The sketch herewith shows a boot boiler, such as would go at the back of a range fire. All the fittings are on it, namely, safety valve (set to blow off at 5 1b. to 71b.), automatic water inlet valve with stone float, water-gauge, and the steam supply pipe that conveys the steam to the hot plate or other utensil. The water-supply valve must be fed by a water service having a water pressure in it exceeding the steam pressure named; that is, the cistern which the service comes from must be at least 18 ft. to 20 ft. above the boiler, otherwise, although the valve may open at the proper moment, no water will enter if the steam is strong enough to hold it back. When the boiler has to be recessed out of sight behind the range covings, recourse is had to a supply cistern to carry the fittings. This cistern has a steam-tight lid, and all the fittings are put on it as a rule, though some still prefer to put the safety valve on the boiler and bring it to the front by means of a short pipe. Between the boiler and the cistern are two pipes, one above and one below water level. The latter is the cold supply, while the former is an equalising pipe to prevent the steam emptying the boiler by forcing the water back into the cistern.

The steam service is taken direct to the hot plate, rising as far as it can, then (if necessary) falling the rest of the way. There must not be any dip which would harbour condense water. The utensil must have a cock to discharge the condense water as it collects. This cock is at the bottom of the utensil, while the steam supply is usually taken in at the top. These goods and the boilers do not as a rule figure in makers' lists, as they are almost invariably made to order to meet customers' requirements as to measurements, etc.

Boot Boiler for Steam Cooking.