A ship consists of various types of fluids moving inside different machinery and systems for the purpose of cooling, heating, lubrication, and as fuels. These liquids are circulated by different types of pumps, which can be independently driven by ship power supply or attached to the machinery itself. All the systems on board ship require proper operational and compatible pump and pumping system so that ship can run on its voyage smoothly.
The selection of a type of pump for a system depends on the characteristics of the fluid to be pumped or circulated. Characteristics such as viscosity, density, surface tension and compressibility, along with characteristics of the system such as require rate of fluid, head to which the fluid is to be pumped, temperature encountered in the system, and pressure tackled by the fluid in the system, are taken into account.
Types of Pumps
The pumps used on board are broadly classified into two types:
Positive Displacement Pump
Positive displacement pumps are self priming pumps and are normally used as priming devices.
- They consist of one or more chamber, depending upon the construction, and the chambers are alternatively filled and emptied.
- The positive displacement pumps are normally used where the discharge rate is small to medium.
- They are popularly used where the viscosity of the fluid is high.
- They are generally used to produce high pressure in the pumping system.
Dynamic Pressure or Roto-Dynamic Pump.
- In dynamic pressure pump, during pumping action, tangential force is imparted which accelerates the fluid normally by rotation of impeller.
- Some systems which contain dynamic pump may require positive displacement pump for priming.
- They are normally used for moderate to high discharge rate.
- The pressure differential range for this type of pumps is in a range of low to moderate.
- They are popularly used in a system where low viscosity fluids are used.
These broad classification of pumps are further differentiates by their constructional properties and popularity of usage onboard ship;
Positive Displacement pump:
- Reciprocating Pump
- Screw pump
- Gear pump
- Piston pump
- Ram type pump
- Vane pump
Dynamic pressure pumps:
- Centrifugal pumps
- Axial flow pumps
- Submersible pump
- Centrifugal-axial (mixed) pump.