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Lubricator is required on all moving parts of a steam locomotive.  Proper lubrication reduces frictional forces , prevents wear and improves sealing.  Cylinder lubrication can be provided by either a displacement or a mechanical lubricator.  Only steam cylinder oil should be used for cylinder lubrication.

Displacement Lubricator

The Roscoe displacement lubricator, show in Figure 39, functions because of the difference in specific gravity between water and oil.  In consist of an oil tank, which is connected by a small tube about 0.8 mm in diameter, to the tee steam pipe which feeds both cylinders as show in Figure 39.  When the steam enters the oil tank, it condenses into water.  Since the weight of the water is greater than that of an equal volume of oil, the water sinks to the bottom of the tank and forces the oil up into the steam line where it is picked up by the steam flow and distributed to the cylinders.  The process is repeated until the oil is exhausted. 


A small drain plug may be fitted to the tank and a needle shut off valve is sometime provided.  The amount of oil used varies with its quality as well as the ambient conditions and the work which the locomotive is doing.  Never operate your locomotive without first check the lubricator to insure it is properly filled. 


Figure 39 : Roscoe Displacement Lubricator


Mechanical Lubricator

There are two principal types of mechanical lubricators, the Wakefield type is the simplest.  The pump ram is activated by a scotch yoke or a cam / disc arrangement.  As the ram moves upwards and clears the induction port, a partial vacuum forms and oil flows in the ram cylinder.  When the ram reverses its direction and moves downward, covering the induction port, oil which remains in the cylinder if forced through the check valve and into the steam line leading to the cylinders.  The ram must fit snugly in its cylinder for the lubricator to operate.  If a vacuum does not form beneath the ram, oil will not flow into the ram cylinder and be pumped to the steam cylinders.  The ram is driven at a ratio of one stroke for every 20 to 30 revolutions of the drive wheels by means of a ratchet and pawl mechanism.  The drive motion is supplied by an eccentric on the axle or from the valve gear. 


Mr. L. Lawrence, know as L.B.S.C. to the model engineering fraternity, developed the oscillating mechanical lubricator.  It is more reliable than the Wakefield type but is also more complicated.  In consists of a small oscillating cylinder, installed inside the oil tank, which pumps oil to the steam cylinders.  It is driven by means of a ratchet and pawl arrangement.




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