Lubrication in a trunk engine

Text 03. Lubrication

An engine contains many moving parts, and to prevent any wear or damage as a result of friction, a lubricant must be applied between these parts. Lubricating oil has many properties that have positive influences on the engine. One of its properties is its cooling-ability – the lube oil will carry away the heat that is generated by the friction between the various moving parts.

Furthermore, lubricating oil has the ability to prevent impurities from clogging together. In stead, these particles will suspend and float on the surface of the liquid. This makes it easy to remove them. The lube oil will also serve as an anti-corrosive agent - it will prevent the forming of rust. The thin oil layer (or oil film) will seal off pits and scratches in cylinder walls. This will prevent a "blow by" - leaking of exhaust gases through the cylinder-liner. Finally, the thickness of the lubricant will reduce engine-noise considerably. This thickness of lubricating oil is indicated by the viscosity grade. When a liquid is very "viscous" it will resist the tendency to flow. A liquid of low viscosity, such as water, will flow very easily through pumps and piping systems.

When the engine-temperature rises, the viscosity of the oil will be reduced and the oil will become less effective. That is why it is very important to indicate the viscosity grade of a lubricant at higher temperatures.

The lube oil is stored in the drain tank. This oil sump, as it is also called, is often integrated in the double bottom. "Ullage" is the space between the surface of the oil and the top of the tank and will allow for the expansion of the oil when the engine gets hot. The air in this space will also expand, and to prevent the lubricant from being forced down by the pressure that will arise form the expansion of hot air, the drain tank is fitted with an air vent. This air vent, or breather, serves as an escape for the hot fumes that have accumulated in the drain tank. In a forced lubricating system the lube oil is pumped from the drain tank to the distribution branches in the engine and to the shafting. Before it is entered into the engine the used oil must first be filtered and cooled by seawater or fresh water.

Lubrication in a crosshead engine

In a crosshead engine oil bores lead the oil through the crankshaft, crankwebs and crankpins. From there the oil passes from the main bearing to the crank, connecting rod, crosshead, crosshead guide shoes and crosshead guides.

Lubrication in a trunk engine

The rotating crank causes an oil mist when it throws up the lube oil. The oil passes through the main lube-oil supply line to the crankshaft-bearings and camshaft- bearings, after which the used oil is passed through strainers before it returns to the drain tank. Before the lubricating oil is entered into the system again, it must be purified by another strainer in the drain tank. The oil-level in the drain tank can be measured with a sounding rod and read from a level gauge.

Date: 2016-03-03; view: 1040