Lubricating oil System:
There are a number of components on the engine (like crank pin bearing, crankshaft bearings, camshaft bearings, various moving components etc) which are to be constantly lubricated. Most of the bearings are made of white metal and any failure of the lube oil system will damage the bearings. The lube oil system on the engine contains the following components.
- Two lube oil (L.O.) circulation pumps, one working + one standby.
- 1 duplex type Suction Filter (SF).
- Lube Oil Heat Exchanger.
- Lube Oil Thermostatic valve.
- 1 duplex type Discharge Filter (DF).
The Lubricating Oil after circulation through the bearings gets collected in the engine pump. From the engine pump the L.O. pumps (one working and the other standby) draw the oil through the suction filter (duplex type) and circulate through a heat exchanger for cooling.
For lube oil the viscosity at the inlet is important and hence at the inlet, a constant temperature is to be maintained. For varying loads on the engine, the temperature attained by L.O. will be varying and hence to maintain a constant temperature at the inlet, a bypass line is provided for the heat exchanger with a thermostatic valve. This thermostatic valve, depending on the temperature at the inlet of engine closes/opens the bypass line to maintain a constant temperature. (Normally the inlet temperature is 45-degree celsius for big engines).
The pumps provided are screw or gear type pumps with relief valves. The normal L.O. pressure will be about 3 to 5 bar.
Pressure switches are provided on the discharge side of the pumps to sense the pressure and to start the second pump in case of failure of the first pump. (by sending signal to starter of the second pump).
An alarm system is provided in control room to give an alarm in case of low lube oil pressure and to stop the engine in case of very low lube oil pressure.
On engines of high horsepower, separate Lube oil system is provided to take care of friction between cylinders and pistons. The cylinder lube oil system consists of a storage tank and small pumps (mounted on engines and driven hydraulically) and nozzles at various levels of a cylinder for injecting Lube oil between piston and cylinder.
The cylinder lube oil gets evaporated because of friction between cylinder and piston. The consumption of lube oil shall be about 0.8 to 1.0gm/BHP/Hr.
Cooling of Pistons by Lubricating Oil
On large bore engines, it is not sufficient to cool the cylinder jackets, since maximum temperature is generated at the centre of the cylinder bore by exhaust gases. Hence the pistons are cooled separately by circulating lubricating oil through the pistons.
In the next post, we shall talk about Fuel Oil System on board ships.