The 01APS-50U.1 is a Belimo differential pressure switch for monitoring overpressure, vacuum, and differential air pressure in HVAC and energy management systems. Pressure range is 0.20 to 2.00" w.c. (50 to 500 Pa), with ±2.5% (min ±0.02" w.c. / 5 Pa) repeating accuracy and a single SPDT contact rated SPDT, max 1.0 A @ 250 VAC. The setpoint is adjustable across the full range using the internal scale; reset is automatic when the pressure returns to the normal side of the setpoint plus the switching differential. Supplied as a 45-pack carton for fleet, OEM, and bulk-stocking applications — same product as the single-unit 01APS-50U, packaged for volume.
Filter clog detection on standard residential and light-commercial AHUs, fan proving across small belt-drive fans. The Low/Mid (0.20–2.00" w.c.) range covers the most common applications in this band; if your target setpoint sits outside this range, see the comparison FAQ below for selection guidance across all four 01APS variants.
This is the 45-pack bulk carton. For a single unit, see 01APS-50U — same product, packaged for individual sale.
Key Features
Field-adjustable setpoint anywhere across the 0.20 to 2.00" w.c. range using the internal scale. Switch automatically resets when pressure returns to the normal side of the setpoint plus the switching differential (20 Pa (~0.08" w.c.)). No manual reset required after a trip event.
SPDT, max 1.0 A @ 250 VAC — line-voltage capable, suitable for direct interlock with motor starters, contactors, and BAS digital inputs. Fan proving, filter alarm, and damper end-switch wiring all work without an interposing relay.
Rated for minimum 1,000,000 switching operations, with ≤±15% deviation over 250,000 cycles per EN 1854. Burst pressure rating of 40" w.c. (10 kPa) provides margin against transient pressure spikes.
2 m (6.5 ft) of PVC sensing tubing, 2 plastic duct connectors (pitot tubes), mounting screws, and a 1/2" NPT conduit adapter all ship in the box. No separate parts pull required for a standard installation.
Sealed PA 6.6 housing with PS top cover. NEMA 13 rating suitable for indoor mechanical room mounting where exposure to oil, coolant, and non-corrosive liquids may occur.
Industry-leading factory warranty backed by Belimo's worldwide service network.
Technical Specifications
| Specification | Detail |
|---|---|
| Sensor Style | Differential pressure switch with adjustable setpoint and auto reset |
| Measured Value | Differential air pressure |
| Sensing Method | Diaphragm-actuated mechanical switch |
| Measuring Fluid | Air, non-combustible and non-aggressive gases |
| Measuring Range (in. w.c.) | 0.20...2.00" w.c. |
| Measuring Range (Pa) | 50 to 500 Pa |
| Repeating Accuracy | ±2.5% (min ±0.02" w.c. / 5 Pa) |
| Switching Differential | 20 Pa (~0.08" w.c.) |
| Burst Pressure | 40" w.c. (10 kPa) |
| Long-Term Stability | ≤±15% deviation over 250,000 cycles per EN 1854 |
| Service Life | minimum 1,000,000 switching operations |
| Output | SPDT, max 1.0 A @ 250 VAC changeover (single-pole double-throw) |
| Reset | Automatic — switch returns to normal when pressure clears the setpoint plus differential |
| Application | Air filter clog detection, fan proving, airflow verification, room pressurization monitoring |
| Mounting | Vertical orientation recommended; horizontal acceptable (switching point ~20 Pa higher); upside-down installation not permitted |
| Pressure Connections | 6 mm hose barbs (high and low pressure) |
| Cable Entry | 1/2" NPT conduit adapter included; cable gland with strain relief, ø6...8 mm |
| Electrical Connection | Terminal block, 0.5–1.5 mm² wire |
| Housing | Bottom: PA 6.6; Top cover: PS |
| Enclosure Rating | NEMA 13 / IP54 (UL Enclosure Type 13) |
| UL Approval | ETL listed per UL 508, CSA C22.2 No. 14 |
| Certification | IEC/EN 60730-1, CE Marking, EN 1854 (long-term stability) |
| Quality Standard | ISO 9001 |
| Ambient Temperature | -4 to 140°F (-20 to 60°C) |
| Fluid Temperature | -4 to 140°F (-20 to 60°C) |
| Storage Temperature | -40 to 185°F (-40 to 85°C) |
| Power Required | None — switch is electromechanical (the SPDT is wired into your control circuit power) |
| Package | 45-pack bulk carton (single product per unit; supplied 45 to a carton) |
| Manufacturer | Belimo |
| Manufacturer Part Number | 01APS-50U.1 |
| Warranty | 5-year factory warranty |
What's In the Box
- 45 × 01APS differential pressure switch in NEMA 13 housing
- 45 × 2 m (6.5 ft) PVC sensing tubing
- 45 × 2 plastic duct connector pitot tubes
- 45 × Mounting screws
- 45 × 1/2" NPT conduit adapter
Each switch in the carton ships with its own complete install kit — tubing, duct connectors, screws, and conduit adapter. No separate parts pull required.
Compatible Accessories
Documentation
Frequently Asked Questions
What is a differential pressure switch and what is it used for?
A differential pressure switch monitors the pressure difference between two points in an air system and trips a switch when that difference crosses an adjustable setpoint. The most common HVAC uses are: (1) filter clog detection — pressure rises across a filter as it loads with dust, switch trips when pressure exceeds the dirty filter setpoint; (2) fan proving — switch closes when fan develops static pressure, interlocked with the BAS to confirm fan is actually running; (3) airflow verification across coils, dampers, and other components.
What pressure range does the 01APS-50U.1 cover?
This SKU covers 0.20 to 2.00" w.c. (50 to 500 Pa) with ±2.5% (min ±0.02" w.c. / 5 Pa) repeating accuracy and a 20 Pa (~0.08" w.c.) switching differential. Choose this range when your target setpoint sits inside that band — for example, a typical dirty-filter alarm at 1.0" w.c. on a residential AHU sits squarely inside the 0.20–2.00" w.c. range of the 01APS-50U.
How do I choose between the four 01APS pressure ranges?
Pick the range whose middle covers your target setpoint with margin on both sides. Belimo's four 01APS ranges are: 01APS-50R (0.08–1.20" w.c., low — fan proving, room pressure); 01APS-50U (0.20–2.00" w.c., standard residential and light-commercial filter alarm); 01APS-501 (0.80–4.00" w.c., commercial AHU filter alarm and medium-static fan proving); 01APS-504 (2.00–10.00" w.c., high-static commercial AHUs and large-fan total static). Setpoint accuracy improves as you move up in range — 01APS-50R is ±5%, while 01APS-501 and 01APS-504 are ±1%.
How does it wire into my BAS or motor starter?
The 1× SPDT (single-pole double-throw) provides three connections: COM (common), NO (normally open), and NC (normally closed). Filter alarm: COM to NO, monitored as a digital input — closes when pressure exceeds setpoint. Fan proving: COM to NO, interlocked with motor starter — closes when fan develops static, indicating successful start. Rated SPDT, max 1.0 A @ 250 VAC: line-voltage capable for direct interlock without an interposing relay, or use as a low-voltage BAS input.
How do I install the sensing tubing?
Run the included 6.5 ft of PVC tubing from the high-pressure tap to the H port on the switch and from the low-pressure tap to the L port. For a filter clog application: H = upstream (dirty side) of filter, L = downstream (clean side). For fan proving: H = discharge of fan, L = open to mechanical room (or supply duct upstream of fan). The two plastic pitot duct connectors mount through the duct wall using the included screws.
What installation orientation is required?
Vertical orientation with pressure ports facing downward is recommended and is the orientation Belimo uses to specify the switching point. Horizontal installation with the pressure ports facing upward is acceptable but shifts the switching point ~20 Pa higher (~0.08" w.c.) — adjust the setpoint accordingly. Upside-down installation is not permitted under any circumstances.
What's the difference between the 01APS-50U and the 01APS-50U.1?
Same product, different packaging. 01APS-50U is a single unit; 01APS-50U.1 is a 45-unit bulk carton (each switch in the carton ships with its own complete install kit). Bulk carton pricing works out to approximately 18% off the single-unit price per switch, intended for fleet maintenance, OEM, and contractors stocking trucks.
Why use a mechanical pressure switch instead of an electronic differential pressure transmitter?
Three reasons: (1) Cost — a mechanical switch is significantly less expensive than an analog DP transmitter for go/no-go applications. (2) Simplicity — wires straight into a digital input or motor starter, no signal scaling or 0-10V configuration. (3) Power independence — the switch is electromechanical; only the load it switches needs power. For applications where you only need to know whether the pressure is above or below a single threshold (filter alarm, fan proving), the switch is the right answer. For continuous pressure monitoring or modulating control, use an analog DP transmitter instead.
- Sensor Type:
- Differential Pressure Switch
- Pressure Range:
- 0.20 to 2.00";Pressure Range (Pa)=50 to 500 Pa"
- Accuracy:
- ±2.5% (min ±0.02 w.c. / 5 Pa)"
- Switch:
- (1)SPDT
- Switch Rating:
- 1.0 A @ 250 VAC
- Reset:
- Automatic
- Output Signal:
- SPDT Switch (no analog signal)
- Display:
- No Display
- Setpoint:
- Adjustable Setpoint
- Override:
- No Override
- Supported Protocols:
- None (dry contact)
- Enclosure:
- NEMA 13 Enclosure
- Package:
- 45-Pack Carton
