GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: perazzisc3 on December 03, 2019, 10:20:40 PM
-
Fx Crown with the Amp regulator creeps down from 138 to just above 130 bar.
What might be the issue?
-
Is this from a full fill? And it creeps down as your shooting? When you shoot regulated plenum pressure drops, then builds back up to 138 bar , then creeps down to 130 again?
-
I think Jacob is asking the right questions. We need to differentiate between the regulator’s input regulation versus some other cause. Which scenario is it?
Scenario 1: You fill the reservoir and take a few shots and notice the plenum is at 138 bar. Later, as the reservoir is nearing the point where you need to fill it again, you notice the plenum is only at 130 bar.
[This would indicate the regulator has poor input regulation.]
Scenario 2: You take a shot and check the plenum gauge and watch it climb to 138 bar. Then you wait some time and the gauge declines to 130bar.
[This would indicate that the plenum has a leak. At some point the regulator will respond to the drop in pressure and its valve seat will open again to top off the plenum, but it may not top it off to the same pressure as it does right after a shot. This difference has to do with how the regulator responds to a rapid drop in pressure (a shot) versus a gradual drop in pressure (a slow leak).]
Or do neither of these adequately describe what you’re seeing?
Another related question, what’s the average velocity you’re getting at 138 bar versus what you get at 130 bar? A 6% pressure delta should not make a meaningful difference if the tune is adjusted well.
-
I think Jacob is asking the right questions. We need to differentiate between the regulator’s input regulation versus some other cause. Which scenario is it?
Scenario 1: You fill the reservoir and take a few shots and notice the plenum is at 138 bar. Later, as the reservoir is nearing the point where you need to fill it again, you notice the plenum is only at 130 bar.
[This would indicate the regulator has poor input regulation.]
Scenario 2: You take a shot and check the plenum gauge and watch it climb to 138 bar. Then you wait some time and the gauge declines to 130bar.
[This would indicate that the plenum has a leak. At some point the regulator will respond to the drop in pressure and its valve seat will open again to top off the plenum, but it may not top it off to the same pressure as it does right after a shot. This difference has to do with how the regulator responds to a rapid drop in pressure (a shot) versus a gradual drop in pressure (a slow leak).]
Or do neither of these adequately describe what you’re seeing?
Another related question, what’s the average velocity you’re getting at 138 bar versus what you get at 130 bar? A 6% pressure delta should not make a meaningful difference if the tune is adjusted well.
Scenario 2 appears close to what I am experiencing, velocity also drops.
-
sent my wildcat mkII back for warranty repair that had somewhat both Scenario's
you have mentioned.
i paid the difference to have a Huma HP installed
and have never looked back............ 8)
-
Scenario 2 appears close to what I am experiencing, velocity also drops.
I presume since you didn't mention it, you haven't noticed the bottle losing pressure when the gun sits unused for a few days? To be clear, I'm referring to the bottle/high pressure reservoir this time, not the plenum.
Please note regulator creep refers to the tendency for air to slowly weep through microscopic imperfections in the mating surfaces of the valve seat. This means high pressure from the reservoir slowly migrating to the plenum, thus the only direction for the plenum to go is up.
In this case, it's going down. That is not creep in the technical sense but I can appreciate it being a useful term to describe, oh let's say, "a slow and undesirable change in the operating pressure". But in order for it to go down, the plenum has to be losing air. In other words, a small leak exists somewhere. Or a temperature drop of about 17°C (30°F) would have the same effect. In either case, at some point the plenum pressure will fall enough that the valve seat will open and air will flow in to top it off. Note there may be some observable hysteresis, meaning the plenum may have to drop a few bar before the valve seat opens, but what I was attempting to describe in the previous post was that this new topping off pressure may not be the same as what it rose to after a shot because of the dynamics of the pressure drop being relatively slow.
Regarding the loss of velocity when the pressure falls, that says the hammer strike is adjusted too strongly. If you back it off a little, the rifle will be more forgiving of slight variations in pressure. 8 bar (116 psi) is actually a very small delta if you were testing and tuning an unregulated PCP. For example it's not uncommon to get a 2% ES over a span of 500psi with a well-tuned conventional PCP. So the way you'd go about adjusting your regulated PCP is to dial up the hammer spring tension until you find the maximum velocity it will achieve. Then simply dial it back until the velocity drops to 95% - 97% of that maximum. So let's say you find the max to be 900fps, you'd back off until you hit 900 * 0.97 = 873fps or so.
-
Scenario 2 appears close to what I am experiencing, velocity also drops.
I presume since you didn't mention it, you haven't noticed the bottle losing pressure when the gun sits unused for a few days? To be clear, I'm referring to the bottle/high pressure reservoir this time, not the plenum.
Please note regulator creep refers to the tendency for air to slowly weep through microscopic imperfections in the mating surfaces of the valve seat. This means high pressure from the reservoir slowly migrating to the plenum, thus the only direction for the plenum to go is up.
In this case, it's going down. That is not creep in the technical sense but I can appreciate it being a useful term to describe, oh let's say, "a slow and undesirable change in the operating pressure". But in order for it to go down, the plenum has to be losing air. In other words, a small leak exists somewhere. Or a temperature drop of about 17°C (30°F) would have the same effect. In either case, at some point the plenum pressure will fall enough that the valve seat will open and air will flow in to top it off. Note there may be some observable hysteresis, meaning the plenum may have to drop a few bar before the valve seat opens, but what I was attempting to describe in the previous post was that this new topping off pressure may not be the same as what it rose to after a shot because of the dynamics of the pressure drop being relatively slow.
Regarding the loss of velocity when the pressure falls, that says the hammer strike is adjusted too strongly. If you back it off a little, the rifle will be more forgiving of slight variations in pressure. 8 bar (116 psi) is actually a very small delta if you were testing and tuning an unregulated PCP. For example it's not uncommon to get a 2% ES over a span of 500psi with a well-tuned conventional PCP. So the way you'd go about adjusting your regulated PCP is to dial up the hammer spring tension until you find the maximum velocity it will achieve. Then simply dial it back until the velocity drops to 95% - 97% of that maximum. So let's say you find the max to be 900fps, you'd back off until you hit 900 * 0.97 = 873fps or so.
Excellent information!
I am not aware of pressure loss from the CF bottle it might be very little and I haven't noticed.
You have given me a lot to look out for.
Thank you VERY much.
-
Good luck! Let us know how it goes.