The Siemens QVE1902.025 is a thermal (calorimetric) flow switch designed specifically for monitoring liquid flow in HVAC systems. It operates on the calorimetric principle, where a heated sensor element is cooled by the flowing medium. The resulting temperature difference is converted into a switching signal. This technology ensures reliable operation without any moving parts, making the device virtually maintenance-free and resistant to impurities in the medium.

Key Features

• Reliable Flow Monitoring: Provides accurate flow/no-flow detection for water and other liquids in HVAC applications.
• Simple Adjustment: The switching point can be manually set to either normally open (NO) or normally closed (NC) using the adjustment screw on the device.
• Robust Design: The brass body and IP65-rated enclosure ensure durability and protection against dust and water jets, making it suitable for demanding environments.
• Easy Installation: The G1" internal thread connection allows for straightforward integration into DN25 pipelines. The housing can be rotated 360° for flexible cable routing.
• Versatile Compatibility: Suitable for all liquid media except ammonia, with a wide temperature range of -20°C to +100°C.
• No Maintenance Required: The calorimetric measuring principle eliminates mechanical wear, reducing lifecycle costs.

Technical Specifications

• Power Supply: Not required (passive switch).
• Switching Output: Potential-free SPST contact, 1 A at 230 V AC or 48 V DC.
• Switching Capacity: Max 26 VA (AC) / 20 W (DC).
• Electrical Connection: 1.5 m PVC cable (0.5 mm²).
• Housing Material: Brass (valve body), plastic (cover).
• Ambient Temperature (Operation): 0°C to +70°C.
• Storage Temperature: -20°C to +70°C.
• Weight: Approx. 0.39 kg.
• Standards & Certifications: CE, RoHS.

Installation Requirements

To ensure accurate switching behavior, a calming section of 10 times the pipe diameter must be maintained both before and after the installation point. The arrow on the switch body must point in the direction of flow. Installation can be performed in horizontal or vertical piping. Greases or oils must not be used for sealing the threads.

Applications

The QVE1902.025 is ideal for use in HVAC plants to monitor liquid flow in:

• Refrigeration systems (evaporators, condensers).
• Heat pumps.
• Heating systems (boilers, heat exchangers).
• Cooling circuits and industrial process cooling.
• Pump dry-run protection.