Prod + HUMA regulator potential-Update

[lloyd-ss]

After reading a bunch, and some PMs, and emails, and some pondering, I decided to start all over on tuning this P-Rod with a Huma regulator.  Miguel and I talked too, because I didn't want to hijack his thread.  The P-Rod is such a fun gun, and the Huma is such a great addition to it, I didn't want to do a half-way job on setting this thing up.  As  rsterne, Mr Methodical  said, don't be lazy, do the preliminary testing and graph the results and see what pops out at you. So that is what I did.
Most of the methodology that I am presenting is old news to many folks, but I am learning a lot doing this.  Also, I am presenting the data in a slightly different format, that helped me see some of the trends.
First, here is a picture of the Huma P-Rod reg.

HUMA P_ROD REGULATOR


It is a cute little thing, and appears to be very well made. It uses about 7ccs of space in the main air tube. The brass adjustment screw is the high pressure end.  The tape with the pressure settings seems to be well calibrated. The tube at the top is a plenum sleeve with 2 face seals that can be used to replace the pressure gauge adapter and the associated dead space. You can see the little atmospheric bleed hole on the side of the reg and that is cleverly vented out thru the gage hole in the P-Rods main tube. Checking with an accurate gage, the regulated pressure is very consistent with no apparent hysteresis, and almost no creep when the gun sits idle for long periods of time. 
This is a floating base regulator, and they inherently output slightly higher pressure as the input pressure increases.  That is the nature of the beast, and only  a few complex high-end industrial regs output a consistent pressure regardless of the input pressure. Just as an aside, if you want to learn about regulators, the following site is fantastic, with lots of incredible animations and excellent tech info:

http://www.zdspb.com/tech/misc/maxflo.html

But back to the P-Rod.
I wanted this P-Rod to have good power, a flat shot string, and lots of shots with excellent air efficiency. So here are the mods (right or wrong, LOL)  to the P-Rod I am testing that I hope will aid in reaching those goals:
.22 cal P-Rod with stock 12" barrel and .125 dia barrel port.
T-port and valve ex port opened up to .140 dia.
Hammer weight reduced from 58grams down to 43 grams.
Stock .035 wire spring replaced with a .041 wire spring.
Hammer stroke shortened about one turn from max.
Plenum volume (the regulated air volume available for the shot) is 10ccs. That leaves approximately 48 ccs of HPA in this particular setup.

The following graph is only the preliminary testing that will be used to find an optimum setting for the Huma in this gun.  I used 14.5, 18.1, and 21.3 gn pellets for these tests, and pressure settings of 1700, 1800, and 1900 psi.  Some pre-preliminary testing had suggested that this was the ballpark that the would like operating in.

The results shown are for 6 different combinations of pressure and pellet weight.  For the hammer spring adjustment, I backed the adjuster all the way out CCW and then turned it in CW by the specified number of turns.  The idea is to find the point where the velocity and power start to drop off.  It only took a few shots with each combo to figure that out.

Looking at the graph, the following characteristics become obvious (thank you Bob    ).  With the same settings and pressure, the heavier pellets will always give more power (FPE). It also shows fairly pronounced "knee" points where the power starts to drop off, which suggest what settings should be used for a desired power level.  For example, if you want to shoot the 18.1 gn pellets at about 20fpe, a good starting point might be Set 3, the black line, 1700 psi, with the spring turned in about 3/4 of a turn.

So now that I have all the prelim baseline data, I will set the regulator and try some stings and see if the predictions hold out.

PRELIMINARY TUNING DATA


More to come.
Lloyd

[cilami]

Looking great Lloyd! Thanks for the effort and good information provided. Now, let's see the shot counts and ES ...

[lloyd-ss]

Based on the data in reply # 20, above, I reinstalled the regulator and shot a few strings (actually, several, but these were the final ones.)  in an attempt to get decent power with a good number of shots.  For both strings, the fill was a tad over 3000, and the ending pressure was about 1600.  The actual set pressure for both strings was about 1740psi. The velocity dropped like a rock after the last good shot in each string. This is with the standard P-Rod main air tube and no extensions or extra air capacity.   Here is what I ended up with:

24 shots 18.1gn, avg vel 682fps, avg 18.7fpe, ES 10fps (1.5%), avg air efficiency approx 1.23fpe/cuin

25 shots 14.5 gn, avg vel 747fps, avg 18.0fpe, ES 10fps (1.3%), avg air efficiency approx 1.27fpe/cuin

I think there is more work that can be done regarding balancing the plenum volume vs the HPA volume, plus other adjustments, too. Thoughts?  Any suggestions would be appreciated.
Thanks,
Lloyd

[cilami]

Yesterday I spent a good part of my day working with my Mini-Prod with the intention of duplicating Lloyd's nice shotstrings. I think I accomplished my goal. The hard part was to make a "handmade" aluminum hammer of 42 grams. Nothing to be proud of, but good enough to do a few tests (pic attached). I ran out of 18.1, so I used 14.3. In summary, this is what I ended up:

24 shots at and avg. 720 fps (16.5 fpe, ES=9 fps). A total of 396 fpe, not bad. Considering that my J. Gaska barrel is about 30 fps slower than stock, I can say my string is very similar to Lloyd's.

I am happy with this, and as LLoyd says, there is room for improvement. On the other hand, the original claim of 31 shots at 18.8 fpe seems unlikely to become a reality. As a suggestion, it would be really nice to experiment with larger plenum volume and see, for example, the max. fpe obtainable for a shot count of 16.   

Thanks vey much Lloyd for the effort and keep doing the good work.

 

[nervoustrigger]

Yeah, that seems to be the trick with regulation in a smallish tube...finding the right balance between plenum and reservoir.  That's why I was saying I commend you guys who pull off a successful tune. 

To lend some perspective, the only tune I've done to a small tube PCP was to a buddy's 1720T (same tube as the P-rod).  He wanted it set up at 12fpe so I decided to try a bstaley O-ring buffer and managed to get 34 shots inside of 4%.  The total energy for the string was 387fpe, practically identical to your result.  Granted the ES isn't as tight as with a regulator but it's perfect for duties out to at least 50 yards.  And the price was right; a few dollars on O-rings and a tin of pellets.



The tune is documented here if anyone is interested:  http://www.gatewaytoairguns.org/GTA/index.php?topic=86564.0

[Geoff]

I realize this thread is 120 days old, however it has good information in it and there are not many prod/huma threads I came across.

I installed a HUMA and while the ES is fantastic, the loss of shot count is HUGE.  I left everything as it was when I installed the HUMA and went from the shot count below to about 12 shots before it fell off reg.

I decided to back out the preload and stroke to zero turns on both just to see what happened.

first the string before the huma.  this is straight out of the box for mine



I planned on just filling to 2500 and shooting down to about 1500 and calling it a day.  Then I had a chance to pick up a HUMA, so figured why not check it out.

After the terribly short string with the prod after the HUMA install I backed everything out to zero turns and started shooting.  The RED numbers are where it was off regulation.



I would like to get as close to 30 shots as close to 15 FPE as I can get.   I will play with preload and stroke to see what I can get.   If someone who works with regulators see's something in the above string that will help be accomplish this, I would appreciate the nudge in the right direction.  Until then, I toy with the settings using blind luck to guide me.  LOL



filled to 3k PSI and reg set to 1800psi - gauge is currently installed (though I plan to remove it)

[nervoustrigger]

Geoff, how did you carve up the air tube?  Meaning, how much volume did you devote to the plenum (regulated air volume).  That will give some insight as to what is possible. 

[Geoff]

I used the stock piece they included with the huma.   sorry I have no idea what the volume is.  it looks to be the same as the one in the photo above.

I figure I will get the settings eventually, I just wanted to share what is happening with mine and maybe it will help the next person in some way.   

[robertr]

 You might already have this information but this is the procedure I used to tune my regulator after installation. I got this from XTXAIR website.

Remember the regulator will determine the maximum pelletspeed.
 Fill the rifle with air, for testing, max. 180 bar.
 Turn in hammerspring to the maximum tension.
 Do some shots and measure the pelletspeed.
 If the speed is near to what you want then continue. If not, see below.
If you get way to much speed, then lower the reg pressure a bit If you do not get enough pelletspeed then increase the reg pressure a bit. You can in- or decrease it by setting the bronze screw inside the reg. A 15 minutes turn anti-clockwise will give 25 bar increase of pressure. Please handle with care, use very small steps, it's sensitive.
 Turn back the hammerspring tension and shoot and measure the speed. Keep doing this until you see the pelletspeed decreasing.
 Now you should have a pretty well balance.

[Geoff]

thank you Robert, I will give it a try.  heck, I was going to start and zero and work my way through preload until I hit the speed I am happy with, then maybe check stroke.

as it sits now, I was better off without the reg, though I imagine with time I will change my mind.  NOT that I am unhappy with the purchase, I am just not thrilled with the shot string I currently have.   

[robertr]

thank you Robert, I will give it a try.  heck, I was going to start and zero and work my way through preload until I hit the speed I am happy with, then maybe check stroke.

as it sits now, I was better off without the reg, though I imagine with time I will change my mind.  NOT that I am unhappy with the purchase, I am just not thrilled with the shot string I currently have.   

Your welcome Geoffrey, I think there is a break in period for the regulator too, I think I read on Huma's site.

[robertr]

 Geoffrey do you have a SSG ? If not you could install one to get your lost shots back maybe.

[Geoff]

I don't have one for the prod yet, I have one in my mrod and disco and like what they do.   

[nervoustrigger]

Geoff, since the HUMA regulator replaces the gauge block, that sets its location in the air tube so I will assume you have a 10.3cc plenum as in Lloyd's documentation.  Looking at a picture of the regulator, I estimate the regulator itself occupies about 9cc but since it takes the place of the gauge block, the net loss is maybe 5cc.  The volume of the P-rod is 65cc to begin with so that means it's left with about 50cc.

Your baseline gave 72 shots at about 518fps (10.8fpe with JSB 18.1gr) before falling below the regulator setpoint of 1800psi.  That represents an efficiency of....3.08fpe/ci!  So you have the most efficient PCP pistol on the planet!

Something's amiss here but I can't tell what it is.  Are you sure about your numbers, or do you see something in my numbers above that I misread?

[Geoff]

I may not have been clear, or I am not following your question.

The long string was just out of the box as a reference point that I do with all my PCP's.   There was no HUMA in the 70+ shot string.  I was comparing what I had before to what I got after installing the HUMA (with a change to the preload).   with no change to the preload I got around 12 shots before it fell off the reg and I stopped there and changed settings to zero zero to get the 10 fpe string

[nervoustrigger]

Okay, Geoff and I cleared things up in chat.   A baseline with the HUMA installed was somewhere around 32 shots at 10fpe.  That comes out to an efficiency of about 1.27fpe/ci, quite good for a short barrel.

Still confused

The shot count was actually more like 29 shots at 10fpe, and the gauge block was still installed in addition to the HUMA.  So I get a reservoir volume of more like 40cc, representing an efficiency of 1.41fpe/ci.  Darn good for a short barrel without a SSG.

[lloyd-ss]

Geoff,
Tuning with a reg can definitely be frustrating till you get the hang of it.  I had a steep learning curve, but in the end I was pretty happy.  I looked back at my notes and various shot strings and have a few suggestions on what to try.  But if you get too frustrated, I will be happy to take the Huma off your hands, he, he. 

Like robertr said, the regulator pressure is what determines the velocity. My guess is that you have the regulator pressure set too high for the velocity that you are trying to achieve.  And you have removed the gage block, so the actual pressures are a bit of a mystery, correct?  The final strings that I shot with the Huma in the P-Rod (after I was happy with the tune)  were 25 shots, ES 1.3%, vel 753-743 fps, 14.5 gn, avg FPE 18.0, total FPE 450.  Starting pressure approx 3050 psi, final pressure approx 1600, reg set point 1740 psi.   That is just one example of a tune, and it was what I wanted.

Like I said, you probably have the reg set point too high and have detuned the gun to work at the higher pressure, and then you are falling off the reg after only a few shots while you still have lots of pressure in the reservoir. That gives the poor shot count.  I have a little test rig with a pressure gauge that I can install the reg into and actually check and adjust the output pressure before I put the reg into the P-Rod.    I took one reg apart and ended up getting the adjustment off by an entire turn, so it is easy to get the pressure off if you are not careful, and with no gauge in the gun, it is easy to be unsure of the pressure. In the tuning process, I put 2 red reference dots with a Sharpie on the end of the reg: one on the brass adjuster, and one on the aluminum body.  That way, when I removed the fill nipple adapter from the front of the gun, I could use a flash light to see where the setting was.  Then I would use a long screwdriver to make fine adjustments without having to take the reg out of the gun.   But you need the reference dots to show how much of an adjustment you are making.  Approx 1500 psi per full turn, clockwise decreases the pressure.

One approach to tuning:
Using my final string as an example, think of it this way:   
The goal was 750 fps with a 14.5 gn pellet.  Without a reg in the gun, the lowest pressure I could tune the gun to and get a flat string of a 4 shots and still maintain decent air efficiency, was between 1740 and 1600 psi.  It's a paradigm shift in thinking: don't worry about what the gun is doing at 3000 or 2000 psi, just find out what it does at the low, ending pressure.  So, knowing that the gun works well at 1740 to 1600, you set the reg to 1740.  Then, when you fill the gun, all the way from 3000 down to 1740, the gun thinks it has 1740 psi in it, and it shoot s great.  Then it falls off the reg at 1740, but you have already tuned it to keep shooting good down to 1600, so you are able to sneak in a few extra freebie shots after it falls off the reg.

Tuning with a reg has been described in many different ways, and this is just a different  description  of the same process.  I think the trick is finding a description that makes sense to you.   Like I said earlier,  I found the learning curve very steep, but once it clicked in my head and the light bulb went on, it all made sense.  Until it makes sense, it is difficult.

Geoff, I hope this helps some.  The Huma is a WONDERFUL regulator and once you figure it out, you will not want to part with it!
Lloyd

EDIT:
Darn, I just re-read nervoustrigger's last post and see that Geoff DOES have the pressure gauge block in there.  That doesn't change anything that I said, but it does end up wasting about 9 ccs of HPA volume.
Lloyd

[Geoff]

thank you Lloyd and everyone.

I will take the advice given and go at it again.  I do like the ES it gives and the MROD would really love one

[MDStroup]

20140228_174227_zps904efea1 by Michael Stroup, on Flickr

It sounds like you may want to do something like this. Not exact, but same general direction.

[Geoff]

looks nice Michael, however I don't want to bottle it if I can avoid it.



a new issue ....

I set the reg to 1600psi and left the gauge block and gauge in to ensure I was set to 1600 and it was close to the FPE I wanted, so I pulled the gauge block and slid the plenum snug to the valve and slid the huma in

well, it wont fire a pellet ... not enough air is coming out to push a pellet down the barrel.   without a pellet the sounds is more of a pffflatt sound than a pop ... I checked the instructions from huma and w/o the gauge block you slide in the provided plenum and shoot.  sounds good to me however it doesn't move a pellet out of the barrel.


how can just removing the gauge block cause such a drastic change ?  I made no changes to preload or stroke.   

any thoughts ?