A ship consists of various types of machinery and systems. In many of these systems water and other fluids are used for cooling as well as other operations such as heating, crew facilities, lubrication, and others. Various marine pumps must be used for all these kinds of fluids to circulate inside the different systems.
Pumps can be independently driven by the ship power supply or attached to the machinery itself. All the systems on board a vessel require a proper operational pumping system so that the ship can sail smoothly through the seas.
Principles of Operation
In general, pumps are machines that use energy to move fluids from one compartment to another through a system of tubes. For this system to work pumps have to create suction from one compartment and discharge to another while providing energy to the fluid. Likewise, energy is needed to pump fluids from a lower-pressure compartment to a higher one. Thus that is also a job for a marine pump.
The use of pumps is necessary when we have:
- Liquid flow from lower to equal or higher energy level
- An increase in fluid supply
The type of pump we select for a system depends on the characteristics of the fluid to be circulated. Characteristics such as viscosity, density, surface tension, and compressibility are all considered. Also characteristics of the system such as require rate of fluid, temperature and pressure are also taken into account.
Types of Marine Pumps
There are many types of pumps inside a ship's machinery its one with special charateristics depending on the circulated fluid and other parameters. The study of the internal facilities and the special characteristics of each ship, are necessary for the proper selection of the pumps to be used.
Characteristics such as viscosity, density, surface tension and compressibility, along with characteristics of the system such as temperature encountered, and pressure tackled by the fluid, are taken into account.
However, the important criterion that allows the systematic classification and study of pumps is the way they transfer mechanical energy to the fluid.
In that regard we have the following basic types.
Positive Displacement or Static Type Pumps
Positive displacement pumps are priming devices that deliver an almost constant flow rate regardless of the pressure against which they are pumping. This is because the pump traps a fixed amount of fluid in each cycle and displaces it, making the flow rate predictable and consistent.
This kind of pumps are normally used where the discharge rate is small to medium and the viscosity of the fluid is high. These pumps can generate high pressures due to their design. Since they trap and move a fixed volume of fluid, they can build up pressure in the system if the discharge is restricted, unlike for example centrifugal pumps, which would merely reduce the flow rate under similar conditions.
Many positive displacement pumps are self-priming, meaning they can evacuate air from the suction line and begin pumping the fluid without needing the pump casing to be filled with the fluid first.
Subcategories
There are different subcategories of Static type pumps such as: Piston pumps, Diaphgram, Single Rotor, Multiple Rotor pumps.
Photo courtesy of marineinsight.com
Rotodynamic or Kinetic-type Pumps
Rotary dynamic marine pumps are one of the main categories of pumps, according to the basic division we made above. Their function is based on changing the kinetic state of the liquid by converting the energy imparted to it.
Initially, the mechanical work is converted into the kinetic energy of the fluid and then part of this kinetic energy is converted into pressure energy in the extraction (pump depression). Thus, the high flow velocity that is initially imparted to the liquid by the rotor, is converted into pressure. As stated by the Bernoulli Theorem.
Rotodynamic marine pumps are normally used for moderate to high discharge fluid rate. The pressure differential range for this type of pumps is in a range of low to moderate. Another popular use is in a system with low viscosity fluids.
Subcategories
Rotodynamic, Centrifugal, Mixed flow or Axial Flow pumps are some common subcategories of kinetic-type pumps.
Maintenance and Care
The following points must be emphasized regarding the maintenance and safety considerations of ship pumps.
Regular Inspection: Pumps must be regularly inspected for signs of wear, corrosion, or damage to impellers, seals, and bearings.
Proper Lubrication: Service departments must ensure that all moving parts are adequately lubricated to prevent friction and wear.
Seal Integrity: Maintaining the integrity of seals to prevent leaks and maintain efficiency.
Monitoring for Cavitation: Preventing cavitation through proper NPSH management and monitoring pump operation.
Understanding these basic maintenance principles, screws can ensure efficient and reliable fluid handling for all critical operations on board.
At Oceantech Shipping & Trading Ltd., we are deeply committed to ensuring reliable ship operations through proper maintenance and that of course includes pumps.
Should you need more information about pumps parts and maintenance, you can contact us:
Email: oceantech@ost.gr
Tel: +30 2130337678