Power Plant Engineering

244 POWER PLANT ENGINEERING

Liquid oils lubricants are most commonly used. Liquid lubricants are of two types:

(a) Mineral oils

(b) Fatty oils.

Graphite, white lead and mica are the solid lubricants.

Semi solid lubricants or greases as they are often called are made from mineral oils and fatty-oils.

8.10.1 LIQUID LUBRICANTS OR WET SUMP LUBRICATION SYSTEM
These systems employ a large capacity oil sump at the base of crank chamber, from which the oil
is drawn by a low-pressure oil pump and delivered to various parts. Oil then gradually returns back to
the sump after serving the purpose.
(a) Splash system. This system is used on some small four strokes, stationary engines. In this
case the caps on the big ends bearings of connecting rods are provided with scoops which, when the
connecting rod is in the lowest position, just dip into oil troughs and thus directs the oil through holes in
the caps to the big end bearings. Due to splash of oil it reaches the lower portion of the cylinder walls,
crankshaft and other parts requiring lubrication. Surplus oil eventually flows back to the oil sump. Oil
level in the troughs is maintained by means of an oil pump which takes oil from sump, through a filter.
Splash system is suitable for low and medium speed engines having moderate bearing load pres-
sures. For high performance engines, which normally operate at high bearing pressures and rubbing
speeds this system does not serve the purpose.
(b) Semi-pressure system. This method is a combination of splash and pressure systems. It
incorporates the advantages of both. In this case main supply of oil is located in the base of crank
chamber. Oil is drawn from the lower portion of the sump through a filter and is delivered by means of

Oil Troughs

Lower Oil Pan

Oil Pump

Main

Bearing

Connecting Rod

Bearing

Main

Bearing

Cam shaft

Oil Pressure Gauge

Oil strainer

Fig. 8.7. Semi Pressure System.