Introduction: Auxiliary equipment And maintenance work
Valves onboard
Valves are the most important of any system that has to deal with the flow of fluids [liquids or gases]. Basic requirement in a system is to control the flow to achieve required functions.
Valves are designed and incorporated in a system to achieve required functions.
- To stop and allow the flow
- To control the amount of flow
- To control the direction of flow
- Relieve of pressure hence preventing any breakdown of system
- With other devices maintain pressure/level/temperature
- To execute uni-directional flow
Types of Valve
1. Globe Valve:
A valve is lifted or lowered against a valve seat to allow or restrict the flow of fluid from one side to the other.
Valve body is of a shape of a globe with provision of flanges for attachment to the pipes in the system.
Valve disc is moved up by means of a spindle which can be operated by turning the hand wheel or a remote-control device.
Valves and seats can wear due to erosion or due to mechanical damage
in operation. However, discs and seats can be reground or re-machined or replaced easily in the same body of valve.
2. Gate or sluice valve:
The disc is raised and lowered like in case of globe valve by the handwheel at the threaded part of the spindle.
It has advantage over the globe valve for straight flow characteristics. Fluid can flow with little obstruction, no change in direction and hence little loss i.e. pressure drop.
It is not used for varying the flow of fluid, used just to stop and allow the flow in a particular system.
3. Cock or plug
Check valves commonly allows flow in one direction and automatically closes when the flow is reversed hence, they are also known as ‘non-return valves.
Non-return valves are fitted on the bilge line and ship side discharge valves to prevent water flowing back to bilges.
It is also used in the steam and boiler feed water system to prevent backflow of water.
4. Butterfly valve
Butterfly valves are a family of quarter-turn valves and work very similar to ball valves. The ‘butterfly’ is a disk connected to a rod.
When the valve opens, the disk rotates to allow fluid to pass through. It closes when the rod rotates the disc by a quarter turn to a position perpendicular to the flow direction.
Butterfly valves are popular for on-off or modulating services due to their lightweight, small installation footprint, lower costs, quick operation, and availability in huge sizes. These valves can be operated by handles, gears, or automatic actuators.
5. Check valves
Plug valves are valves that have cylindrical or conically tapered “plugs” inside the valve body that can be moved to control flow through the valve.
When the valve is open, the plugs in plug valves contain one or more hollow tunnels running sideways through the plug, allowing fluid to flow through the plug.
When the plug is turned 90° from the open position, the solid part of the plug blocks the ports and stops fluid flow.
Types of pumps onboard
1. Reciprocating:
Reciprocating pump is the term that is used for the pumps that perform to and from motion to displace fluid from suction line to discharge line. It moves water or other liquids by a plunger or piston that travels back and forth inside a cylinder.
This type of pump is in common use as a bilge pump or tank stripping pump. The design is simple, robust, and reliable.
Materials are very much dependent on the usage but bronze is common for larger parts and stainless steel for piston rods.
2. Centrifugal pump:
These pumps are among the top used pumps in various industries for transferring fluids.
They are undisputed champions for transferring low viscous fluids from one place to another across industries.
They are mostly used for their advantage of caring large quantity fluid, high flow rate with dynamic head. Above all the freedom to change flow-rate without dangerously pressurizing the system make it the top choice.
They are used on shore for boiler feed applications, irrigation, waste management, as a booster pump, refineries, mining, air conditioning, firefighting, food production and power generation.
These pumps are used on ship’s for bilges, boiler feed, firefighting, sea water suction and general service pump.
3. Gear pump
A gear pump basically have gears and these gears are responsible for providing pressure energy to the fluid flowing through it.
They mainly find their application in FO and LO purposes, transfer pumps, aux. engines , purifiers , stern tube lubrication etc.
4. Screw pumps
A screw pump is a subset of positive displacement pump that use one or more than one screw; to perform pump action along its spindle axis.
The complete assembly consists of two main parts; the driving motor ( prime mover ) and the pump assembly.
The motor provides the necessary rotary motion to the pump drive screw coupled to its shaft; which combined with low clearance in between screw create suction pressure With better suction capabilities and low maintenance for the same range of speed; it is also regarded as the most reliable pump for a variety of operation.
A screw pump is known for its low turbulence, ease of use with high viscous fluids, low vibration; self-primed and ability to work with minimal air pocket in fluid with low operating noise.
Screw pumps are best suited for application such as; fuel transfer, high pressure fuel injection, lubrication and hydraulic power implication
5. Eductors
These are basically used for de-ballasting purpose; it sucks out the ballast water from the tanks with the aid of vacuum created inside it by Bernoulli’s principal.
Parts of air compressor
Gaskets and packing on ships
Joints of soft material are used between two parts to ensure proper sealing. Joints need to withstand the operating temperature, pressures and fluid within the equipment.
Ring type joints are commonly used for valves, pipes etc.
Soft packing is used to prevent leakages between the casing and rotating shafts of a pump, valves and machines.
Packing is placed in the stuffing box and retained in place by a gland.
The packing gets worn and gland needs to be tightened a bit to achieve the seal.
Modern pumps and rotating machinery have a ready-made mechanical seal made of carbon rings, springs, o ring etc.
Strainers and filters
Strainers and filters are used to remove solid particle. They come in different designs, size and fineness of the filtering element.
Strainers separate large particles and filters are used to separate fine micro particles.
Strainers are usually fitted at the suction of the pump and filters are usually fitted at the discharge side of the pump.
Centrifugal purifier on ships
A high-speed centrifuge is a type of separator which is used on a ship to remove contamination from liquids such as fuel and lube oils.
The task of the centrifuge is to remove solid contamination from liquid and to remove undesirable liquid (water) from useful liquids (fuel).
The separation principle of high-speed centrifuge depends on the difference in the specific gravity of two different liquids.
Fresh water generator
A ship or cruise ship can only take so much water from shore facilities. It is not only uneconomical, but it also varies in quality from port to port.
Using fresh water generator or reverse osmosis plant. Basically, it takes in the water from sea to produce drinkable fresh water; using a process known as desalination.
Advantages of using fresh water onboard
- Increased cargo carrying capacity
- Cost saving by avoiding water purchases
- Availability of high quality water for boiler
- Eliminates risk of water shortages
- High quality water for drinking and domestic uses
- Saves maintenance and operational cost for sanitary and water supply systems
Domestic fresh water supply system
A hydrophore system is used on a ship to maintain constant water pressure to all parts of a ship (varying over different lengths and heights) at all times without continuous pump operation.
Hydrophore system is used onboard to provide water to all compartments and decks on a ship.
There is the continuous use of water on the ship from drinking to sanitary purposes.
We have domestic and drinking freshwater system onboard ship which utilize the pressure in hydrophore tanks to supply fresh water.
Freshwater from the domestic fresh water tank is pumped to
the hydrophore tank through any of the two pumps.
These pumps are controlled by the pressure switches installed on hydrophore tanks.
When the pressure inside the hydrophore reduced to a certain value the pump start.
On board ship, there is a separate hydrophore tank and supply line for drinking water known as drinking fresh water line.
Strainers and filters
Air conditioners have three main components: a compressor, a condenser coil, and an evaporator coil.
They also have a special chemical called refrigerant that loops through the system absorbing and removing heat.
Working together these three components convert the refrigerant from gas to liquid and back to gas quickly.
Refrigerants have a pretty cool superpower – the power to go back and forth from a liquid to a gas very easily which makes them very useful in the air conditioning system.
Boiler/steam system on ships-
- Steam Stop valve : The function of this valve is to stop or allow the flow of steam from the boiler to the steam distribution pipeline.
- Safety valves: Its function is to release steam to the atmosphere when the pressure within boiler reaches the maximum design pressure.
- Water level indicators: Used for indicating the level of water in the boiler.
- Feed check valves: These non-return type globe valves which allows feed water under pressure to pass into the boiler and to prevent any water escaping back.
- Pressure gauge: Its function is to indicate steam pressure of the boiler.
- Blow off cock: Its function is to
- remove sediments collected at bottom of boiler
- empty the boiler when it has to be cleaned,
- lower water level, if it becomes high.
- Manhole door:It is to provide an opening through which a man can enter a boiler for cleaning and inspection.
Types of waste materials & their disposal method on ships
Dirt and carbon parts from cleaned parts: Collect it and land it ashore
Waste oil and gases:Collect and incinerate or land it ashore
Broken, rejected parts and metal shavings:Collect and land ashore
Rubber rings, joints, insulated material, plastic materials:Collect and land ashore
Oily rags and oil-soaked waste: Incinerate or land it ashore
Chemicals used for cleaning:Store and land them ashore
Wood, saw dust, paper packing materials:incinerate
Oily water separator
Engine room bilges cannot be pumped overboard directly according to MARPOL; thus, it has to filtered through oily water separator.
OWS removes all the traces of oil from bilge water.
Oily water enters the first stage with the use of reciprocating bilge pump where there are conical disc welded to central perforated pipe.
Oil droplets adhere from the surface and gets separated from the water.
Oil is lighter than water is collected at top of the dome.
In the second stage the fine filters are provided which separates the fine oil droplets from water and separated oil is collected at the top of second stage chamber.
Then dirty water is passed through 15 ppm oil content in the sample. If not under the limit than it is held back to bilge holding tank via 3-way valve.
Sewage treatment plant
A sewage treatment plant is designed to treat and process raw sewage over different steps involving breaking, filtering, settling, controlled aerobic decomposition and chemical treatment.
The sewage produced is first treated and then discharged.
The process used to systematically break the sewage into small parts; using biological and chemical method is known as sewage treatment.
A sewage treatment plant on ship consists of a screen filter, primary chamber, aeration chamber, demisters, blowers, settlement and chlorination chamber.
Together they treat and discharge waste to comply with Marpol regulation IV. Oxygen in the air is used by bacteria to digest the sewage.
Propellor and shafting system on ships
