an injector at the top of the article. Exhaust steam from the cylinders is directed through a nozzle on the end of the blastpipe, to reduce pressure inside the smokebox by entraining the flue gases from the boiler which are then ejected via the chimney. The effect is to increase the draught on the fire to a degree proportional to the rate of steam consumption, so that as more steam is used, more heat is generated from the fire and steam production is also increased. The effect was first noted by Richard Trevithick and subsequently developed empirically by the early locomotive engineers; Stephenson's Rocket made use of it, and this constitutes much of the reason for its notably improved performance in comparison with contemporary machines. Modern uses The use of injectors (or ejectors) in various industrial applications has become quite common due to their relative simplicity and adaptability. For example: To inject chemicals into the boiler drums of small, stationary, low pressure boilers. In large, high-pressure modern boilers, usage of injectors for chemical dosing is not possible due to their limited outlet pressures. In thermal power stations, they are used for the removal of the boiler bottom ash, the removal of fly ash from the hoppers of the electrostatic precipitators used to remove that ash from the boiler flue gas, and for drawing a vacuum pressure in steam turbine exhaust condensers. Jet pumps have been used in boiling water nuclear reactors to circulate the coolant fluid. For use in producing a vacuum pressure in steam jet cooling systems. For expansion work recovery in air conditioning and refrigeration systems. For enhanced oil recovery processes in the oil & gas Industry. For the bulk handling of grains or other granular or powdered materials. The construction industry uses them for pumping turbid water and slurries. Eductors are used in ships to pump residual ballast water, or cargo oil which cannot be removed using centrifugal pumps due to loss of suction head and may damage the centrifugal pump if run dry, which may be caused due to trim or list of the ship. Eductors are used on-board ships to pump out bilges, since using centrifugal pump would not be feasible as the suction head may be lost frequently. Some aircraft (mostly earlier designs) use an ejector attached to the fuselage to provide vacuum for gyroscopic instruments such as an attitude indicator (artificial horizon). Eductors