PIPES AND NOZZLES.	179
	an attachment is required, cast-iron gates being placed on each branch. The annexed sketch (Fig. 32) shows the form of these gates used in the mines, and also as a dis­charge gate for reservoirs. Where several branch pipes are supplied from the same main pipe they are usually of smaller diameter.
	Their use arises from the greater convenience of moving the smaller pipes. They are generally 11 and 15 inches in diameter. It is recommended, however, in order to prevent a loss of head, to continue the branch pipes of the same size as the feed pipe, and to regulate the dis­charge by the size of the nozzles. At the Southern Gross and Polar Star Mines the supply pipes at the pressure box are 40 inches and 48 inches (respectively) in diameter, tapering for 500 feet to 22 inches, which size they retain for 2,800 feet, then branching into two pipes each of 15 inches. At the Malakoff the pipe at the head is 27 inches, narrow-