Sunday, January 15, 2012



12. The oil tank (fig. 8-4) is usually mounted on the engine and is normally a separate unit although it
may also be an integral part of the external gearbox. It must have provision to allow the lubrication system
to be drained and replenished. A sight glass or a system contents to be checked. The filler can be
Fig. 8-4 An oil tank.
either the gravity or pressure filling type; on some engines both types are fitted. Provision is also made
for a continuous supply of oil to be made available in aircraft which are designed to operate during
inverted flight conditions. Since air is mixed with the oil in the bearing chambers, a de-aerating device is
incorporated within the oil tank which removes the air from the returning oil.

13. The oil pumps are vital to the efficient operation of the engine. Failure of the pumps will necessitate a
rapid shutdown of the engine. For this reason, the oil pump driveshafts do not incorporate a weak shear-neck (Part 7) because they must continue to supply oil for as long as possible, regardless of damage.
14. As the feed oil is distributed to all the lubricated parts of the engine a substantial amount of sealing
air (Part 9) mixes with it and increases its volume. Additionally the bearing chambers operate under
differing pressures. Therefore, to prevent flooding it is usually necessary to have $. scavenge pump for
each chamber.

15. Gear type pumps are normally used in recircu-latory oil systems but vane and gerotor pumps are
employed in some engines. The simplicity of single-shot pumps (para. 19) make them ideal for engines
which run for a short duration and use the total loss type of oil system.

16. Gear pumps (fig. 8-5) consist of a pair of inter-meshing steel gears which are housed in a close
fitting aluminium casing. When the gears are rotated, oil is drawn into the pump, carried round between the
teeth and casing and delivered at the outlet.

17. Since a small quantity of incompressible oil becomes trapped in the gear mesh, which can cause
a hydraulic lock and possible pump damage, a relief slot is machined into the end faces of the casing to
provide an escape route for the oil.

18. Gear pumps are used both as pressure (feed) pumps and scavenge (return) pumps and are incor-porated within a common casing. The oil pumps pack is driven by the accessory drive system (Part 7).
19. Single-shot pumps (fig. 8-6) have a quantity of oil contained within a cylinder. When the piston is
forced up the cylinder bore, under the control of the throttle unit, the oil forces the outlet valves to open
allowing a flow of oil to the parts required to be lubricated. When the piston reaches the top of the
cylinder bore the outlet valves close due to the reduced oil pressure. Recharging of the oil pump dipstick must also be incorporated to allow the oil cylinder is achieved by a spring forcing the piston to
its original position. This reduces the pressure between the cylinder and the oil tank which allows
the oil replenshing valves to open until the cylinder is recharged.


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