Marine pumps refer to all kinds of pumps used by ships that meet the requirements of ship specifications and marine technical conditions. On ships they are often used to transport various liquids such as sea water, fresh water, sewage, oil and fuel.
 
Marine pump refers to the ship to increase the pressure of liquid and liquid material or position can make the flow of machinery. Transporting liquid to a higher location, a longer distance, and a higher pressure generally must use a pump. The pump can also be used to generate high-pressure liquid for hydraulic transmission. The pump is driven by an electric motor or other prime mover. The characteristics of the marine pump are: when the pump is required to swing and tilt in the ship, it is not possible to cause cavitation due to the fluctuation of the suction liquid level; in order to reduce the occupied area of the pump and facilitate maintenance, the vertical structure is generally adopted; the flow-through parts are made of bronze, brass or stainless steel to reduce corrosion as much as possible.
 
Marine pumps are widely used in modern ships. Generally speaking, a diesel-powered cargo ship needs 36 to 50 pumps of various types, accounting for 20% to 30% of the total ship machinery and equipment.
 
1. marine pumps are widely used in modern ships. According to their different uses, they can be divided:
 
(1) Pumps for ship power plants. There are fuel pump, lubricating oil pump, sea water pump, fresh water pump, hydraulic pump of steering gear or other deck machinery, feed pump of boiler device, cooling water pump of refrigeration device, sea water pump and condensate pump of seawater desalination device, etc.
 
(2) General purpose pumps for ships. There are bilge pumps, ballast pumps, fire pumps, daily fresh water pumps, daily sea water pumps, hot water circulating pumps, and general pumps for ballast, fire fighting and bilge pumps.
 
(3) Special pumps for special ships. Some special purpose ships are also equipped with special pumps for their special operating requirements, such as cargo oil pumps for oil tankers, mud pumps for dredgers, salvage pumps on salvage ships, water jet propulsion pumps on water jet propulsion ships, fishing pumps on non-net fishing vessels, etc.
 
2., according to the working principle of the pump, marine pumps mainly have the following categories:
 
(1) positive displacement pump
The positive displacement pump sucks and discharges liquid by periodically increasing or decreasing the working volume due to the movement of the working parts. When the working volume increases and the pressure decreases, the liquid is sucked in, and when the working volume decreases and the pressure increases, the liquid is discharged. Squeeze and directly increase the pressure of the liquid. According to the moving parts of the movement of different ways, it can be divided into two types of reciprocating pump and rotary pump. The former has a piston pump and plunger pump; the latter has a gear pump, screw pump, vane pump and so on.
 
(2) Impeller pump
The impeller pump relies on the impeller to drive the liquid to make high-speed rotary motion, continuously produce suction and discharge, and transfer mechanical energy to the conveyed liquid, so that the pressure of the liquid can be increased and the purpose of conveying the liquid can be achieved. According to the different characteristics of the impeller and flow structure of the pump, it can be divided into centrifugal pump and vortex pump.
 
(3) Jet pump
Jet pump is to rely on a certain pressure of the working fluid in the nozzle to produce a high-speed jet to lead the jet body, and then through the momentum exchange to be led to the increase in the energy of the jet body. Depending on the working fluid used, it can be divided into water jet pump, steam jet pump and air jet pump.
 
In addition to the pump according to the different working principle of classification, but also according to the pump shaft position is divided into vertical pump and horizontal pump; according to the number of suction port is divided into single suction pump and double suction pump; according to the prime mover driving the pump is divided into electric pump, steam pump and diesel engine pump. Generally, the ship is named for the pump according to the function of the pump, such as the main engine seawater cooling pump, the main engine oil pump, etc.