occur for less than a millisecond....

Bob

[darkcharisma]

i just got it the other day, so ill need to dig into it and find out what it can really do. there are other digital gauges for the purpose, probably. But its a starting point. if it doesn't work, i'll have a novelty power wheel. lol

[cosmic]

Here is the manual.. It does say it will do air use per shot.. But whether it will work in this application ?
https://www.krale.shop/media/blfa_files/Handleiding_-_Digitale_Manometer_Edgun_EDMU_EN_.pdf

[rsterne]

I don't think it has a "hold" function for the peak pressure encountered, which is what you need to measure the peak pressure in the exhaust port.... JMO....

Bob

[darkcharisma]

Bob, which digital gauge has that function? or should i have to frankenstein a pressure transducer and the likes?

[rsterne]

I don't know of any, particularly with the response time you would need.... I guess a pressure transducer would do the job, but I don't know anything about them.... Don't forget, any volume you add inside the adapter and gauge will alter the pressure reading....

Bob