A pump is a device used to move fluids, such as liquids, gases or slurries.
A pump displaces a volume by physical or mechanical action. Pumps fall into five major groups: direct lift, displacement, velocity, buoyancy and gravity pumps.Their names describe the method for moving a fluid. Pumps which are commonly seen in the engine room are Centrifugal pumps, Gear Pumps, Reciprocating Pumps, Eductors.
A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure and flow rate of a fluid. Centrifugal pumps are the most common type of pump used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward or axially into a diffuser or volute chamber, from where it exits into the downstream piping system. Centrifugal pumps are typically used for large discharge through smaller heads. These type of pumps are used are used in the marine industry for Ballasting, Fire pumps, General Service Pumps, Sea water Service pumps, Sea Water cooling pumps, Distallate pumps, Fresh Water Jacket Cooling Pumps and etc usually it is use with tranferring water only and not oil.
This uses two meshed gears rotating in a closely fitted casing. Fluid is pumped around the outer periphery by being trapped in the tooth spaces. It does not travel back on the meshed part, since the teeth mesh closely in the centre. it is also used in various hydraulic power packs.Since this is a very strong pumps which can withstand high pressures and can carry heavy liquids it is mainly used to transfer oils onboard ships. Such as Fuel Oil Transfer Pumps, Fuel Oil Supply Pumps, Pumps for feeding the FO Purifier, Pumps for circulating lube oil and etc.
Reciprocating pumps are those which cause the fluid to move using one or more oscillating pistons, plungers or membranes (diaphragms).
This uses a jet, often of steam, to create a low pressure. This low pressure sucks in fluid and propels it into a higher pressure region. Mainly used for stripping water in Ballast tanks. This is because if you use other pumps to strip the ballast tanks, the pumps might be air-bound when ballast tank is already empty thus the packing gets burned due to no water cooling. Making Eductors the practical way to Strip Water from Tanks.