Improper pipe size is a common fault of vacuum supply systems on California dairies. Data presented in this study indicate that a minimum vacuum supply pipe diameter of 1 1/4 inches is needed to handle four or five milking units and 2-inch pipe is the minimum size required for 7 to 12 units.

The authors extend their appreciation to ABRAC Inc. and to Fresno Sales, Inc., both of Fresno, for the loan of pumps and pipe fittings to make these tests possible; to A. R. Johnson, Agricultural Power Engineer, Fresno District, Pacific Gas and Electric Company; and to Archie Post, Superintendent of Fresno County Yards.