Designed to pump oil into the system while the unit is operating without shutting down for charging. Smoothly pumps oil into the compressor on the down stroke while system is under pressure, resulting in easier pumping on the positive stroke. The universal tapered rubber adapter is designed to fit all 1, 2-1/2 and 5 gallon containers without additional adapters. Works against 200 psi of pressure and is compatible with all oil types including synthetic, mineral and polyol ester. Pumps 2.6 ounces (78 ml) per stroke.