Why Does Boiler Pressure Drop: Detailed facts

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This article answers the question- why does boiler pressure drop? A boiler is a device used to procude steam or heat the working fluid that is used to generate power in further steps.

The fluid used inside the boiler does not necessarily boil. The heated fluid is further used in many applications like generating electricity, cooling and sanitation. In this article we shall study more about boilers and related questions.

What is a boiler?

As stated above, a boiler is a device used for heating the working fluid so that it can be used for further applications.

Even though the name suggests that the working fluid will boil but is not necessarily true. The working fluid can be used for further applications without reaching its boiling point. In next section we shall see the heat sources from which the boiler gets heat.

Sources of heat

There are many heat sources from which the boiler takes heat. These heat sources provide the necessary heat energy to the working fluid. This absorbed heat energy is then utilised or is converted to another usable form of energy.

The commonly used heat sources are burning of coal, oil, natural gas. Some boilers which are also called as steam generators produce heat with the help of nuclear fission. A nuclear fission is a process in which the atom splits to emit a huge amount of energy. In some applications Carbon Monoxide is also used as a heat source.

why does boiler pressure drop
Image: Boiler

Image credits: Old Moonraker at en.wikipedia, Steam Boiler 2 English version, CC BY-SA 3.0

Materials used for making boilers

The boilers come in variety of materials. They mainly depend on the applications and the working temperature of the boiler. The next section discusses about the materials used for making boilers.

Pressure vessels of a boiler are generally made of steel and wrought iron. Stainless steel is not used in wetter parts of the boiler due to the risk of corrosion. In some steam models, Copper and Brass are used because these materials facilitate easy fabrication in small sized boilers.

Why does boiler pressure drop when heating is on?

When the heating is on the expansion of the steam takes place, due to this the pressure of the steam keeps on increasing.

Due to the increased pressure, the steam starts exerting pressure on the walls of boiler, if there is a leak in the boiler the boiler pressure will keep on decreasing. Another reason for the drop in boiler pressure is due to releasing of air or water to the radiator when bleeding it.

Why does boiler pressure drop overnight?

The main reason for pressure drop inside a boiler is leak. The leaks can take place in many forms. Sometimes it is done on purpose and sometimes it happens unknowingly.

The reasons of pressure drop may include leak in the pressure relief valve, a problem in the expansion vessel, air inside the system or a leak in the pipework itself.

Can a boiler lose pressure without a leak?

In most of the cases, almost 99%, the boiler loses pressure due to leaks only. There may be leaks in pressure relief valve, pipe work or in expansion vessel.

If there is no leak then there can be a fault inside the boiler or the pressure gauge must be faulty. Other than this, when the air or water is bled in the radiator, the pressure inside the boiler will decrease.

Does boiler pressure drop in summer?

The boiler pressure depends on the water content flowing through the pipelines. Generally in summers, the boiler pressure is low.

This happens due to the fact that the water content inside the pipelines is lesser because the boiler is kept idle for a longer time. A lower boiler pressure indicates that the amount of water being circulating in the system is dropped.

Why does boiler pressure drop in winter?

Boilers are subjected to additional pressure after they are kept idle for a long time in summers. When these boilers are put on to use during winters, the pressure on the boilers increase drastically.

Otherwise the boiler will lose pressure when the boiler has leak inside the relief valve or pressure tanks. When the cold water is heated the molecules of water expand in a random manner, if there is a leak the pressure will keep on decreasing from the boiler.

Types of boilers

Many types of boilers can be used to provide the heat to the system. The type of boiler that is to be used depends on the type of application, quantity of heat to be produced and the working fluid.

The different types of boilers are given in the list below-

  • Gas boilers
  • Oil boilers
  • Husk fired boilers
  • Water tube boilers
  • Electric boilers
  • Biomass boilers
  • Waste heat boilers
  • High efficiency boilers

Accessories used in boilers

Boilers come with many accessories and fittings. The list below shows the different accessories used in boilers-

  • Pressuretrols – It is used to control the pressure inside the boiler. Usually the boilers have three types of pressuretrols- A manual-reset pressuretrol, operating pressuretrol and a modulating pressuretrol.
  • Safety valves – It is used to relieve excessive pressure. Excessive pressure can lead to explosion. Using of safety valves ensure safety from explosions. As the safety valves release the excess pressure, hence no excess pressure no explosion.
  • Water level indicators – The name itself suggests us about its functions. The water level indicators tells us about the level of fluid. Other names used are sight glass, water gauge or water column.
  • Bottom blowdown valves – The blowdown valves provide a means for removing solid particles or sediments that settle at the bottom of boiler. These valves are installed at the bottom of boiler and occasionally used to remove the particulates by using the pressure from the boiler.
  • Continuous blowdown valve – This valve allows the water to flow out continuously. The main purpose of this valve is to prevent water in the boiler to become saturated salts with dissolved salts.
  • Trycock – This is used to find the water level inside the water boiler. This is generally used in water boilers.
  • Flash Tank – The blowdown comes to this vessel with very high pressure. Here the steam can be flashed safely and be used in a low pressure system and can also be vented out to atmosphere.
  • Hand holes: These are steel plates which allow for inspections of tubes and installation of pipes.
  • Top feed: This is used to feed water from the top of boiler. This prevents the boiler from fatigue as the thermal stresses acting on the boiler are reduced.
  • Low water cutoff: It is a safety switch that or an electrode with a safety switch that is used to turn off the burner or switch off the fuel supply to prevent it from running once the water level reduces below a certain limit. If a boiler is “Dry fired” means there is no water content in it then it can lead to catastrophic consequences.
  • Automatic heat recovery system: This recovery system allows the blowdown only when the makeup water is flowing to the boiler. This results in maximum heat transfer taking place from the blowdown to the makeup water. In this case no flash tank is needed as the temperature of the blowdown discharge is similar to the temperature of makeup water.

Read more about Does Boiler Pressure Increase, Boiler Steam Temperature and Boiler Steam Drum.