Marine Boilers are one of the most important machinery onboard a ship. Early days, a ship’s propulsion would be powered by steam generated by the boiler but over time with technological revolutions, various devices called mountings have been introduced which work to maintain the safe operation of a boiler.
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What Are Boiler Mountings?
Before we head on straight into understanding the various types of mountings used on a boiler, let us first understand what exactly are boiler mountings.
Boiler Mountings are a set of devices that are installed for the safe operation of a boiler. Below mentioned is the complete list of boiler mountings:
Boiler Mountings are a set of devices that are installed for the safe operation of a boiler. Below mentioned is the complete list of boiler mountings:
- Steam Stop Valve
- Boiler Safety Valve
- Boiler Level Gauge Glass
- Air Vent
- Feed Check and Control Valve
- Pressure Gauge Connection
- Boiler Blowdown Valve
- Scum Blowdown Valve
- Sampling Connection
- Whistle Valve
- Low-Level Alarm
- Soot Blowers
- Automatic Feed Water Regulator
- Manhole
- Mud box
- TDS Sensor and Probe
- Fusible Plug
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Functions of Various Boiler Mountings
Let us now understand the purpose of these boiler mountings.
Steam Stop Valve
It is a valve that is connected to the boiler for proper regulation and distribution of steam from the boiler to the distribution lines. The main steam stop valve stays at the shut position normally to avoid the backflow of steam to the boiler. The valve body is usually made up of cast iron and the valve seat is made from gunmetal and the flange is bolted on the top of the steam drum.
Boiler Safety Valve
To avoid over-pressurizing, safety valves are an integral part of boiler construction. They are usually fitted on the boiler that has one superheater and the rest two on the steam drum. It is made of cast iron and two independent valves are fitted on the valve seat which is connected to a lever by the means of a pivot that is held tightly by a spring. This spring force keeps the valve shut under normal conditions and in cases of exceeding pressure when the pressure upwards exceeds the downwards, it opens and excess steam escapes into the atmosphere.
Boiler Level Gauge Glass
These are devices with the help of which we can check the water level present inside the boiler drum, the construction of the boiler glass gauge is decided based on the pressure of the boiler. It is a very important device since it tells us about the water level inside the steam drum,
Air Vent
This is fitted on a boiler to maintain the proper relationship between the air pressure inside the boiler and the atmospheric pressure outside to even out any pressure differences between the two and prevent implosion or explosion when the boiler is depressurized or pressurized.
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Feed Check Control Valve
This non-return type valve is responsible for the supply of steam as per the requirement and it is fitted in both main and auxiliary steam lines after the stop valve.
Pressure Gauge Connection
As the name suggests, this device is used to measure real-time pressure in given equipment. They can be fitted in a superheater, boiler drum, and on the steam or the water drum as necessary.
Boiler Blowdown Valve
Situated on the bottom side of the boiler, this can be used to empty the boiler for chloride water treatment or maintenance purposes at regular intervals.
Scum Blowdown Valve
Fitted on the normal water level, this shallow dish type of arrangement allows the segregation and blowdown of floating impurities, saturated salts, oil foaming from the water surface.
Sampling Connection
For proper operation of a boiler, feed water needs to be collected at regular intervals to test the properties of the water such as Total Dissolved Salts, or the pH or the type of water which is collected by opening this sample water cock anytime when desired.
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Whistle Valve
In ships where steam is used as a primary source of whistling, this non-return type valve provides the necessary steam pressure necessary to blow the whistle of the ship.
Low-level Alarm
One of the most important mountings is used to measure the amount of feedwater inside the boiler and gives out an alarm in case it is low. There is another mode called low-low level where the water content is extremely low and the fuel is cut off to preserve the boiler and prevent overheating.
Soot Blowers
These devices are used before the boiler is fired up to ensure that no soot or unburnt particles are left near the burner that may hamper its performance. It is usually operated by compressed air or steam and is used to clean the combustion chamber before use.
Automatic Feed Water Regulator
Fitted on the feed line, this mounting ensures that there is an appropriate water level in the boiler at all times which is essential. In cases of boilers that have high evaporation ate, a multiple element feedwater control system is used.
Manhole
These are holes that lead into the boiler which are essential for inspection and introspection of the boiler. The crew goes in through these holes at regular intervals and ensures that the materials are all fit for use and there are no cracks or cavitation in the boiler. Usually, one opening is at the steam drum and another one is at the water drum.
Mudbox
As the name suggests, it is used to collect impurities, particulates, and mud that get accumulated in the bottom of the boiler. It is present in the bottom side of the boiler from where all these impurities can be collected with ease.
TDS Sensor and Probe
TDS or Total Dissolved Salts refers to the number of salt particles present in a given quantity of water and is measured in ppm (parts per million). Too much TDS will lead to the deposition of scales on the walls of the boiler which will lead to uneven heating and lower the efficiency of the boiler and thus the extra fuel will be consumed to heat the same quantity of water. If the sensor detects that there are too many salts present in a given quantity of water then a manual blowdown should be initiated and new feedwater with lower TDS content should be introduced after hearing the audiovisual alarm.
Fusible Plug
A fusible plug is a threaded device made up of gunmetal and has tappet holes drilled in it which are usually filled with an alloy of tin having a low melting point. These are usually fire actuated or steam actuated and are typically fitted over the combustion chamber.
During normal working conditions, one of the sides of the plug is always exposed to extreme pressure and temperature while the other is submerged underwater. In case the water level reaches below a safe level, the plug tip is exposed to the steam thus melting it and exposing the combustion chamber with steam. This sudden exposure of steam will cut out the fire and stop fire thus protecting the boiler from any kind of damage.