Air is a freely available natural resource, yet we know how important it is for industrial processes. I will be talking here about the use of air on board various types of ships for different uses. A ship is a moving plant with different types of machineries which are required to take the plant from one place to other place. We learnt about air compressors in a previous article and know that compressed air is stored in tanks of appropriate capacity. This air can be used for various uses such as control purposes and this is known as control air. We will leave the discussion about process air or working air for later
Uses of compressed air for control
What we did not see in our article regarding air compressors was that the air is also filtered and dried out before being actually used for any purpose. After going through all the phases of compression, collection, pressure control, filtering and drying; finally the air is ready to be used for control purposes. There are many uses of control air on board ships.
Control air plays a vital role in propulsion of ship and it is used for controlling the function of ship engines including
- Ship’s engine speed
- Direction of running
The engine room of the ship is the power plant of the vessel and vital for its operation. There are many uses of control air in engine room which is widely known as the heart of the ship. Most of the pipe lines in engine rooms are fitted with valves. Some of these valves are manually operated but some valves related to critical operations also have pneumatic control which refers to the use of control air for opening and closing of these valves in a remote-controlled fashion.
Steam is a necessary ingredient on board ships and boiler in the engine room generates steam to heat the engine fuel, water and air. Control air is used to provide signals to these boilers during their operation.
As you will remember from the study about types of propellers on the ship; a propeller is basically a fan which rotates to move the ship. This propeller is driven by the main engine of the ship via a shaft which is protruding outside into the water from the ship’s hull. This shaft is known as the propeller shaft and it has a big diameter and you can well imagine what can happen with such a massive shaft protruding out from the ship. Obviously it needs an arrangement to seal the inflow of sea water from the place between the shaft and the space meant for the shaft to protrude out into the water.
You can see the propeller and rudder arrangement in the adjoining diagram
This penetration is sealed through combination of seals and control air thus preventing the open sea coming into engine room of the ship.
Hence we see that control air serves a lot of useful purposes on board a ship.