Pressure Controls

Boiler Pressure controls are devices that control the operating pressure of the boiler. Steam boilers typically operate off pressure controllers. Some of these controllers are also safety devices that make sure that you do not go above a certain set point and will shut down your boiler/burner in cases where you exceed that set point. Brands such as Honeywell, Dwyer, Siemens, Johnson Controls, Ashcroft are common and we stock a wide range of those brands.

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Honeywell Boiler Pressure Control

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What are Pressure Controls & What is their function?

Pressure controls keep boilers safe and efficient 

Boilers use heat to convert water into pressurized steam that, in turn, gets work done. However, that steam must be carefully monitored and managed; pressure controls are used to tell the boiler control system or boiler operator the operating pressure of the boiler, so it can stay within its designed limits while delivering the most for every fuel dollar. 

Different Types of Pressure Controls & How To Choose

There are three types of pressure controls found in a typical boiler system: operating controls, high-limit controls, and proportioning controls.

Operating Controls

A boiler’s operating controls are the series of sensors and gauges that create a feedback loop that keeps the boiler from exceeding its safe limits. Operating controls are set to a specific temperature and pressure based on the boiler’s design; if the boiler exceeds the set pressure or temperature, the operating controls shut the boiler down. 

High-Limit Controls

A high-limit control serves primarily as a backup failsafe to the operating controls. If the boiler’s pressure starts to exceed safe limits, for example during a sudden demand surge, the high-limit control will shut down the boiler and alert the operator. Unlike operating controls, though, high-limit controls must be reset manually. This is to ensure that any potentially hazardous condition or malfunction has been addressed before the boiler resumes normal operation. 

Proportioning Controls

Proportioning controls adjust boiler firing in small increments as the target pressure is approached and reached. By adjusting slowly rather than simply turning the boiler completely on or off, proportioning controls let the boiler operate closer to its specified pressure limits while creating maximum efficiency. 

The Role Pressure Controls Play in a Boiler

When a boiler is operating at the correctly rated pressure and temperature, also known as “firing at rate”, it is at its most efficient. Pressure controls allow operators to monitor and fine-tune performance to make sure the boiler is at a rate to maximize every fuel dollar.

what are the Effects of a Bad Pressure Control?

If a pressure control goes bad, it can cause the boiler’s pressure levels to exceed safe limits. This can waste fuel, cause damage to the boiler, and create a safety hazard. 

If operating controls fail, they will cause the high-limit controls to trip frequently. This is unsafe and must be addressed immediately. 

Things to Consider about pressure control:

  • Operating controls don’t actually set the boiler’s correct operating temperature. They are a series of cut-off switches that shut the boiler down if it exceeds safe pressure limits.
  • The operating controls are the first line of defense against high pressure, but they aren’t the only ones. Even the best boiler control system needs backup pressure cut-offs.

Helpful Resources

Relevant WARE Videos on Pressure Controls

Understanding Boiler Pressure Controls

Pressure Control Episode 3: Operating Pressure Control

Pressure Control Episode 2: Modulating Control

Pressure Control Episode 4: High Limit Control

Level Controls for Lower Pressure Boilers

What Does the Low Fire Hold Switch Do? Pressure Control Series Episode Five

Differential Pressure Transmitter Basics

Back Pressure

Explore over 750+ explanatory videos on boilers and boiler systems on our Youtube channel. Our videos can help you quickly grasp complex boiler topics. Watch more here!

Relevant WARE Blog Articles on Pressure Controls

Monitoring Your Boiler Room

Understanding Boiler Pressure Controls

Today’s Lesson in Physics: The relationship between steam pressure and temperature

Under Pressure For A Test

Our informative and educational blog content can help you gain a deeper understanding of the boiler room. Read more here!

Technical Documents

Rental Contingency Plan

Formulas and Measurements

Pressure Controls FAQ

How does an operating control system work?

Operating controls can either use a microswitch or a mercury bulb to control boiler operation based on internal pressure. When the pressure exceeds a certain limit, the microswitch or mercury bulb switch will trigger another switch to reduce or cut off the boiler’s burners. 

Where do I set my pressure control limits?

Pressure controls are not set for the desired operating pressure of a boiler. Instead, they’re set higher, to allow the boiler to fire safely as long as possible under sudden load. If your boiler does not specify a manufacturer’s recommended highest safe limit, consult a WARE expert to make sure your pressures are set correctly.