Canadian Airgun Forum

So I have my regulator working. Nice 10 fps ES over 30 shots. However 37 shots was all I got from a 200 bar fill. When the reg wasn't working I got double that with a greater fps avg. Wassup ?
Heres what I assumed. I lowered the reg output to 1200 pounds thinking that is plenty for the 800 fps I was seeking, and so should get over 50 shots. I started with 825 fps then for the first 7 shots slowly dropped to 776 fps then hovered around 785 for the remainder of 37 shots down to 60 bar. The stand off is at factory length set for 920 fps. I think I might be wasting air with the volume of the stand off and valve.
Robert Lane suggested in one of his videos that the air travels behind the pellet in a ball instead of expanding and pushing the pellet as it expands. Therefore higher pressure regulated puffs of air but at less volume should push the pellet faster, instead of larger puffs of low volume air. In another one of his videos he provides a chart to calculate the correct size of the stand off and pressure for optimum air useage, but I can't make heads or tails of it.
I guess what I'm asking is..... do I need more pressure and less volume or just less volume, or what ???

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If I had only one wish, it would be to be able to "unsay" things.

No idea how much volume your standoff and regulator displace but that may account for the shot count drop as that volume is no longer pressurized.
edit: The standoff (contents) also displaces higher pressure reservoir air, so displaced volume and potential loss from the regulated plenum volume lost for holding 200bar.

What is a standoff?

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Walter

The bit between the valve and regulator that provides regulated plenum volume.

What is the pellet weight?.... Are we talking a standard AT-44 (short reservoir, which is 180 cc)?.... What is the total length of the regulator and standoff (ie how much of the reservoir have you lost)?....

Given that information I can calculate the efficiency you are getting and obtain some idea if your expectations were realistic, or if your results are about as good as you can expect....

Robert Lane's comment about the air "travelling in a ball" leaves me totally confused, but he is correct that small high pressure puffs of air are more efficient than a longer push using lower pressure air.... Unfortunately, that is exactly what you get with a regulator, a longer push using lower pressure air (compared to the full 200 bar you start with without the regulator).... Instead of starting with 2900 psi and shooting down to maybe 1500-1700, you are working with 1200 psi, so you have reduced the efficiency of the gun by quite a lot....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

so are you saying I should re set the reg back up ?
the gun is the 180 cc at44 and the pellet is 14.3 gr jsb. Shot count from 200 bar down to 60 bar 37. Avg speed 785 fps. The reg is about 1.5 cubic inches. 1.25 inches long by whatever the dia of the tube, plus a 1 inch by .5 inch piece projecting from the main body of the reg.

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If I had only one wish, it would be to be able to "unsay" things.

hmmmmmmmmm.... don't quite know what that means.... is that projecting up into the reservoir or down into the plenum?.....

What about the standoff.... How long is it?.... is it tubing?.... wall thickness or ID and OD?.... I need to know the total length from the valve face to the front (high pressure side) of the regulator....

The Hatsan tube is about 1" ID, so if the reg. is 1.25" long, that is indeed 1 cu.in. plus the projection (which I assume is inside the reservoir) which is another 0.2 cu.in. for a total of 1.2 cu.in. = 19.7 cc.... So now your reservoir is down to 160 cc, minus the volume of the plenum where the standoff is.... If I assume that is another inch in length, that is another 0.8 cu.in. (13 cc) so now you are down to a reservoir of 147 cc (9 CI)....

You are shooting 37 shots at an average speed of 785 fps with 14.3 gr. pellets, which is 19.6 FPE x 37 = 724 FPE total....

Your pressure is dropping from 200 bar to 60 = 140 bar x 9 CI = 1260 CI of air used.... However, 1200 psi, which is what you say your reg. is set for is 83 bar, not 60, so that is confusing....

Therefore your efficiency is 724 / 1260 = 0.57 FPE/CI, which to put it bluntly, sucks.... Even if you are stopping the string at 1200 psi (83 bar), you are using 117 bar x 9 CI = 1053 CI and getting an efficiency of 724 / 1053 = 0.69 FPE/CI which is still pretty dismal....

I suspect that unless you have backed the hammer spring preload wayyyyyyyyyyyyyy down to compensate for using 1200 psi instead of 2900, you are blowing about half the air out the end of the barrel after the pellet has left.... Try backing off the hammer strike, and keep track of the velocity, and I'm betting you will back it off (ie turn it in clockwise) several turns before the velocity drops.... When you begin to see a velocity drop, then shoot another string....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

You are almost exactly right on your assumptions re measurements. the stand off is about 1/16" thick tube wall,and 1.25" long. As for your hammer spring suggestion. I had it out 2 turns at first and got only a 20 fps increase when I turned it out 2 more turns.
I worked on the reg this morning and now have it set for 1600 psi and put a opprox. 3/4 ci plug in the stand off. of course I'll try it with and without the plug, but for now it,s with. I have not tried it in the gun yet. Will do in an hour or so.
As per your confusion
Although the reg was set for 1100, not 1200 as I stated before. Eyes bad you know. I shot below reg pressure to 60 bar. The last 2 or 3 shots falling in speed pretty fast.

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If I had only one wish, it would be to be able to "unsay" things.

That is another indication that your hammer strike is likely too much for good efficiency.... When a regulated PCP is tuned on the "knee" of the curve, it will shoot 100-200 psi below the setpoint with little or no velocity loss.... in fact the velocity may increase a few fps before falling off.... If it is tuned with even less hammer strike (for that setpoint pressure) the velocity will increase significantly and then fall off....

Your plenum, at 12 cc is NOT too large for a 20 FPE gun.... if anything it could be larger....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Well here is what I did today and the results. I went back to 12 spring washers, but changed the configuration. ()()(())(()).Then I turned out the adjustment screw on the reg,1/2 turn. I ended up with 1600 psi on the out put side of the reg. Then I put a 3/4 cubic inch plug in the stand off. Then I put my modified valve from another tube on the regged tube. (my modified valve is just a slightly heavier spring and a "sail" and the teflon plug replaced by a threaded plug, for adjusting valve spring pressure.) So I filled to 3000 psi with the hammer spring screw all the way in. using 14.6 gr jsb The first shot was high at 783, but the rest were between 743 and 773. out of 20 shots 16 were between 760 and 767. The next 20 shots were with 13.43 gr jsb. they were between 787 and 803 only 3 were over 800 fps. then 20 more using 18.1 gr they were from 702 to 720. the regulator then spiked to 731 and slowly declined to 702 for a total of 82 shots and 70 bar still in the gun.
So the reg is now working perfectly. However. I wanted to achieve a goal of 800 fps. So I turned the hammer out 2 turns and shot a complete string using only 15.6 gr jsb the results were "for me" perfect. First shot at 3000 psi was 795 fps highest speed was 814 but that was when the pressure dropped below reg pressure at shot number47. the last shot was at 777fps and the air left was 90 bar Total shots was 55 and 45 or so were between 798 and 806. point of impact varied only 1" up and down for the entire string except the last 2 shots. I was going to test it with the plug out of the stand off but I'm not sure I can get better results. 55 shots at an avg of 800 fps sounds nice to me. What do you think Bob ?

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If I had only one wish, it would be to be able to "unsay" things.

Looking good Joe!

try without the displacer plug as the valve will see more closing force if there is more air available

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Walter

I agree, you should get a bit more velocity as well, as you will have a higher average pressure during the shot.... It that is more power than you want, you can turn the preload in (less hammer strike) to get the velocity back to what you want with more efficiency....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

OK I'll giv it t try tomorrow. What is my efficency now Bob ?

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If I had only one wish, it would be to be able to "unsay" things.

If I use a velocity of 802 fps and 15.6 gr, that is 22.3 FPE x 55 shots = 1226 FPE....

You used 110 bar x 9 CI = 990 CI of air.... so the efficiency is 1226 / 990 = 1.24 FPE/CI....

That's more like it !!!

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal; Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!

Thanks Bob. Now that I have your formula in a way I can understand it, I should be able to calculate myself.

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If I had only one wish, it would be to be able to "unsay" things.