Others Benjamin Manometer Reading

[Ezana4CE]

Has anyone else noticed or experienced issues with Benjamin manometers not reading reservoir pressure accurately? I’ve noticed on multiple Bulldogs and a Marauder pistol that when filling the reservoir to 3000 psi, the manometer will stop at 3000 psi, then drop down to 2800-2900 psi. Anyone else notice this? What could be the cause of this? Is there some sort of failsafe built in to prevent over filling or does it sound like these manometers are in need of replacement? If they are in need of replacement, what’s a reliable and accurate replacement manometer?

 

[hameditor]

Hopefully @BenjeneerJohn will reply to you on this topic for an official answer.

However air pressure in a newly-filled PCP gun always tends to fall a little after filling as the temperature of the filled air drops,reducing the pressure. Could this be the cause for what you are experiencing?

Generally there's no overfill protection in PCPs although some Air Venturi Avenger models include burst disks to prevent catastrophic overfilling.

 

[Ezana4CE]

@hameditor What’s perplexing about it is this: I’ve read of people over pressurizing the reservoir of a pistol and having to degass it because over pressurizing the reservoir causes valve lock by creating more pressure on the opposite of the cable to where the hammer strike is not powerful enough to crack the valve open. I’ve intentionally tried to push the pressure a little beyond 3000psi on my Prod to see if I could get the manometer to settle on 3000 psi. The result was that I could never get it to over pressurized (reading beyond 3000 psi) and I didn’t want to intentionally push it too hard (to 3500-4000 psi), so I didn’t push it that far. I’ve done similar things with my Bulldogs. On the Bulldog the manometer would read over 3000psi then drop down to 2800-2900. It does this if I’m outside shooting and have been out there a while where temps would be pretty even in the SCBA tank and gun having been in the outside ambient air for an hour or more. I can’t figure this one out.

 

[BenjeneerJohn]

If I am understanding correctly, you fill the rifle to 3k. Then after a little bit the pressure drops to 2800-2900? If that is the case that is what happens as the pressure tube cools. When you fill the pressure tube, it heats up. The pressure increases with temperature. Then as the tube cools, the pressure drops a little bit.

John

 

[Ezana4CE]

If I am understanding correctly, you fill the rifle to 3k. Then after a little bit the pressure drops to 2800-2900? If that is the case that is what happens as the pressure tube cools. When you fill the pressure tube, it heats up. The pressure increases with temperature. Then as the tube cools, the pressure drops a little bit.

John

@BenjeneerJohn It does this regardless of whether I top it off fast or slow or if I allow the manometer to settle and pressure to drop a little and then try to top off from 2800 to 3000 psi. These manometers do not register 3000 psi. They will drop when I close the tank valve before disconnecting the fill whip. The guns' reservoirs don't have to have time to cool off. I have done all that I can in attempt to avoid blatantly over pressurize the reservoirs well beyond the recommended fill pressure. Aside from doing so, I'm not confident that these manometers are reading pressure correctly, especially on the small Prod reservoir. Something isn't adding up here. The common factors in these equations that do not change are myself, the guns, their reservoirs, my SCBA tank and valve, and the manometers.

 

[Ezana4CE]

Anyone know of any replacement manometers that can be used?

 

[BenjeneerJohn]

Are you saying you can watch the gauge on your air gun drop when you open the bleed on your tank? Do you open the bleed fast or slow? if slow, some air might be coming back out of the rifle before the check valve closes. I try to open the bleed valve as quickly as I can to dump the air line.

I have not seen this issue before. I am not sure what the issue is.

 

[Ezana4CE]

Are you saying you can watch the gauge on your air gun drop when you open the bleed on your tank?

@BenjeneerJohn That is precisely what I'm saying. It almost looks like some sort of internal spring resistance. I am in the habit of bleeding my fill whips quickly. I just unscrew the relief valve on the side of my SCBA tank valve and the air exits rapidly in a quick hiss. Then I remove the female foster quick connect from my gun's fill nipple.

 

[BenjeneerJohn]

That is interesting. It seems like the check valve is not closing quick enough.