The Ins and Outs of Air Proving Switches

Air proving switches, also known as air pressure switches or combustion air switches, play a vital role in boiler safety and performance. These ingenious devices monitor air pressure and airflow to ensure proper ventilation and prevent dangerous buildup of unburned fuel.

For commercial and industrial facilities that rely on boilers for steam or hot water, understanding air proving switches is essential. Our company JET Hotel Solutions ( will be a perfect helper for you.

What Exactly is an Air Proving Switch?

An air proving switch is a type of differential pressure switch installed on forced draft burners. It monitors the difference in air pressure between two points in the airflow path. One port connects to the intake before the blower and the second port attaches downstream, typically right before the burner.

The air proving switch serves two key functions:

Proving Airflow During Purge Cycles

Before ignition, boilers first go through a purge cycle to flush out any residual fuel or combustible gases. This requires a minimum number of air exchanges determined by the boiler manufacturer. The air proving switch verifies this proper airflow for the prescribed duration, signaling to the flame safeguard system when it’s safe to proceed with ignition.

air pressure switches or combustion air switchesMaintaining Proper Combustion Air

Once running, the air proving switch continues monitoring pressure differential to confirm adequate airflow for proper combustion and ventilation. If the pressure drops below the switch’s setpoint, it will shut off the burner to prevent issues like flameouts, explosions, or meltdowns due to insufficient air.

Why Air Proving Switches Are Vital

Air proving switches offer several layers of critical protection:

Preventing Fuel Buildup – By verifying complete air exchanges during purge cycles, air proving switches prevent any unburned oil or gas from accumulating in the combustion chamber. This mitigates the chance of uncontrolled ignitions.

Avoiding Incomplete Combustion – With insufficient airflow, boilers experience incomplete combustion, creating carbon monoxide and soot. Air proving switches shut down operation before this becomes hazardous.

Protecting Equipment – Inadequate ventilation leads to thermal stress, warped components, and damage from excessive heat. Air proving switches minimize this by keeping airflow within design limits.

Monitoring Blower Function – If the air pressure differential drops, it likely indicates a problem with the blower fan. The air proving switch catches this malfunction early before damage occurs.

Companies like Jet Hotel Solutions provide air proving switches designed for the demands of commercial boiler rooms. Their switches combine robust pressure sensors with programmable logic to offer customizable protection.

Types of Air Proving Switches

With such an important safety role, air proving switches must be precisely selected for the specific boiler and application. There are two main categories:

Setpoint switches simply trigger when the pressure reaches a preset threshold, either during purge cycles or running operation. A wide range of actuation setpoints are available.

Differential switches measure the difference between the intake and outlet ports. They maintain this within an acceptable range throughout operation. The setpoint is the allowable differential rather than an absolute pressure.

Within these types, the switches feature different pressure measurement mechanisms:

Diaphragm – Uses an elastic diaphragm that deforms proportionally to the applied air pressure. Useful for applications up to 150 psi.

Piston – A cylinder and spring-loaded piston actuate when pressure exceeds the spring resistance. These robust switches handle up to 6000 psi.

Bellows -Pressure causes expansion of a bellows capsule which actuates the switch. Bellows models can withstand pressures up to 15,000 psi.

Selecting the Proper Switch

Choosing the right air proving switch requires matching the boiler’s specifications and air handling system. Key factors include:

Pressure range – The actuation pressure must be within the burner’s airflow range

Setpoint tolerance – Tighter pressure tolerances improve performance but cost more

Maximum temperature – Durability required for the boiler and exhaust temperature

Switch type and mechanism – Based on required pressure range and reliability

It’s also critical to partner with qualified technicians to install air proving switches properly. This ensures the ports connect at the right locations to accurately measure differential pressure. Ongoing maintenance like annual testing and calibration checks keeps air proving switches functioning properly for years.

How Air Proving Switches Work

The inner workings of air proving switches consist of an actuator coupled to electrical contacts. Here is a step-by-step look:

  1. As the blower runs, air pressure builds and is applied to the diaphragm, piston, or bellows.
  2. This pressure produces a force that compresses the actuation spring.
  3. When the spring compresses sufficiently from the preset pressure, the attached lever pivots.
  4. This lever actuation toggles the electrical contacts either closed or open, depending on the switch mechanism.
  5. For setpoint types, closing the contact signals the flame safeguard system.
  6. For differential switches, the contact state confirms the pressure difference is in range.
  7. If air pressure drops outside the set limits, the actuation spring extends and returns the lever and contacts to their normal state. This triggers shutdown actions by the boiler control system until proper airflow resumes.

By converting air pressure into physical movement and an electrical control signal, air proving switches offer a straightforward and reliable method of monitoring boiler ventilation.

Maintaining Peak Performance

Air proving switches play such a crucial safety role that diligent maintenance is essential. Here are important practices facilities should follow:

Annual Testing – Use an accurate pressure source to verify actuation at the proper setpoints for both increasing and decreasing pressure.

Calibration Checks – Confirm the pressure switch is calibrated and still within OEM specifications. Recalibrate if readings are off by more than 2-3%.

Visual Inspection – Check for visible dirt or debris on the pressure ports which can affect sensing accuracy.

Filter Changes – For switches with inlet filters, replace per manufacturer guidelines, usually around annually.
Control Loop Verification – Ensure pressure tubing remains intact without leaks or obstructions which alter readings.

By proactively maintaining air proving switches, facilities can keep them working properly for the long haul. Catching any issues early on also prevents potentially dangerous boiler malfunctions. For mission-critical applications, redundancy using multiple networked switches adds another layer of protection.

As essential as they are complex, air proving switches allow boiler operation that is both efficient and safe. With proper selection, installation, and maintenance from experienced companies like Jet Hotel Solutions, these specialized pressure switches monitor and control airflow flawlessly year after year. Facilities that take the time to understand air proving switches gain peace of mind knowing potential combustion hazards have been minimized.

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