A perimeter wall lubrication system for molten metal molds wherein the lubricant conduit within the permeable perimeter wall is configured with a K constant which is lower than 40 or more in the equation where X is the perimeter of the groove in the permeable perimeter wall and Y is the perimeter to area ratio, relative to the equation k=XY in a plot of the respective values. Electrochemical gas sensors usually comprise an external housing, which acts as a reservoir for electrolyte; a wick to keep electrodes wetted with the electrolyte and external electrical terminals, for making electrical contact with the electrodes. The pump module generally includes a chambered block, a piston drive assembly having a piston, a first motor mechanically coupled to the piston drive assembly for rotating the piston and a second motor mechanically coupled to the piston drive assembly for axially translating the piston.