There are two types of drains:
• Controlled drains - the result of normal operation.• Uncontrolled drains - the result of abnormal operation.
When an engine stops, fuel from the fuel manifold and combustion chamber drains either overboard, or as is more usual into an 'ecology drain tank'. This tank is automatically emptied, (the fuel being fed back into the engine) next time the engine is run. (figure 19.16.)
Engine driven accessory drive shaft require lubrication. This will be provided by the engine lubrication system. To ensure proper lubrication, the drive shaft bearings are sealed to prevent loss of oil. These bearing seals are monitored for leaks, by the engine drain system which consists of a number of shrouds, enclosing the drive shaft bearing, and pipes leading either an overboard series of drain pipes or a collector tank. These drains are often referred to as ‘witness drains or dry drains' as if they exhibit signs of leakage they bear witness to a potential drive shaft failure.