_l._ All minor parts exposed to the action of water in water cylinder, that are not herein specified, must be of brass, bronze, or other non-corrosive material. 31. PUMP VALVES. _a._ All the suction and discharge valves in any one pump must be of the same size and interchangeable. _b._ There must be a clear space around each rubber valve, between it and the nearest valve, equal to at least one-fourth of the diameter of the valve, or between it and the wall of the chamber of at least one-eighth of the diameter of the valve. _c._ These valves must be of the very best quality of rubber, of medium temper, with a face as soft as good wearing quality will permit. They must be double-faced, so they can be reversed when one face is worn. The quality of rubber is almost impossible of determination by brief inspection or by chemical analysis. The relative amount of pure gum and of cheaper composition may vary, or good material may be injured by defective vulcanization. The only safe way to secure excellence and uniformity is for the pump manufacturer to test samples of each new lot under severe duty (as by a week’s run in a small special pump, with say 150 pounds pressure and heavy water hammer, or by some equivalent means) and to furthermore require the rubber manufacturer to mould a date mark as “(Name of pump manufacturer, lot 201—April 3, 1904.)” on the edge of every valve, by which the pump manufacturer can keep track of those which prove defective. 32. SIZE AND NUMBER OF PUMP VALVES. _a._ The diameter of the disc of rubber forming the valve must not be greater than 4 inches or less than 3 inches. Three and a half inches diameter is probably the most favorable size, but is not insisted upon. There is some confusion between different shops about designating size of valves. The practice is here adopted, which is much the most widely used, of naming the diameter of the disc of rubber which covers the ports, and it is hereby specified that this shall be about 1/2-inch greater than the diameter of the valve-port circle which it covers, thus affording about 1/4-inch overlap or bearing for the rubber disc all around its edge. If valves are larger than 4-inch there is an increased tendency to valve-slam at the very high speed at which the pump is designed to run, and if valves are smaller than 3 inches diameter the greater number tends to unnecessary multiplication of parts, and the ports being so small are a little more liable to become obstructed by rubbish. _b._ The thickness of the rubber valve must in no cases be less than 5/8-inch. 33. SUCTION VALVE AREA. _a._ The total lift of suction valves must not exceed 1/2-inch. _b._ The net suction valve port area and the total suction valve outlet area under valves lifted 1/2 inch high must not be smaller than the figures given in the table below.