9mm Evanix Blizzard / Rainstorm tuning

[rkr]

I'm not an engineer but for better air flow shouldn't the leading and trailing edges be rounded or tapered where they are in the air stream for less turbulence of the flow ?

Indeed they should be and we should actually use NACA 0015 airfoil design as our guideline Seriously though, I'm more worried about making that piece tough enough to withstand the pounding of the valve, if it disturbs the flow I'll just drill the hole to a bigger size to fix things.

[dogwood]

That looks really good rkr have you thought about filing some grooves in it to keep the spring centered?

[rkr]

That looks really good rkr have you thought about filing some grooves in it to keep the spring centered?

In case you didn't notice the higher middle part in those copper strips goes inside the spring and centers it while the spring end sits against those lower ends.

[SeanAT]

Didn't see this thread until now. Glad that the PEEK arrived and you're making progress. 

[dogwood]

Ah, ok I see it now, scale threw me off.

Wonder if it would be worth the trouble of going to a smaller dia. Spring and get it farther out of the air flow?

[rkr]

Didn't see this thread until now. Glad that the PEEK arrived and you're making progress. 

It did Sean and it really saved the day. It is pretty tough material so it's not the best as far as sealing goes. We'll see if it will be the final seal material, I may try PET-T as well.

The valve bounce is pretty wild so I think I'll be playing with springs as well to see if I can tame it down. Right now it looks like 180 fpe could be reachable if I drill out the transfer port a bit. We'll see where this all leads to.

[SeanAT]

It is pretty tough material so it's not the best as far as sealing goes.

I really do think PEEK is the best material to use if it can be implemented properly. Its hardness requires that the two sealing surfaces be smooth and completely parallel with each other. I'm not so sure you can get a perfectly parallel face and matching stem hole without using a lathe, but maybe I underestimate your abilities  . It also helps to have the valve sealing surface as thin as possible.

As an example of successful implementation, I have a PEEK valve stem in a Crosman 600 that seals perfectly under only CO2 pressure. The valve face has been chamfered and the sealing lip is only about 0.5mm wide.

Again, sorry for not asking before I sent the rod, I would have made some seals on the lathe for you. 

[rkr]

The PEEK did seal on my first assembly with valve spring but when I took the spring out it started leaking. Today I was supposed to lap the seal against the seat but somehow I ended up drilling the transfer port to 7mm size 

[rkr]

Well, then - I think the problem was that the seal was a bit too thin and the seat was touching the metallic rim around the seal as it compressed. So, I made a new thicker seal and put the gun back together for some testing:

200 bar, 5.7 gram bullets:

930 fps - 169 fpe
929 fps
911 fps
889 fps
875 fps
--- 150 bar

This is starting to look rather good, to get to 170 fpe level with these light bullets is not bad at all. I think I need to try some heavier bullets next.

[rkr]

Heavy bullet test:
200 bar, 134 grain bullets
785 fps - 183 fpe
783
770
758
702
--- 150 bar

Nice power but I was really looking for a flat string of 5 shots, shot number five really ruins it. Maybe I should fill to 210 bar...

I think I'm done with power mods now. I may fix another valve for the gun since I doubt the stock one will last forever but that should be it. Next it's time to flatten that shot string and find another tune level for light pellets/JSBs/round balls.

[rkr]

Tune for lighter pellets could take some time, this is 200 bar string using .360 roundballs with the spring preload all backed out (factory settings):

946 fps
953 fps
953 fps 135fpe
938 fps
928 fps

Goes to show mow much the airflow has increased. I need to start looking for weaker and/or shorter springs now, way too much dwell for this purpose. I was hoping to get around 860-880 fps.

[wwonka]

The 180 FPE tune is v. nice.  So the Rainstorm/Blizzard officially joins the ranks of that power level.

It would make a really versatile gun to be able to bring it up to 180 FPE and shoot 134 grains for fewer shots, or lighten the spring and shoot roundball or JSBs for 130 FPE with longer shot strings.

As you know, the springs are super easy to swap. I've had some good results swapping springs out of my .22 Rainstorm for very quick and dramatic power/shot string changes (in about 5 minutes). NomadicPirate did this too, and there's a thread you may have already seen on Rainstorm spring replacements...
http://www.gatewaytoairguns.org/GTA/index.php?topic=58511.0

Here's also a good link to predict the force of different springs, in case you're shopping:
http://www.efunda.com/designstandards/springs/spring_calculators.cfm

[rkr]

One of the local chaps made me a nice new valve from PET-P material. Here's a shotstring I got:

---200 bar, hammer spring at stock settings, .360 roundballs
925 fps
946 fps
954 fps
958 fps
954 fps
---155 bar
930 fps
917 fps
---140 bar - one magazine
889 fps
871 fps
844 fps
---110 bar

So it seems that there's no practical difference in these two seal material. The PEEK string in previous post looks like it would start at lower fill pressure, (which indeed might have been the case - human error) other than that the results are pretty much identical. The string itself gives some hope, if I lower the speed to 860-880 fps range and get rid of the hammer bounce I might well get 15 useful shots / fill ór two full magazines which would be great. To be continued.

[SeanAT]

Just keep an eye on compression set of PET over time. My guess is that there will quite a bit more than with the PEEK.

[rkr]

I've been working with low power tune lately and finally got some results, not perfect but getting there.

First let's take a typical shotstring from wwonka's post:

78 gr:
1. 820
2. 822
3. 807
4. 802
5. 804
6. 786
7. 771
- Peak FPE above is 116 FPE.

As we can see that's 7 decent shots.

Then let's have a look at my previous long shot string after some basic tuning:

200 bar with JSBs
822 fps (first shot after tune, I guess it's OK to be low)
860 fps
870 fps
865 fps
862 fps
866 fps
866 fps
840 fps
827 fps
816 fps
130 bar

10 good shots topping at 129 fpe.

Finally the shot string from today, two magazines worth JSBs from 200 bar fill:

--- 200 bar
860 fps
862 fps
864 fps
881 fps
889 fps
---165 bar
894 fps
904 fps - 140 fpe
899 fps
888 fps
876 fps
---140bar
858 fps
850 fps
831 fps
808 fps
---115 bar

So, I get 12 rather good shots now and by some fine tuning of the valve springs I believe I can strecth it out to 14 which is my goal. The power goal was 120 fpe so I'm still well over that which gives me room for experimentation. This also shows how much the air efficiency of the gun has improved from the stock gun by just doing some rather trivial changes. I also managed to reduce the hammer bounce to one extra valve opening, not perfect but it shows in that shot string.

[Nomadic Pirate]

That's an impressive string

[wwonka]

V. impressive improvement in overall performance. Nice shift upwards in power and at the same time stretching out of string.

Did you make any changes in tuning between this string and the .360 roundball string above? The spring was backed all the way out for that string - so did you swap the hammer spring? or tweak the valve spring between the two strings?

[rkr]

I changed the stock hammer spring to a short and somewhat stiff two spring setup. It doesn't preload the hammer at all, rather there's a 2mm or so gap where the hammer moves freely towards the valve. With this system the roundballs were flying at 915 fps. I believe the 9mm inlet in the valve housing is again restricting the airflow, I guess I need to drill it to 10mm size next.

[rkr]

Another low power string with depinger and some more tuning changes:



14 shots starting at 116 fpe, going to 136 fpe and back to 116 fpe. For 7 shots I could fill to 180 bar and get 12 fps variation.

The curve still is a bit peaky and I can't really figure out why, any tuners there to spot what's wrong?

The new version of the depinger is great, makes the gun much nicer to shoot when there's just thump instead of that long twang.

[wwonka]

The curve still is a bit peaky and I can't really figure out why, any tuners there to spot what's wrong?

Once you open up the ports in a PCP, you will often see greater peakiness in the power curve - this appears to be one of the common tradeoff side-effects.

I've seen some people go back and reduce the port opening for low power configuration, and increase it back for high power - using types of valves that allow that type of opening and closing.

But I think the curve you have here (with 116 FPE up to 136 FPE going back down to 116 FPE) in two full magazines is a pretty extraordinary improvement over the stock shot strings of this gun, and pretty far from where you started