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Various types of pumps are used on board a ship, depending on requirement of pressure and flow. Apart from that, there are several other factors that are taken into consideration while selecting a pump for a specific purpose.
This article will describe three types of pumps having the same basic principle but differ in construction an working. Screw, Vane and Gear pumps are the three pumps that come under the category of positive displacement pumps. These pumps fall under the rotary pump type as pumping action is done as a result of rotating motion.
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General concept of Rotary Positive displacement pumps.
In all these types of pumps, except the screw pump, liquid is forced to travel circumferentially when displaced by the movement of vane or gear.
The only difference between screw pump and other rotary pumps is that the liquid displaced in screw pump moves axially, whereas in other rotary pumps it moves in a circumferential pattern. The main feature of these pumps is that they continue to force liquid into the system, in spite of any type of opposition in the transfer.
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Characteristics of Rotary Pumps
1. These pumps are adaptable to very high pressure operation.
2. Variable flow rate is possible through these pumps.
3. Maximum throughput is limited due to mechanical considerations.
4. The pumps are capable of efficient performance even at low volume throughput rates.
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Applications Of Rotary Pump
- The main applications where rotary pumps are used are - Refrigeration Heating and Air Conditioning.
- They are also used as pumps carrying out high viscosity substances transfer such as lubricating oil.Lobe-type, flexible-vane or screw pump are generally used for high viscosity or metering.
- Screw-type pumps are used for high density stocks such as Paper and pump.They are also used for Chemical Transfer and metering.
- Because of their positive displacement characteristics they are specifically used in Sewage Treatment plants for transfer of concentrated sludge and scum
- Maximum of the hydraulic pumps used for numerous applications on ship are of rotary type.
- Rotary pumps are also used as Water Supply and carbon slurry pump.
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Main Components Of Rotary Pump
The Main Components of any type of rotary pump are:
1. Pumping chamber - Pumping chamber of the rotary pump is the area which contains the pumped fluid when the pump is pumping. Fluid may enter the pump through one or more ports and can leaves through one or more outlet ports.
2. Casing - It is that part of the pump which surrounds the pumping chamber. It is also referred to as the housing,body or stator of the pump.
3. End plates - They serve to close off the ends of the body so as to form integral part of the pumping chamber. These plates can also be referred as the end covers.
4. Rotating assembly - It refers to all the moving parts inside the pump. The moving parts generally comprises of a driver and driving shaft. The driver shaft is turned by the motor and the driver is turned by the driving shaft.
5. Seal chamber - The cavity through which the driving shaft comes out or protrudes is called seal chamber and the leakage through this chamber is controlled either by a mechanical seal or by a normal packing material.
6. Seal -The seal can either be a mechanical seal or a normal packing material.The seals used should be leak proof when the pump is pumping any toxic substances. Cooling and lubrication of these seals is done by the same liquid which the pump is pumping
6. Relief valves - They are given so as to control the outlet pressure of the pump. As soon as the pressure increases above the pre-determined value, the relief valve lifts and releases the excess pressure to the inlet port, thus controlling the pressure. The relief valve is generally set 5-10% above the normal working condition.
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Marine Auxiliary Machinery, 7th Edition, 1995 by McGeorge
Pump Handbook- 4th Edition By Tata McGraw Hill
Types of Rotary Pumps on Ships
Learn about the various types of rotary pumps described in this article. Know the specifications of each of them and also find out the differences between them. Explore the various aspects of Rotary pump with this series.