145) The function of a D-slide valve is to exhaust steam from the cylinder at proper moment.

146) The mechanical draught produces more draught than natural draught.

147) The water tube boilers produce steam at a __________ pressure than that of fire tube boilers.

148) The mechanical draught __________ with the amount of smoke.

149) When the expansion of steam is carried out in a single cylinder and then exhausted into the atmosphere or a condenser, the engine is said to be a simple steam engine.