So I am a heavy vehicle mechanic. One of my vehicles has an air starter with a separate air tank dedicated to the starter. This tank is fed from the main air tanks on the truck with a check valve to only allow air into the starter tank. The gauge on the dash only displays the pressure in the main tanks for the truck. We frequently notice the starter tank will have more or less pressure than the main tanks. I understand why the starter tank sometimes has more pressure than the main tank due to the one way check valve. I assume the check valve has something o do with why the starter tank might have less air than the main tanks. The check valve is a 3/4" and has a spring with probably not more than a couple of lbs. The starter tank is considerably larger than the main tanks, it that matters. My question is, why will the starter tank have less pressure than the main tanks?