A Comprehensive Guide to Boiler Mountings

A Comprehensive Guide to Boiler Mountings

Boiler mountings are a group of safety devices installed to ensure the safe operation of a boiler. A boiler shell has seven main mountings: a safety valve, a steam stop valve, a vent valve, a pressure gauge, a water level indicator, a feed check valve, and a fusible plug.

This equipment protects the boiler from damage caused by extreme pressure, steam backflow, shell collapse due to vacuum, unregulated steam pressure, low water level, backflow of feed water to the pump, and dry running. 

Accidents and boiler breakdowns can occur as a result of poor maintenance and cleaning. Without boiler mounting, a single mistake can damage the boiler and its surroundings, resulting in a chain of events.

Without a high lift safety valve, the shell could explode, resulting in significant loss of life and machinery; similarly, a shell could collapse under vacuum if an air vent is not present during cooling down.

Since there is an increased demand for steam during cargo operations, the mountings make it easier and safer to operate the boiler.

 Boiler Parts – Mountings 

  • Pressure Gauge Connection
  • Main Steam Stop Valve
  • Auxiliary Steam Stop Valve
  • Water level gauge Glass
  • Scum Blow Down Valve
  • Low Level Alarm
  • Sampling Connection
  • Safety Valve
  • Feed check Valve
  • Air Vent Valve
  • Blow Down Valve
  • Whistle Valve

  • Automatic Feed valve Regulator
  • TDS Sensor and Sample
  • Manhole
  • Mud box
  • Soot Blower

Safety Valves

Boiler Parts include safety valves, which are installed on all boilers to prevent over-pressurization. Normally, three safety valves are installed on the boiler, one on the superheater and the other two on the steam drum. These valves must not be less than two in number and must lift at a pressure 3% above the boiler working pressure, regardless of boiler type.

A steam valve is composed of a cast iron body with two independent valves installed on the valve seat. These valves are linked to a lever by a pivot held in place by a spring.

Under normal circumstances, the spring force keeps the valve closed on the valve seat. When the upward pressure exceeds the downward spring force, the valve is lifted and excess steam is released into the atmosphere.

Steam Stop Valve

To stop and regulate steam flow from the boiler to the distribution lines, a steam stop valve is connected to the boiler. To prevent back-flow of steam into the boiler, the main steam stop valve on the boiler is kept closed. The steam stop valve flange is bolted to the top of the steam drum.

The main body of the valve is made of cast iron, and the valve seat is made of gunmetal. The spindle is connected to the valve on one end and the handle wheel on the other via a yoke/Gland nut and gland packing.

The handwheel is used to turn the valve. The rotating handwheel, in turn, rotates the spindle, raising the valve and allowing steam to flow.

Auxiliary steam Stop Valve, a separate steam line provided by the boiler for the small auxiliary system, is supplied via this valve in most steam systems on vessels. The valve is smaller in size and is typically non-return.

Vent Valve

To vent air from the steam drum during boiler startup, a vent valve is installed on the boiler shell. These vent valves are also useful during boiler shutdown because they allow fresh air to enter the boiler drum and prevent it from collapsing under pressure. A vent valve can also be used at the start to release/dump moist steam.

Pressure Gauge

To indicate the inside pressure of the steam drum and superheater, pressure gauges are installed. These gauges are mounted on the front top of the boiler shell and display pressure in bars. A siphon tube connects one end of a closed-section bourdon tube to the steam space.

The tube itself is filled with water to prevent steam from entering the pressure gauge. The pointer is linked to the spindle’s threaded gear. When pressure is applied to the bourdon tube, it becomes circular, turning the spindle. This causes the pointer to move along with the gear, representing the boiler pressure.

Feed Check Valve

A feed check valve is a non-return valve installed just below the normal water level on the boiler shell. It controls the flow of feed water, limiting backflow to the feed pump. For remote operation, these valves are usually equipped with an extended spindle.

These valves’ inlet and outlet points are subjected to different pressures. When the feed pump is turned on, sufficient pressure is created at the valve’s inlet. When the inlet pressure exceeds the outlet pressure, the valve is lifted, allowing water to enter the boiler.

Water Level Indicator

A pair of water level indicators are mounted directly to the boiler shell, with an additional remote reading gauge mounted in an accessible location. They are installed on the front end of all boiler types and display the water level in the boiler drum. It is made up of a glass tube with three separate valves (Steam valve, water valves, and drain valve).

The steam and water valves separate the glass tube from the boiler steam and water. In contrast, a drain valve is used to drain water from a glass tube. In the event of glass rapture/failure, a metal ball is provided on the waterside of the gauge glass to prevent subsequent accidents and water loss.

Normally, both the steam and water valves are open, allowing the water and steam pressures to balance. In the event that the reading is incorrect, we must blow through by closing the water valve and opening the drain valve.

A strong blow indicates that the steam valve is clear; repeat the procedure with the steam valve closed and the water valve open. The presence of strong blow-off steam with a hissing sound indicates that the water valve is open. Close the drain valve and allow the water to fill in before slowly opening the steam valve to equalize the pressure.

Fusible Plug

The threaded gunmetal cylinder with a conical plug and tappet hole drilled into it is known as a fusible plug. This hole is then filled with a low melting point alloy, such as tin. The plug can be either fire or steam actuated and installed over the combustion chamber.

Under normal circumstances, one side of the plug is exposed to high temperatures while the other is submerged underwater and thus kept cool. This low melting point alloy will not melt until submerged and will thus remain intact even in extreme conditions.

If the water level rises to a safe level and the plug tip comes into contact with steam, the tin alloy will melt, exposing the combustion chamber to steam. Since the steam is a poor coolant and convection medium, the tin alloy cannot transfer heat to it, causing it to melt. This sudden injection of steam into the furnace will put an end to the combustion and protect the boiler from damage.

Blow-Down Valve

Location: Blow down is a critical boiler mountings that is located at the bottom of the boiler.

Function: To empty the boiler as needed and to remove any mud, scale, or sediments that have accumulated at the bottom of the boiler.

When chloride levels become extremely high, it is used to completely empty a boiler for cleaning or to treat the boiler’s water.

Scum Blowdown Valve

Location: This boiler mounting is installed on the furnace or firebox’s crown plate.

Function: To extinguish the fire in the boiler’s furnace when the level of water in the boiler falls to an unsafe level, thereby avoiding an explosion caused by overheating of the furnace plate.

A shallow dish type system installed at ordinary water level that allows floating impurities, oil foaming, and other surface effects to be removed.

Sampling Connection /Salinometer Valve

Location: Location: A sampling water valve arrangement is typically equipped with a cooler in sequence so that water samples can be collected at any time for feed water testing.

Function: Water salinity tests.

Automatic Feed Water Regulator

Location:A vital device that is installed in the feed line.

Function: The automatic feed water regulator is one of the most important boiler mountings for ensuring the proper level of water in all load conditions. Multiple feed element water control systems are used in boilers with high evaporation rates.

Whistle Valve

If the ship has a steam whistle, steam is supplied directly from the boiler through a small non-return valve known as a whistle valve.

Low-Level Alarm

Function: A device used to generate audible low water level conditions.

Soot Blowers

Function: Soot blowing and pipe surface combustion products are both required functions. It runs on steam or compressed air.


Function: The boiler is outfitted with multiple manhole gates that allow the crew to inspect, clean, and maintain the boiler tubes and inner components.

Location: Typically, one gate is installed in the steam drum and one in the water drum.

Mud Box

Function: The mud box in the boiler collects mud (muddy impurities) from the water drum.

Location: Fitted at the bottom of the water drum.

TDS Sensor And Sample

Function:This system is now installed in the majority of modern boilers to provide continuous monitoring of total dissolved solids in boiler water. If the true value exceeds the setpoint, the sensor generates an audio-visual alarm.

A manual blowdown is used to introduce fresh feed water into the system in order to reduce total dissolved solids.

Estela Pfeiffer