100 psi pressure drop at top of fill?

[wahoowad]

I charge my Marauder to 2700 psi but notice I actually have to fill to 2800 because it drops down about 75 to 100 psi right after reaching 2800. Its like it settles in to 2700 but then doesn't drop any further. Here's the actual steps:

• Connect to tank and slowly fill from 2000 psi to 2800 psi (about 10 seconds to fill)
• Turn off air and I see it drop down about 75 to 100 psi and stop
• Release hose pressure

I use this regulator but don't normally touch the adjustment knobs as it is set to only fill to 2800. I don't hear any air being lost, it's like it is just equalizing or something. There is no regulator inside the gun. Again, it just drops that 100 psi and stops. Then works normally as I shoot. I have the regulator on my tank as I often shoot tethered, and also use different pressures with different PCPs.

[Geoff]

taking a guess here


gets hot filling then cools down ?

[scrane]

Good guess!

[PlanB]

i think they all do it.

[screwwork]

Nobody else said it so I will, nice tank & pressure reg setup

[Charles Outdoors]

Sounds normal to me. I always have to go over a little to get it to settle to the PSI I want.

[rsterne]

Yep, normal to lose about 100 psi on cooling....

Bob

[wahoowad]

So this 'cooling' occurs immediately, like within a couple seconds and I drop 75 psi?

[Ribbonstone]

Pretty fast  Air gets hot from compression, but it has a kind of large metal surface area (air tube) to conduct/transfer the heat.

Ball park number would be 5 PSI per degree of change (actually, it's something between 5 and 6psi, but we're just talking "do it in your head" type figuring rather than working through the gas laws).

[anuthabubba]

On my first Daystate in '90, the 'experienced guys' instructed me to refill it slowly, over at least a minute and a half, to help reduce pressure loss (shot consistency) due to heating/cooling.

This comes to mind every time I read of guys being able to fill their SCBA tanks, with their compressors, in just a couple minutes.

[Ribbonstone]

Few tank fillers seem to be willing to wait a whole minute for a fill...tanks breed impatience.
Think most just overshoot a bit and hope it cools down to what they wanted.

[marty2]

All my PCP rifles do it. I leave everything hooked up for a little until the pressure stabilizes then slowly bring up the pressure  to  the desired level.