2400kt, Bottled, Regulated

[aPpYe]

Actually, now that I think about it, when initially pumping up a tank, you are taking a large volume of air that contains an amount of heat and compressing that air, along with at least some portion of its retained heat.  When room temperature air is continually compressed into the tank the temperature will continue to rise because you are taking a large volume of warmer air and putting it into a smaller space.  I would imagine this increase in heat rises by some mathematical number in relation to the speed at which it is compressed.  This compression is what causes the heat to rise in a diesel engine cylinder, allowing the fuel to combust, which is similar to what happens when a springer "diesels"...

I am pretty sure I have read somewhere that there are those who have attempted to take advantage of this to increase velocity... I gotta read on whatever results people have had... I wonder if it can be reproduced with a level of consistency that would allow for consistent fps.  I am sure someone has tried...  On to google!

[aPpYe]

Okay, so in playing around with pressures, and being really happy with the fact that I did not have any leaks, I figured I would go with a full bottle.  I started by going up to about 3100psi in my living room which was 69 degrees, according to the thermostat.  Putting it in the cold guest room brought it back down just below 3000 psi and bringing it back in the living room got it back to 3100.  I even put it in the freezer and saw the pressure drop down to about 2600psi.  After sitting in the living room again for about an hour it was back to 3100, so I thought I would see how high the pressure would go on a hot day.  I started by holding the bottle under my arm pit for a while and was able to get the pressure to rise to about 3400psi or so.

... Then I was holding it in my hand and watching TV and the 1.8k disk blew!  I am thinking that while the bottle was in the freezer, regulator pressure also dropped and allowed more air into the outlet side.  When the temperature rose back up, this additional air brought the outlet side to whatever increased pressure finally blew the disk.  Maybe it has something to do with the fact that I calibrated the regulator to 1450psi with 3000psi in the bottle while I was in my garage that was probably about 50 degrees.  Not sure about that one...   

I ordered a two pack of 1.8k disks off of ebay for 3.95 with free shipping.  Not bad!

Anyway, I am going to put the 5k back in there and see what these temperature variations do to output pressure. 

Speaking of that, I may have to rethink my whole 45 degree fitting idea.  I did not realize how little thread is actually engaged when using NPT...  The female end of that fitting is going to be sitting much higher than I originally thought!  I kind of wish we could use straight thread everywhere instead ... it seems superior to me, especially since it does not rely on deforming the threads to make a seal.  I would think npt threads would be much less reusable.  Oh well, maybe that could be a project for another day.  Or I could just buy new fittings every once in a while...

...aaaand I am done rambling.

[aPpYe]

Yep, confirmed.  I filled to 3100psi in my living room and saw somewhere between 1425psi and 1450psi on the reg tester.  I put it in the freezer for an hour or so and saw bottle pressure was down to about 2600psi, while the output pressure remained unchanged.  Now that the assembly has been removed from the freezer for about 30 minutes, I am seeing 1650psi on the output side and it is still cold in my hand.  Bottle pressure still shows about 2900psi so I would think we will still see some pressure increase.

I guess this means that it would be a good idea to let some pressure out of the gun after bringing it into the house, if I am going to continue to have the regulator set this close to the 1.8k burst pressure I plan on having on the gun.

... Since the gun will likely arrive before the new burst disks, I will be keeping things under 2000psi while doing my initial tuning and whatnot, as I like my arms and legs intact.  I figure I can at least get a lower resolution idea of where the gun is tuned based on RVA turns...  I figure I will be looking at a single 500psi increment (2000psi down to 1500psi) on the ninja gauge, rather than seeing performance over the broader spectrum of a full bottle fill.

[rsterne]

As the tank cooled, it let a bit more air into the bonnet to maintain 1450 psi.... then when it warmed up, that air expanded and increased to 1650.... This can cause a marginal burst disc to fail, but is not an indication of a regulator problem, and is to be expected....

When tuning the RVA, you should find that above a certain preload you get no further increase in velocity.... Tune for the point where the velocity just starts to drop for the most power with efficiency.... If you want less power, then decrease from there.... but be advised that if you drop down very much, the velocity will INCREASE when the pressure drops below the setpoint of the regulator.... just like in an unregulated gun (velocity increases initially as pressure drops)....

Bob

[aPpYe]

I am thinking this will not be much of a problem here, as it rarely gets below freezing here before 3am, and even the colder daylight hours generally rise pretty quickly above 50(F) here in the winter ...

I figure I will still occasionally dry fire the gun if I haven't fired it after some time, that is if I ever recover from this airgun frenzy I am hopelessly addicted to at the moment! 

[aPpYe]

Heh heh ... yeah, I am seeing about 1725psi on that thing now that it has been out of the freezer for some hours...  No wonder the disk burst.

[aPpYe]

Not sure how I feel about this ball valve design.  A coil spring holds the ball up when there is no pressure in the bottle.  This has happened to me a few times now when I evacuate...  Twice I have had this issue, and one time, the oring wasn't even off center like this, the ball pushed into the oring hard enough to stretch it to the side... I have to remove the bonnet, pull the stack and reseat the ball, spring and gasket to fix things... 



...I am thinking of using this silicone goop to keep the oring in place, maybe even using it instead of the oring.  I dunno ...


sigh.

[rsterne]

Post those photos in the Ninja gate and have Ray comment....

Bob

[BigTinBoat]

Not sure how I feel about this ball valve design.  A coil spring holds the ball up when there is no pressure in the bottle.  This has happened to me a few times now when I evacuate... 

I think you may be "Evacuating" too quickly. This cools the seals to a point that they are distorting.

Also with your pressure going up to over 1700 it sounds to me like you are getting regulator creep. I've had 2 of my bottle at 1500 for a few months now and the reverse bottle gun has a gauge between the gun and tank. Never has it gone up over 50psi between temperature changes.

[WECSOG]

sigh.  I need to stop using my phone on this forum.  I was referring to the little green oring that is in between the ball and the housing.

Autocorrect passes me of.

Steve

 
Passes me of two.

[aPpYe]

Post those photos in the Ninja gate and have Ray comment....

Okay, will do... This keeps happening!  I am not sure if the oring is too soft or what ...

I think you may be "Evacuating" too quickly. This cools the seals to a point that they are distorting.

Also with your pressure going up to over 1700 it sounds to me like you are getting regulator creep. I've had 2 of my bottle at 1500 for a few months now and the reverse bottle gun has a gauge between the gun and tank. Never has it gone up over 50psi between temperature changes.

Initially, I did evacuate (is there a proper term for this?) rather quickly, and I ran into the distorted oring, so the problem may well be due to the oring having become distorted in the first place.  What I have been running into probably about 5 times now is definitely not because of evacuating too quickly.  I have an ASA attached that has a built in degasser, so I SHOULD be able to back out the pin and it evacuates the gun but not the bottle.  This usually works about three or four times before the oring is once again out of place.  Then I once again have to pull the bonnet apart and reseat the oring.  Very frustrating.  I am at this point wondering if it is possible to just get the standard pin and replace the ball design with that. 

As for the regulator creep, I am thinking that this is not what happened.  I am able to reproduce the effect reliably by dropping the temperature and bringing it back up again.  I actually saw the pressure rise well above 1700 when I left the bottle in the freezer for several hours, then looked at it the next day after it warmed up again.  If the regulator was "creeping" I would see the pressure rising regardless of temperature, correct?  I am not seeing that happen, as I have seen it hold pressure for several days so far...



Anyway, I got my gun last night and tore into it right away!  I pretty much got it all together now, except I am gonna have to run into town tomorrow to get a 90 degree fitting and maybe shorten my hose or buy a shorter hose...  The 45 certainly doesn't work as I had originally thought it would. The gun sure sounds impressive when I dry fire it though!  With the 24 inch barrel, it sounds much bassier than my silver streak, which has a higher pitched crack.  It is actually quite a bit quieter.  I have yet to send a pellet through it...

I also screwed up with my valve pin locations. One of them was ridiculously off center!  If I do this again, next time I will start with MUCH smaller holes so I can see where I am as I get the dremel and start enlarging them.  After a few expletives and some careful grinding, this is the hack job I have now.  Feel free to chuckle:



I actually had to make the factory valve pin hole a little oblong in order to make them all match up as well as I could.  I figure oblong doesn't really matter since we are only dealing with pressure in one direction...  I made them all match up at the rear of the gun as best I could.

Of course, now my transfer port is slightly off center.  I am not sure if I am gonna be able to do anything about that...

[rsterne]

Hard to tell from the orientation of the photos, but if all three screws are resting against the rear of the holes it should be safe enough.... but a closer fit would be better, of course....

If you enlarge the exhaust and transfer ports, just work on the front of the exhaust port with a Dremel to re-center it in the hole....

Bob

[aPpYe]

Okay, so the exhaust port is the hole in the valve and the transfer port is the hole in the tube, correct?  This leaves the sleeve and the face seal (according to Crosman's EVP for the Disco)...

I would actually like to push things rearward a tiny bit more, because the screw that is going through the word, "warning" is not quite sitting against the tube.  I got a little overzealous with the dremel.

If I enlarge the exhaust and transfer ports, wouldn't I also need a larger sleeve and face seal?

What kind of performance deficit am I looking at if I leave it off center?  I had thought about enlarging the holes yesterday but I remembered you told me earlier that going with larger porting might actually cause me to lose performance in .177 ...

[rsterne]

The transfer port is the metal sleeve and it's associated rubber seal.... It is the piece that transfers the air from the valve to the barrel.... The exhaust port is the hole in the valve facing upwards.... Below that, facing forwards, is the throat.... The hole in the barrel is the barrel port....

I forgot you were doing .177.... probably no need to make anything larger, a slight amount of misalignment probably won't make any difference.... I've seen ports out that far in a new gun....

Bob

[Sfttailrdr46]

Actually, now that I think about it, when initially pumping up a tank, you are taking a large volume of air that contains an amount of heat and compressing that air, along with at least some portion of its retained heat.  When room temperature air is continually compressed into the tank the temperature will continue to rise because you are taking a large volume of warmer air and putting it into a smaller space.  I would imagine this increase in heat rises by some mathematical number in relation to the speed at which it is compressed.  This compression is what causes the heat to rise in a diesel engine cylinder, allowing the fuel to combust, which is similar to what happens when a springer "diesels"...

I am pretty sure I have read somewhere that there are those who have attempted to take advantage of this to increase velocity... I gotta read on whatever results people have had... I wonder if it can be reproduced with a level of consistency that would allow for consistent fps.  I am sure someone has tried...  On to google!

Yes the same principal applies to air conditioning and refrigeration and the heat is moved to somewhere you don't care about. With the air bottles that is not an option unless you put it in an ice chest and cool it down as you fill but then you could easily over fill the tank

[aPpYe]

So my 45degree fitting idea was a bust!  I did not know that npt fittings typically leave a lot of thread showing.  The resulting fit had the hose rammed up against the barrel, or the bottle hanging way off of the tube.  Really ugly!   Oh well, I am sure I will find a use for the fitting down the road...  I put a 90 degree street elbow on there and the bottle now goes flush with the tube nicely.  Of course I think I am gonna have to head back to the Parker store and get a pipe nipple and regular 90degree female-female elbow, as the fill nipple on the bottle doesn't quite clear the threaded hose...  Maybe just a small female to male nipple, if such a thing is readily available...

Anyway, I am trying to figure out if I want the bottle right up against the tube or against the barrel band.  Any thoughts on floating the barrel  (removing the barrel band) with this gun?  I figure I would want to put in another couple of set screws (at 120 degrees) if I were to do so... I suppose I could even set it with four screws...

Also, I am a big boy now!  I couldn't get any of my tablet or smartphone chronograph apps to agree on a reading so I picked up a real chronograph.  I went with the Caldwell because it was cheaper at my local sportsmans warehouse...  The concept of these auditory chronographs seems to make sense, but likely I would need to be in a large field or on a mountaintop somewhere with no echo...  Oh well.

[aPpYe]

Beuller?

[WECSOG]

Congrats on moving up to real tinkerer/tuner status with your new chrono!
I don't think free floating the barrel will cause any problems.

[aPpYe]

Hmmm.   So I am thinking my I might have to clip the hammer spring or something.  With 1450psi reg pressure and a few turns in on the RVA, the gun averages maybe 925fps (I need to verify this) with the 10.34gr JSB heavies...  However, with any of the lighter pellets, they all start at over 900fps with the RVA turned all the way out, and accuracy is suffering.

... I am trying to decide if lowering the pressure or clipping the spring would be the right way to go.  I wouldn't mind lowering the max FPS with the JSB heavies to maybe 875 or so, but I want that velocity to be as efficient as possible, in the "knee" of the curve as Bob so famously preaches...

Suggestions?

[rsterne]

You need to try a variety of hammer spring preload settings and graph the velocity vs. preload, like this.... The knee on this curve is 4-5 turns out....



Once you know what the curve looks like, you will know if you can reach the knee, or it you need to clip the spring.... it will also tell you if you need to change the pressure.... Do that and post the results....

Bob