Types of draught can also be divided into " induced draught ", where exhaust gases are pulled out of the boiler; " forced draught ", where fresh air is pushed into the boiler; and " balanced draught ", where both effects are employed.
42.
The " Royal Sovereign " s were powered by a pair of three-cylinder, vertical triple-expansion steam engines, each driving one shaft . Their engines were designed to produce a total of and a maximum speed of using steam provided by eight cylindrical boilers with forced draught.
43.
Very few steam locomotives have ever used a forced draught like this, the main reason is that in order to add fuel either the draft must be stopped or some form of airlock fitted . " Novelty " used an airlock to feed the fuel in, but there was still a chance of flame and hot gases being blown into the face of the fireman.
44.
At the previous six hour'full power trial of the " Pha�ton " there was a difficulty experienced in maintaining steam from want of draught in the stokeholds . ( Only the " Leander " of this class has been fitted with fans for forced draught . ) The funnels were afterwards raised from to ( the same height as those of the first-class cruisers ), while the space between the firebars was increased.
