Reverse Osmosis Generators For Ships - The Working Principle

Written by johnhansen Friday, 08 January 2010 18:42

Ships are always surrounded by literally unlimited quantity of water, except perhaps when undergoing drydock repairs. Since there are human beings on board on all types of ships, we certainly need drinking water on board. We have already studied about the machine known as the fresh water generator which is used to produce pure water out of the salty sea water.

Thermostatic Expansion Valve or TEV

Written by johnhansen Friday, 08 January 2010 18:34

Thermostatic expansion valve is one of the most commonly used throttling devices in the refrigeration and air conditioning systems. Let us see the details of this valve that automatically maintains the flow of the refrigerant inside the evaporator.

What is Thermostatic Expansion Valve or TEV?

Thermostatic expansion valve or TEV is one of the most commonly used throttling devices in the refrigerator and air conditioning systems. The thermostatic expansion valve is the automatic valve that maintains proper flow of the refrigerant in the evaporator as per the load inside the evaporator. If the load inside the evaporator is higher it allows the increase in flow of the refrigerant and when the load reduces it allows the reduction in the flow of the refrigerant. This leads to highly efficient working of the compressor and the whole refrigeration and the air conditioning plant.

Properties of Distillate and Residual Fuels

Written by Bobby Monday, 27 July 2009 02:41

Density
This is the mass per unit volume and is generally given as kg/m³ at 15^OC and is specifcially given as that found in a vacuum. The density reduces with increasing temperature and alos reduces in air although the latter by only about 0.1%.

What is a Lubricating Grease?

Written by Bobby Monday, 27 July 2009 02:02

A lubricating grease is a solid or semi-fluid lubricant containing a thickening agent in a liquid lubricant. Grease can be likened to a sponge soaked in lubricant. In cases of a soap based grease the soap can be likened to the sponge soaked in a mineral oil as the lubricant.
They are usually made from mineral oil stock of widely ranging viscosity but similar to those used for liquid lubricants. Synthetic oils may also be used were high temperatures are expected.

Explosimeter and Oxygen Analysers

Written by Bobby Thursday, 23 July 2009 08:07

A sample of gas is drawn into the sample chamber using the hand pump. Any combustibles land on the surface of the hot wire and burn increaseing the temperature of the wire thereby increaseing the resistance.

Fixed Fire Fighting Installations for enclosed Spaces Rules and Regulations

Written by Bobby Thursday, 23 July 2009 07:45

Gas fire-extinguishing systems in machinery spaces
The use of a fire-extinguishing medium which, either by itself or under expected conditions of use, gives off toxic gases in such quantities as to endanger persons is not permitted. New installations that use fire-extinguishing media, which have ozone-depleting properties under the Montreal Protocol, are not permitted.

Sprinkler of the Fire fighting Systems

Written by Bobby Thursday, 23 July 2009 07:32

Must be fitted to passenger ships carrying less than 36 passengers in the accommodation spaces and other areas considered necessary be the administration. For pasenger ships carrying greater than 36 passengers it must be fitted to accommodation spaces, corridors, stairwells and to control stations ( the latter may be served by an alternative system to prevent damage). The system must be of an approved type. See below for full requirements.
Generally takes the form of a wet pipe (line continuosly flooded) on to which are connected a number of sprinkler head. These heads consist of a valve held shut by a high expansion fluid filled quartzoid bulb. A small air space is incorporated.

When a fire occurs in an adjacent area to this bulb the fluid expands until the air space is filled, increasing internal pressure causes the bulb to fracture. The size of the air gap determines the temperature at which this failure occurs. The valve plug falls out and a jet of water exits , striking the spray generator where it is then distributed evenly over the surrounding area. In acting this way only the area of the fire is deluged and damage is minimised.

Water is supplied from an air pressurised water tank ( thus the system functions without electrical power), this water is fresh water to minimise damage. The tank is half filled with water and the rest is compressed air at pressure sufficient to ensure that all the water is delivered to the highest sprinkler at sprinkler head working pressure. Once this source of water is exhausted, falling main pressure is detected by a pressure switch. This activates a sea water supply pump. A valve is fitted on the system to allow proper testing of this function. After sea water has entered the system proper flushing with fresh water is required to prevent corrosion

A shore connection may be connected to the system to allow function during dry-dock

High Pressure Water spray system
A similar but essentially different system exists for the supply of water under pressure to dry pipes onto which sprinkler heads are fitted. These sprinkler heads do not have the bulb and valve arrangement. Instead when an area is to be served a relevant isolation valves is opened. The fundamental difference between this and the sprinkler system is that human intervention is required, whereas the sprinkler system is required to be fully automated. Commonly a cross connection vai a non-return valve exists able to deliver to the water from the high pressure spray system to the sprinkler system.

When an isolation valve is opened pressure in the line falls and the sea water pump is started. The air vessel is there to prevent cycling of the pump due to slight water leakage. The fresh water pump is there for flushing and initial filling of wet pipe only.

Water Fixed Fire fighting systems

Written by Bobby Thursday, 23 July 2009 06:51

Capacity of fire pumps
The capacity of the fire pumps is calculated as a product of the breadth, depth and length of the vessel but need not exceed 25m³ per hour.
Fire pumps
For cargo ships of 150 gross tons or more, a minimum of one fixed power pump and one portable pump are to be provided.
For cargo ships of less than 150 gross tons, one portable pump or alternative , is to be provided. which meets the criteria listed later
For fishing vessels, not less than one fixed power pump is to be provided.

Inert Gas Plant System

Written by Bobby Thursday, 23 July 2009 06:48

Components of plant
Boiler uptake valve- Provides a take off point for the flue gas, A cleaning arrangement is fitted to prevent soot build up.

Scrubber- Flue gas passes to the scrubber via the uptake valve, here it enters at the bottom via a waterseal and passes up through a series of sea water sprays and baffle plates being cooled and cleaned before exiting via a demister.

The operation of Inert Gas System

Written by Bobby Sunday, 19 July 2009 01:39

Definitions:
Inert gas- This is a gas which contains insufficient oxygen to support combustion of hydrocarbons

Inert conditions- This is where a space has had its oxygen content reduced to 8% or less

Inert gas plant- This is a system specially designed to supply cool, clean, pressurised, monitored and controlled inert gas.