Back in January, I wrote a blog story about carbon fiber tanks, hoses, fittings, and adapters. That story got into the equipment, and some of the various pieces of gear involved with filling PCP (Pre-Charged Pneumatic) airguns.
One other small piece of equipment, that I didn't mention in the previous story, but is very useful, is an item called a "Dead Head." This is a small fitting with a male Foster on one end, and a plug on the other. (See above picture) It essentially seals the end of the fill hose, where either a fill adapter, or an airgun like the Marauder would normally connect.
Normally, when filling your PCP, the gauge on the tank is reading the pressure in the gun as you fill it. If we replace the PCP on the end of the fill hose, with a "Dead Head" and open the main valve, the gauge will now be reading the pressure in the hose.
Since the proper high pressure hose for this application, is rated for much higher operating pressures than a PCP's air tube, or even the 4500 psi in a full 4500 psi carbon fiber tank, we can now open the valve on the 4500 psi carbon fiber tank all of the way, it will fill the hose to the highest pressure left in the tank, and the gauge will indicate that pressure. You now know how much air pressure is left in your tank.
To safely remove the "Dead Head" from the fill hose, the hose must first be bled of the high pressure air that was left in it, when the main control valve was closed. That is done by using the bleed valve that is located next to the main control valve. It is now safe to remove the "Dead Head" from the end of the fill hose.
The remaining pressure left in your carbon fiber tank, is very useful information to have at your finger tips. Nothing like getting into a lengthy pellet testing project for example, only to discover that all you have left air wise, is a couple of full pressure fills remaining in your tank.
As can be seen in the picture above, this tank's remaining pressure is down to 3300 psi. Since I fill most of my guns to 3000 psi, or there about, it's getting close to the time, to go and see my friendly neighborhood Dive Shop for a fresh 4500 psi fill.
I purchased my "Dead Head" from Mac1 Airguns for $14, a real bargain. It gives me a convenient, inexpensive way to quickly check the remaining air pressure in my carbon fiber tanks.