The waste pipe can pass down to floor between the yokes at middle of pump. It should be piped in such a way that steam and gases from other drains or waste pipes will not work back through it, and, by being troublesome in the pump room, suggest the covering of the cone in any way, as it is desirable that the pump operator should always be able to see instantly any waste from the relief valve or air vent. This cast-iron cone, connected to the safety valve and air vent, is included in price of pump, but the waste pipe beyond it is not. 45. AIR VALVE. [Illustration: FIG. 13.] _a._ An air vent with a brass gate valve and brass pipe for connecting up, must be provided and connected with delivery elbow and discharge cone. _b._ The size of this air vent should be one inch for 500-gallon and 750-gallon pumps, and one and one-fourth inches for the 1000-gallon and 1500-gallon sizes. _c._ The hand wheel of this valve must be marked as per Fig. 13. The lettering must be very open, clear and distinct, not liable to be obstructed by grease and dirt, and of a permanent character. The object of this valve is to reduce the pressure above force valves and secure a prompt riddance of all air that may come through the water cylinders when first starting up. This valve, of course, should be closed when once pump is under way, to prevent waste of water. 46. PRIMING. _a._ Each pump must be fitted with a set of brass priming pipes and valves, according to either one or the other of the following methods: _b._ For 1,000 and 1,500 gallon pumps, the priming pipes must be 1-1/4 inches. For the 500 and 750 gallon pumps, the pipes must be 1 inch. Pump-makers are to furnish these pipes and the fittings called for below, and are to connect them up providing a 2-inch outlet, looking upwards, ready for the supply from the priming tank. The pipe from the priming tank to this outlet should be at least 2-inch, and may be of iron, and is to be furnished by the purchaser. All parts furnished by the pump-maker are to be of brass, and are to be included in the price of the pump. CONTROLLABLE VALVE ARRANGEMENT. _c._ Four 2-seat controllable valves, one for each pulsation chamber, and of the general type illustrated in Fig. 14, must be provided. In these the inlet of water and outlet of air are simultaneously opened and closed by the pump operator. [Illustration: FIG. 14.] Objection has been raised to this double-seated valve from the possible difficulty of keeping both seats tight. If desired, the valve may be fitted with a flange instead of a screw connection, and the stem between the two seats somewhat enlarged and provided with a suitable spring, thus giving flexibility between the two seats and preventing all trouble from uneven wear.