Siemens QPD Series

Series Overview

The Siemens QPD Series consists of gas pressure switches designed for monitoring fuel gas pressure in industrial and commercial burner systems. These switches serve as safety interlock devices that verify whether gas pressure remains within a defined safe operating range before and during combustion. If the gas pressure deviates from the configured threshold, the QPD switch interrupts the burner safety circuit, preventing unsafe ignition or continued operation.

Within a combustion control architecture, the QPD Series is positioned as a fuel supply monitoring component in the burner safety chain.

Functional Role in Burner Systems

In a typical industrial gas burner configuration, the QPD gas pressure switch works alongside:

• Burner control units (e.g., LME / LDU / LMV systems)
• Gas solenoid valves
• Air pressure switches (e.g., QPL Series)
• Flame supervision systems

Before ignition, the burner controller confirms that gas pressure is within acceptable limits through the QPD switch. If gas pressure falls below (or exceeds, depending on configuration) the defined threshold:

1. The safety circuit is opened
2. Fuel supply is interrupted
3. The system enters lockout mode

This ensures compliance with combustion safety requirements.

Typical Applications

QPD Series pressure switches are commonly applied in:

• Industrial gas burners
• Commercial gas-fired boilers
• Process heating systems
• Furnace and oven combustion systems
• Dual-fuel burner installations (gas monitoring side)

They are particularly critical in installations where stable gas supply pressure must be continuously verified.

Core Technical Characteristics

Although individual models vary, the QPD Series generally includes:

• Gas pressure monitoring capability
• Adjustable switching thresholds
• Mechanical safety switching mechanism
• Robust industrial housing
• Compatibility with standard burner control safety circuits
• Designed specifically for fuel gas applications

Unlike generic pressure switches, QPD units are calibrated for combustion gas monitoring rather than air systems.

Model Differentiation Logic

Different QPD models are defined primarily by:

• Pressure monitoring range (low-pressure or higher range versions)
• Switching configuration (normally open / normally closed)
• Electrical contact rating
• Mounting and connection design

Model selection depends on:

• Burner capacity
• Required minimum or maximum gas pressure limits
• National safety code requirements
• Gas supply characteristics

Each model is engineered to meet specific combustion system design needs.

Safety Chain Positioning

Within a combustion safety architecture, the QPD Series performs:

Gas Supply Verification → Safety Interlock → Ignition Permission

Typical safety sequence:

1. Gas pressure verified via QPD switch.
2. Airflow verified via air pressure switch (e.g., QPL).
3. Burner control unit initiates ignition sequence.
4. Continuous supervision maintained during operation.
5. If gas pressure deviates from defined limits, the system shuts down immediately.

This positioning classifies the QPD Series as a safety-relevant fuel monitoring device.

Integration Within Siemens Combustion Systems

In Siemens burner system architecture, the QPD Series complements:

• Burner control units (LME / LDU / LMV platforms)
• Gas valve assemblies
• Air pressure supervision devices
• Flame monitoring equipment

Together, these components form a structured, fail-safe combustion control system.