20-300 Pa adjustable pressure monitoring for air filters, airflow, fan-belt condition and HVAC pressure supervision.
The Siemens QBM81-3 is a mechanical differential pressure switch for air and non-corrosive gases in ventilation and air-conditioning systems. Its 20-300 Pa setting range supports filter monitoring, airflow proving, fan-belt fault detection, and positive or negative pressure supervision in air ducts, clean rooms and kitchens.
A spring-loaded diaphragm actuates a single-pole change-over contact. The setpoint is adjusted beneath the cover, while the IP54 enclosure, automatic reset and rated service life above one million switching cycles support dependable long-term HVAC operation.
| Manufacturer | Siemens |
| Complete part number | QBM81-3 (stock number BPZ:QBM81-3) |
| Official catalog evidence | Exact model listed in Siemens SiePortal and Siemens technical documentation |
| Lifecycle classification | No exact official PLM lifecycle wording was confirmed; no lifecycle category is assigned |
| Product type | Mechanical differential pressure switch |
| Pressure range | 20-300 Pa; 0.2-3 mbar; 0.08-1.2 inH₂O |
| Permitted media | Air and non-corrosive gases |
| Switching contact | Single-pole change-over, potential-free contact |
| Contact rating | AC/DC 24 V, minimum 0.01 A; AC 250 V, maximum 5 A resistive / 3 A inductive |
| Maximum unilateral overload | 7500 Pa |
| Reset | Automatic |
| Service life | More than 1,000,000 switching cycles |
| Housing protection | IP54; protection class III |
| Ambient temperature | -30 to +85 °C |
| Pressure connections | Male, 6.2 mm diameter |
| Electrical connection | 3 screw terminals; PG11 cable gland |
| Dimensions | 81 x 90 mm |
| Supplied accessories | Two duct adapters, fixing screws and 2 m PVC tubing |
Signals rising pressure drop across HVAC filters so maintenance can be planned before airflow is restricted.
Confirms fan-generated pressure and airflow in ventilation ducts and can indicate a damaged fan belt.
Supports positive or negative pressure monitoring for clean rooms, kitchens and comparable controlled spaces.
Siemens currently lists QBM81-3 in its official catalog and maintains valid technical documentation for the exact model. Because no exact manufacturer PLM lifecycle term was confirmed on the reviewed official pages, this product page does not label the device Active, Classic, Obsolete or Discontinued. Availability and replacement planning should be checked against the current Siemens catalog at the time of order.
Send the installed model, setpoint, contact load and application details for stock verification, warranty information and global delivery support.
Practical support for identification, compatibility review, sourcing coordination and global delivery.
We compare the 20-300 Pa range, contact load, medium and installation method with your HVAC duty.
Part number, housing, terminals, pressure ports and supplied accessories can be reviewed before dispatch.
Stock verification, warranty terms, export packing and global shipment options are coordinated for your order.
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