Table of Pumps for Airguns

Since I now have a pressure gauge I thought I might as well do my own table for my Seac Hunter 90 and it was quite surprising. Basically, it takes a lot more pumping than the Asso table says. I can't find a table for the Hunter, but I thought the Asso and Hunter were basically the same gun - the Hunter being a face lifted one with a new handle (and a 2mm trigger pin).
But here it goes, according to my measurements:

100 pumps: 4 bar
200 pumps: 8 bar
300 pumps: 11.5 bar
400 pumps: 15 bar

I will edit this post later, as I put more air in it.

Diving Gecko said:

Since I now have a pressure gauge I thought I might as well do my own table for my Seac Hunter 90 and it was quite surprising. Basically, it takes a lot more pumping than the Asso table says. I can't find a table for the Hunter, but I thought the Asso and Hunter were basically the same gun - the Hunter being a face lifted one with a new handle (and a 2mm trigger pin).
But here it goes, according to my measurements:

100 pumps: 4 bar
200 pumps: 8 bar
300 pumps: 11.5 bar
400 pumps: 15 bar

I will edit this post later, as I put more air in it.

Click to expand...

Air lost from the "dead space" at the bottom of the hand pump where it connects to the gun represents an increasingly larger volume (at atmospheric pressure) of air as higher pressures are being reached in the pneumatic gun. So that is why you need more pump strokes for higher pressure increments than you need for the same increments at lower pressure because some of the air, which you have compressed in the pump, escapes when you pull the pump handle back up. The spatial volume lost is the same each time, but at increasing pressure that volume contains more air molecules which expand to represent a greater loss of air from the pump.

Another variable is the pump itself, some individual hand pumps seem to be better than others, probably due to small leaks at either the connection to the gun or at the plunger seal itself and the quality of the pump bore surface. As the air pressure in the gun reaches higher levels the pump gets progressively hotter at the lower end due to adiabatic heating of the compressed air, so the air pressure being transferred is higher than it would be if the pump stayed cool. The effects are small, but they result in different pressures for a given number of pump strokes, so the numbers in the official tables are a guide. When you use a gauge you actually let some pressurized air out, unless the gauge monitors the pressure as the air is going in and the gauge taps into a connecting manifold with its own control valve (that way the pressure gauge needle does not swing completely around with each pump stroke).