The lubricator works by displacement close the bottom cock open the top cock to fill with cylinder oil or tallow in the old days. Then close the top cock and open the bottom cock, this allows steam to enter the oiler as it condensates the water makes its way to the bottom of the tallow cup and the oil floats on top, inside the oiler will be a tube just like a wick feed oil cup as the steam condensates the rising oil makes its way into this tube oil being heaver than steam drips onto the piston or valve. you can not tell when this oiler is empty, not all tallow cup oilers have the center tube. Do a Google search for tallow cup lubricator/ oiler Adam