vulcan .25 unstable velocity !!
Nice to be with you guys, and hope to learn more.
Three months ago, I got my .25 vulcan tactic.
I screwed the hammer spring adjuster a little bit in, and was shooting at 920 FPS.
everything was ok, but for the past two weeks I have noticed some changes. So, I checked the velocity.
Filled to 250 bars, the gun shoots at 910 FPS.
When it reached 170 bars, it dropped directly to 870 FPS.
and when it gets to 150 bars, it goes down to 840 FPS.
Refilled and done the same steps again, I will always get the same results.
Is it the regulator? shall I take it out and check the o-ring!!
What do you suggest!!
All Replies
Congratulations on managing that work.
Old regulator is black.
Did you disassemble the regulator, clean and re-lube its internal washers and check its seat? That is where I would expect the problem to be. Inside the regulator, not its external o-rings.
Thank you guys for caring and being so helpful.
guykuo…. you are absolutely right, it is a difficult and dangerous task.
HOOT…I have watched Ernest’s videos over and over since I got my vulcan. Just watched them to be aware of everything if I ended up needing to tear up my gun ( and thats what happened )
They are very helpful indeed.
I kept in mind that I may need a new regulator, but i chose to give it a shot any way. If everything went well, then I saved myself buying a new one. If not, then I will have too get a new regulator.
So, I degassed the gun and:
I thought the new vulcan has a black regulator :confusedn: … correct me if I’m wrong.
took the measurement of the regulator ( sine I have no regulator tester )
cleaned everything, tuned the regulator a bit ( made it 70.35 mm ), changed both o-rings on the regulator, re-lubed the parts and put them back in.
Finally, I filled the vulcan to 200 bars. I will let it rest for tonight to see if there is any leak or pressure lose)
Tomorrow I will shoot it to check the velocity, and surely will let you know the result.
:hoot:
Why not simply replace the regulator? Evgeny has been excellent is providing such support. Advise him of this thread and your results and lack of available service. Explain your problem reaching a dealer and ask for a replacement regulator.
De-gassing the gun is the most important step, so you won’t get hurt. Check Youtube for one of Ernest’s Vulcan take apart videos. Replacing the whole regulator is much simpler than trying to repair one, or even clean it for that matter.
However, Ernest has 13 videos on Vulcan repair. Either do a Youtube search on Ernest Rowe Vulcan, or you can jump to this video which is one of the first, the rest are listed.
Evgeny’s email: airguntechnology@gmail.com
Hoot:
I really must caution you about trying to work on the regulator yourself. It is not a trivial task. There are many steps, which we cannot guide you through via the forum. Unless, you are already experienced working inside PCP’s and handling the dangers of very high pressure air, I strongly advise you against trying this yourself. Even if you manage to get it apart safely, you still face doing proper adjustment of the regulator without the benefit of replacement components and a regulator tester. It is possible to succeed, but the odds are stacked against you and it will require multiple tear downs/rebuilds of the air cylinder to get things adjusted without a tester.
Mess this up and you can be badly injured, your gun broken further and its warranty voided.
Way your path forward carefully. We want you and your Vulcan safe.
Wow…
Thank you so much guykuo for the effort and the time you spent analyzing all these data.
The dealer I bought it from is about 400 kilometers away from me ( and he is the only one in my country )
I will try it myself before taking the long journey for the dealer.
So, I think I will try to take the gun apart and see if I can identify where the problem is and try to fix it.
And surely, I will keep you updated.
Plotted out your shot string data. Pressures between your measured values were interpolated to make the plot. I then added the red line to approximate the curve without the big random drops.
Click on below to see higher resolution graph.
This is an abnormal looking shot string. Over half of the string is off regulator. Regulated segment is not flat. There are many random velocity drops.
1. Your regulator is set to about 170 bar. The setting is a bit high, but not horrible. Ideal on the 25 is about 150 bar. You won’t be able to adjust that without a lot of work and it is very difficult without a regulator tester. This high of a regulator setting also means your hammer has to hit pretty hard to open the valve, but that is a secondary issue.
2. Regulator is poorly regulating. The “flat” portion of the curve simply is not flat. Things drop off rapidly after 170 bar. So, it is doing some regulation, but very poorly.
3. The way your “flat” portion of the curve merely curves down suggests your hammer spring tension is a little on the high side relative to the regulator/air chamber capability. It’s a bit hard to read through the noise of random velocity drops. If it is high, it isn’t horribly high. The last few shots before going off regulation seem roughly consistent.
HST too high makes the end of regulated segment slope down at end of regulation.
HST just right makes end of regulated segment remain almost flat until end of regulation.
HST low, you see the regulated segment climb and then drop after coming off regulation.
Way too much noise in the velocities to get a good handle on this.
4. The big random drops in velocity could mean hammer binding or a sticky regulator. As yours is a newer version Vulcan, it already has the low binding design hammer and spring. Because of that, I am leaning more towards a defective regulator as the cause for the big drops.
You should still inspect your hammer, hammer spring, and its silicon damping tube on your hammer spring to see if anything is binding. If it is binding, you can more readily fix that by making certain all of them are correctly positioned. Unfortunately, I don’t think this why you are seeing the drops AND poor regulation.
I would return this to the dealer for service. My prime suspect is a malfunctioning regulator. The regulator may merely need its washers replaced, cleaned or re-lubricated, but you shouldn’t need to do that on a new gun.
Thank you all for replying.
HOOT …I did reset the HST three days ago as it was from the factory.
and I believe I have shot around 900 shots, more or less , through the gun until now.
of course had cleaned the barrel several times.
guykuo…here are some numbers for you.
I tried to register 3 to 4 shots for each pressure. there are some shots that could not be read by the chorony.
I started from 240 bars :
895
889
889
at 230 bars:
865
897
904
220 bars:
900
900
909
210 bars:
874
908
909
200 bars: >>>> that is what HOOT advised to fill too
907
909
906
902
190 bars :
896
890
904
905
180 bars:
898
902
879
170 bars:
900
817
884
160 bars :
859
847
856
150 bars:
786
852
851
140 bars:
844
834
819
130 bars:
824
832
821
120 bars:
841
824
815
Can you get a full shot string with velocity and cylinder pressure numbers for us?
It’s easier to analyze if we can plot the velocity vs cylinder pressure. Read the FPS for each shot, but cylinder pressure every 3-5 shots is sufficient resolution.
The shape of the velocity vs pressure curve will help us figure this out.
:hoot:
PCP airguns have been known not to perform well with air usage at the max air cylinder pressures.
Try filling to 200 bar, shoot down to 130 bar, then check the resulting overall fps and shoot count.
The reasoning is 200 bar seems to be where a lot of pcp’s hit their max efficiency. And down to 130 bars, where the reg is likely set, after which you should see an fps drop.
Hint: Put that HST back where it was before you started getting weird results. FPS is the result of a delicate balance between the valve, the regulator, and the HST. Adjust one, and the others react, and not always as expected.
One other thought, if this is a new pcp…it make take a few fills for everything to settle down and get consistent.
Hoot:
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Thank you guykuo
In fact I did not disassemble the regulator, I guess I was either tired or stupid enough to forget to do that part 😳
I will check how does the gun do tomorrow and see if it needs another round