What are Boiler Mountings?- A Complete List With Functions

What are Boiler Mountings?

Boiler mountings are essential safety mechanisms designed to ensure that boilers operate securely and efficiently. Typically, there are seven primary mountings found on a boiler shell: the safety valve, steam stop valve, vent valve, pressure gauge, water level indicator, feed check valve, and fusible plug.

Each of these components plays a critical role in protecting the boiler from a range of hazards. For example, they help guard against damage caused by excessive pressure, prevent the backflow of steam, protect against shell collapse from vacuum conditions, regulate steam pressure, monitor water levels, stop feed water from flowing back toward the pump, and avoid dangerous situations such as dry running.

In this discussion, we’ll explore the various types of boiler mountings commonly used in steam boilers, taking a closer look at their construction and how they work.

It’s worth noting that improper maintenance or neglecting routine cleaning can often lead to boiler accidents or breakdowns. Without the appropriate boiler mountings in place, a single oversight can quickly escalate into a serious incident, potentially damaging both the boiler itself and its surroundings.

Consider the high lift safety valve, for instance—without it, the boiler shell could be at risk of exploding, posing significant danger to both personnel and equipment. In a similar vein, if an air vent is not available during the boiler’s cooldown process, the shell might collapse due to vacuum formation.

Particularly during cargo operations, when the demand for steam tends to increase, these mountings become even more important. They not only facilitate safer operation but also help manage the increased workload, allowing the boiler to run more smoothly and reliably.

Boiler mountings are as follows:

• Safety Valve
• Main Steam Stop Valve
• Auxiliary Steam Stop Valve
• Water level gauge glass
• Air Vent valve
• Feed check Valve
• Pressure gauge connection
• Blow Down Valve
• Scum Blow Down Valve
• Sampling Connection
• Whistle Valve
• Low Level Alarm
• Soot Blower
• Automatic Feed valve Regulator
• Manhole
• Mud box
• TDS Sensor and Sample

#1. Safety Valves

Every boiler is equipped with safety valves to prevent the risk of over-pressurization. In most cases, you’ll find three safety valves installed: typically, one is placed on the superheater, while the remaining two are mounted on the steam drum.

It’s important to note that, regardless of the boiler type, there must never be fewer than two safety valves in operation. These valves are specifically designed to open at a pressure that is 3% above the normal working pressure of the boiler, ensuring a reliable margin of safety.

Structurally, a steam safety valve usually features a cast iron body and incorporates two independent valves situated on the valve seat. These valves are linked to a lever system by way of a pivot, which is held firmly in place by a spring mechanism.

Under regular operating conditions, the tension in the spring keeps the valves tightly closed against the valve seat. However, if the pressure inside the boiler rises to a point where it overcomes the force of the spring, the valves will lift automatically. This action allows excess steam to escape safely into the atmosphere, effectively protecting the boiler from dangerous pressure levels.

#2. Steam Stop valve

A steam stop valve is an essential component attached to a boiler, designed to control and, when necessary, halt the flow of steam from the boiler to the system’s distribution lines.

Its primary purpose is to ensure that steam only moves in the intended direction and doesn’t flow back into the boiler, which is why the main stop valve is usually kept closed until steam needs to be released.

You’ll typically find the valve’s flange securely bolted to the top of the steam drum for maximum safety and efficiency.

In terms of construction, the main body of this valve is generally made from cast iron, a material known for its strength and durability. The valve seat, on the other hand, is often crafted from gunmetal to withstand the constant exposure to steam and provide a reliable seal.

The spindle—one end connected to the valve and the other attached to the handwheel—runs through the yoke (sometimes referred to as the gland nut) and gland packing, ensuring a tight fit and smooth operation.

Operating the valve is quite straightforward: turning the handwheel causes the spindle to rotate, which in turn lifts the valve and opens a pathway for steam to flow from the boiler.

It’s also common to find an auxiliary steam stop valve fitted to boilers, especially on ships or in setups with additional steam-driven systems. This auxiliary valve serves smaller auxiliary lines and is usually smaller in size than the main valve.

For safety and efficiency, these are often non-return valves, preventing any backflow of steam into the auxiliary system.

#3. Vent Valve

A vent valve plays a crucial role on the boiler shell, especially when it comes to managing air inside the steam drum during boiler startup. At the beginning of the operation, this valve allows trapped air to escape, which helps create the proper conditions for steam formation.

But its usefulness doesn’t end there. During boiler shutdown, the vent valve has another important job: it lets fresh air into the drum. This simple action helps prevent the boiler from collapsing as internal pressure drops.

You might also find the vent valve helpful when it’s time to get rid of any moist steam lingering in the system right at startup. By opening the valve, operators can clear out that initial burst of damp steam and ensure everything runs smoothly from the get-go.

#4. Pressure Gauge

Pressure gauges are installed on both the steam drum and the superheater, giving a clear reading of the steam pressure inside the system. You’ll typically find these gauges mounted at the front top of the boiler shell, where they display the pressure in bar units.

The main component here is a Bourdon tube, which has a closed cross-section and is connected to the steam space by means of a siphon tube. That siphon tube isn’t just there for show—it’s actually filled with water, acting as a barrier to prevent hot steam from reaching and potentially damaging the pressure gauge.

Here’s how it works: the pointer on the gauge is linked up to a small, threaded gear, which itself is attached to a spindle. When steam pressure builds up, it acts on the Bourdon tube, causing the tube to straighten out and turn the spindle. As the spindle turns, the gear moves the pointer along the dial, so you can see at a glance exactly what the boiler pressure is.

#5. Water Level Indicator

A pair of water level indicators is typically mounted directly onto the boiler shell, along with an extra remote reading gauge positioned somewhere more accessible for easy monitoring.

These indicators are usually installed right on the front end of any boiler, providing a clear view of the water level inside the boiler drum. At the heart of this setup is a glass tube, which is controlled by three separate valves: one for steam, one for water, and a drain valve.

Here’s how it works: The steam and water valves serve to isolate the glass tube from the boiler’s steam and water, respectively, depending on what needs to be checked or maintained. The drain valve, as the name suggests, lets you empty the water from the glass tube whenever required.

One thoughtful safety feature included on the waterside of the gauge glass is a metal ball. This is a backup in case the glass tube ever ruptures or fails. The ball moves to seal off the opening, minimizing both water loss and the risk of accidents by preventing water from instantly turning to steam and flashing out.

Under regular conditions, both the steam and water valves are left open. This allows water and steam to flow freely and reach equilibrium inside the gauge, giving an accurate reading.

But sometimes the readings might seem off. When that happens, you’ll need to “blow through” the gauge to clear any blockages. This process starts by closing the water valve and opening the drain valve.

If you get a strong burst of steam, you know the steam valve is unobstructed. Next, close the steam valve and open the water valve while the drain is still open. A strong, hissing rush of water means the water valve is also clear.

After that, close the drain valve, let the glass tube refill with water, and slowly open the steam valve to equalize the pressure once again. This ensures everything is functioning as it should, and you can rely on the gauge for accurate water level readings.

#6. Feed Check Valve

A feed check valve, which is essentially a type of non-return valve, is installed on the boiler shell just below the usual water level. Its main job is to control the flow of feed water, making sure that water can only move one way—into the boiler—and doesn’t flow back toward the feed pump.

You’ll often find these valves equipped with an extended spindle. This design choice isn’t random; it’s there so the valve can be operated remotely, making it a bit more convenient for the user, especially in larger setups.

It’s important to note that the inlet and outlet of a feed check valve experience different pressures. Here’s how it works in practice: when the feed pump kicks in, it creates enough pressure at the valve’s inlet. If this inlet pressure ends up higher than the pressure on the outlet side, the valve will lift open, letting water flow right into the boiler. If not, it stays shut, preventing any unwanted backflow.

#7. Fusible Plug

A fusible plug is essentially a threaded gunmetal cylinder, fitted with a conical plug and a tappet hole that’s filled with a low-melting-point alloy, typically tin. These plugs are available in either fire-actuated or steam-actuated types and are usually installed above the combustion chamber.

Under standard operating conditions, one end of the fusible plug is subjected to intense heat from the furnace, while the other end stays submerged in water, which keeps the alloy cool and intact. As long as the plug tip remains underwater, the low-melting-point alloy doesn’t melt—even in high temperatures.

However, if the water level drops to an unsafe limit and the plug tip becomes exposed to steam instead of water, that’s when things change. Tin alloy, being unable to effectively transfer heat to steam (since steam isn’t a good coolant), will begin to melt. This melting creates an opening that allows steam to rush into the combustion chamber.

This sudden burst of steam effectively snuffs out the combustion process, acting as a protective measure to prevent the boiler from overheating and sustaining damage.

#8. Blow-down valve

Location: The blow down valve is a crucial boiler mounting, typically installed at the lowest point of the boiler.

Function: Its main job is to allow the boiler to be emptied whenever necessary, especially for clearing out mud, scale, or any sediment that gathers at the bottom over time.

In practice, this valve is especially useful when the concentration of chlorides in the water rises too high. By opening the blow down valve, all the water can be drained out so the boiler can be properly cleaned or the water can be treated as needed.

#9. Scum blows down valve

Location: This particular boiler mounting is installed directly onto the crown plate of the furnace or firebox.

Function: Its main job is to extinguish the fire inside the boiler’s furnace whenever the water level drops to a dangerously low point. By doing this, it effectively prevents the furnace plate from overheating—a situation that could otherwise lead to a boiler explosion.

Additionally, this setup includes a shallow, dish-shaped system positioned at the standard water level. Its purpose is to help remove floating impurities, oils, and foam from the water’s surface, keeping the boiler’s operation safe and efficient.

#10. Sampling connection /Salinometer Valve

Location: A typical sampling water valve setup usually includes a cooler arranged in line. This design allows for water samples to be safely collected at any time, making it convenient to conduct feed water testing whenever necessary.

Function: This setup is primarily used to perform salinity tests on the water.

#11. Whistle valve

When a steam whistle is installed on a ship, it receives steam directly from the boiler. This steam passes through a small device called a whistle valve, which is essentially a non-return valve designed for this purpose.

#12. Low-Level alarm

Function: This device serves to detect and alert users to low water levels by emitting an audible signal whenever such a condition occurs.

#13. Soot blowers

Function: This function plays a vital role in removing soot and combustion residues from pipe surfaces. The process is typically carried out using either steam or compressed air, depending on the specific requirements and operational setup.

#14. Automatic feed water regulator

Location: This device is installed directly into the feed line, playing a crucial role in the boiler system.

Function: The automatic feed water regulator is an essential boiler fitting that helps maintain the correct water level, regardless of changes in load. In boilers where the rate of evaporation is especially high, a multi-element feed water control system is typically implemented to ensure water levels remain stable and safe.

#15. Manhole

Function: Boilers are designed with several manhole gates, which serve as crucial access points for the crew. These gates allow for thorough inspection, effective cleaning, and routine maintenance of the boiler tubes as well as internal components. Having direct access in this way makes it possible to address issues promptly and keep the system operating safely and efficiently.

Location: You’ll generally find at least one manhole gate on the steam drum and another on the water drum. This placement isn’t random; it’s intended to make the most vital parts of the boiler easily accessible when maintenance or inspection is required.

#16. Mud box

Function: The mud box in a boiler serves to collect the muddy impurities that settle out from the water inside the drum.

Location: It is positioned at the lowest point of the water drum, where these impurities tend to accumulate.

#17. TDS Sensor and Sample

Function: In most contemporary boilers, a system is typically installed to keep a close eye on the total dissolved solids (TDS) present in the boiler water. This setup uses a sensor that constantly checks the actual TDS level against a predefined setpoint. If the measured value goes above the acceptable limit, the system triggers both audio and visual alarms to alert the operator.

When high TDS levels are detected, the standard practice is to perform a manual blowdown. This process helps by flushing out some of the concentrated boiler water and allowing fresh feedwater to enter the system, which effectively lowers the overall TDS concentration.

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