Boiler Mountings: Comprehensive List With Functions

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.

Boiler Mountings: Comprehensive List With Functions

Also Read: Marine Boilers – Working, Types, Parts & Basics of Boilers

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:

  1. Steam Stop Valve
  2. Boiler Safety Valve
  3. Boiler Level Gauge Glass
  4. Air Vent
  5. Feed Check and Control Valve
  6. Pressure Gauge Connection
  7. Boiler Blowdown Valve
  8. Scum Blowdown Valve
  9. Sampling Connection
  10. Whistle Valve
  11. Low-Level Alarm
  12. Soot Blowers
  13. Automatic Feed Water Regulator
  14. Manhole
  15. Mud box
  16. TDS Sensor and Probe
  17. Fusible Plug

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Functions of Various Boiler Mountings

Let us now understand the purpose of these boiler mountings.

Steam Stop Valve

Steam Stop Valve
Courtesy: MechanicalJungle

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

Boiler Safety Valve
Courtesy: Nationwide Boiler Inc.

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

Boiler Level Gauge Glass
Courtesy: SaVRee

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

Boiler Air Vent
Courtesy: Bell and Gossett

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.

Also Read: Marine Oily Water Separator (OWS): Definition, Construction, Working, Regulations and More

Feed Check Control Valve

Feed Check Control Valve
Courtesy: Mechanical Engineering

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

Pressure Gauge Connection
Courtesy: Heating Help – The Wall

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

Boiler Blowdown Valve
Courtesy: Suraj Metal Corporation

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

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

Boiler Sampling Connection
Courtesy: The Process Piping

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

Whistle Valve in boiler

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

Boiler Low-level Alarm
Courtesy: Afriso

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

Boiler Soot Blowers
Courtesy: Trust Well Engineers India

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

Automatic Feed Water Regulator
Courtesy: Watts

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.


Boiler Manhole
Courtesy: Piping Fittings

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.


Boiler Mudbox
Courtesy: Machinery Spaces

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

Boiler TDS Sensor and Probe
Courtesy: Chemtrol

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

Boiler Fusible Plug
Courtesy: SaVRee

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.

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