General Overview of Types of Pumps on Ship
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.
A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action. A marine pump is an important auxiliary equipment in marine industry and ship building industry. It is widely used in all kinds of marine vessels, such as barges, tug boats, containers, carriers, ships, vessels, fixed offshore structure, drilling jack-up rigs and so on.
These marine pumps can be serviced for cooling, circulating, ballast, general service(G/S), fire-fighting, boiler feed water, condensate water, fresh(drinking) water, sanitary water, bilge & sludge, F.O. transfer, L.O. transfer, F.O. and F.S. cargo pumping, cargo stripping, hydrophonetank unit, sewage treatment unit, oil water separator, incinerator, fresh water generator, and so on.
Marine Pump Type
Marine pump is named by its usage or application, it covers a lot of types of pumps, such as :
Marine centrifugal pump is used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits.
Gear pump, a marine gear pump uses the meshing of gears to pump fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. Gear pumps are also widely used in chemical installations to pump high viscosity fluids. There are two main variations; external gear pumps which use two external spur gears, and internal gear pumps which use an external and an internal spur gears (internal spur gear teeth face inwards, see below). Gear pumps are positive displacement (or fixed displacement), meaning they pump a constant amount of fluid for each revolution. Some gear pumps are designed to function as either a motor or a pump.
Screw pump, a marine screw is a positive-displacement (PD) pump that use one or several screws to move fluids or solids along the screw(s) axis. In its simplest form (the Archimedes’ screw pump), a single screw rotates in a cylindrical cavity, thereby moving the material along the screw’s spindle.
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.
There are many types of Marine Pipes designed for specialized marine operations. These pipes are used in various mechanical operations on ships as well as in offshore systems. They are usually made from special metals that can withstand the harsh conditions of seawater. Without these specialized pipes, sailing through the marvelous seas wouldn’t be possible, not to mention other sea and offshore exploration processes such as oil drilling.
Unique Properties Of Marine Pipes
As noted earlier, the harsh conditions of seawater require that the pipes used for the different marine operations be made from a material that can withstand those conditions. Typically, one or more types of stainless steel is the material of choice for making a marine pipe, although other metals or materials are used too. Stainless steel is a steel-chromium alloy that is highly resistant to corrosion, and it’s commonly used in highly corrosive environments at the sea. It is also a very sturdy metal that allows for thinner pipes to be made for any type of application.
Also, the marine pipe is made from materials that are relatively lightweight, free of rust and other contamination, and easy to install. It should also be durable so that the pipes have a long service life.
Applications That Use Marine Pipes
As their name suggests, the marine pipe is built specially for use in marine operations and in marine vessel machinery. The type of metal used for marine applications is selected primarily for its corrosion resistance properties, above other characteristics. This is because corrosion resistance is extremely important in marine operations and aboard ships, more than anything else. Specifically, martensitic and ferritic stainless steel metals are normally used in corrosion-resistant marine pipes. However, Austenitic metals offer even increased corrosion-resistance and are used for the same purpose as the two aforementioned stainless steel types.
That said, there are a couple of other metals used for making these kinds of pipes, including galvanized steel, carbon steel, and glass fiber, among others.
Specific applications where the marine pipe is used include several ship operations such as onboard plumbing fixtures, saltwater piping, black and gray water piping, as well as vent and rain piping.