The ACI DBL-205B is part of ACI's DBL Series Differential Pressure Switch family, configured for an adjustable set-point range of 0.2-2 inWC. The plastic NEMA 3 (IP54) weather-proof enclosure contains an on/off single-stage micro switch and two pressure chambers separated by a silicone diaphragm. Unlike the metal-housing AFS family, the DBL ships with a factory-calibrated linear-scaled set-point knob - the set point can be adjusted directly to the marked value without comparing to a field gauge, manometer, or magnehelic, dramatically reducing commissioning time. SPDT contact with automatic reset, 1.5A resistive load rating, and a 1,000,000-cycle life expectancy. The factory-default switching differential is +/-15% of the trip point (field-adjustable across 0.08-0.16 inWC, though ACI recommends leaving the factory default). Used in HVAC and Energy Management applications for monitoring filter blockage, proof of flow, and excessive/insufficient flow alarms. Made in USA by ACI in Middleton, Wisconsin.
This switch is best suited for low-pressure HVAC proving: light commercial filter monitoring, small-AHU fan-status verification, exhaust hood proof-of-flow, and applications where the working differential is between 0.2-2.0 inWC and finer adjustment resolution matters. The plastic NEMA 3 / IP54 enclosure makes the DBL a strong fit for outdoor/wash-down adjacent environments where the galvanized-steel AFS would corrode, and the factory-calibrated linear knob is preferred for fast field commissioning when a manometer isn't on hand. The lower load rating (1.5A resistive / 0.4A inductive) suits signaling to a BAS controller rather than direct motor switching - if you need to switch a fan motor or solenoid directly, use the AFS-460. Per ACI's published applications: monitoring filter blockage, proof of flow, prove excessive or insufficient flow, alarms and control.
Key Features
The DBL's signature feature: a factory-calibrated, linear-scaled set-point knob on the front of the enclosure. The set point can be adjusted directly to the marked value on the knob - without comparing to a field gauge, manometer, or magnehelic. Turn clockwise to increase set point. Saves significant commissioning time versus traditional pressure switches that require iterative measurement with an external manometer to confirm the trip point.
Weather-proof plastic enclosure rated NEMA 3 (IP54) - protected against falling dirt, wind-blown dust, rain, sleet, snow, and water splash. Base is glass-filled PA6.6 nylon for impact and chemical resistance; cover is transparent polystyrene for at-a-glance verification of switch state and knob position. Suitable for outdoor rooftop installations and indoor wash-down adjacent areas where the metal AFS would be subject to corrosion.
Set point is field-adjustable across 0.2-2 inWC via the linear-scaled knob. Switching differential is factory-set to +/-15% of the trip point (also field-adjustable across 0.08-0.16 inWC, but ACI recommends leaving the factory default - a smaller switching differential can cause failures and change the switch behavior outside the datasheet specification). The internal switching-differential screw should not be adjusted under live high-voltage power.
A single-pole double-throw SPDT (Form 1C) micro switch with automatic reset - the switch resets when pressure returns to the normal range. Terminal designations: 3 (Common), 2 (Normally Open), 1 (Normally Closed). On pressure increase, contact 3-to-2 closes (proving high pressure); on pressure decrease, contact 3-to-1 closes (proving low pressure). Spade-terminal connections accept maximum 16 AWG (1.5 mm²) wire. Rated 250 VAC max, 1.5A resistive (0.4A inductive).
One million cycles minimum mechanical endurance - among the highest in the industry for HVAC pressure switches. This is 100x the rating of typical manual-reset pressure switches (which trade cycle life for higher inductive ratings). The high cycle count makes the DBL well-suited for applications with frequent cycling - filter loading alarms that trip and clear multiple times daily, intermittent fan-status verification, and demand-controlled ventilation interlocks.
Two pressure chambers separated by a silicone diaphragm sense the differential between P1 (high, lower port) and P2 (low, upper port). Compatible with air and other non-combustible, non-aggressive gases. Maximum operating pressure is 40 inWC (10 kPa) - well above the operating range, providing headroom for transient pressure spikes from fan start-up or damper slam events.
Two pressure ports accept 3/16" ID (8 mm) push-on plastic or poly tubing - faster installation than the compression fittings on the AFS series. Port P1 (high pressure, +) is on the lower part of the housing; P2 (low pressure, -) is on the upper part. ACI offers the DBZ-06 duct-mount kit specifically for the DBL (two right-angle metal pitot tubes, two grommets, and 6.5 ft / 2 m of tubing) - the recommended accessory for in-duct pressure pickup.
The enclosure has a 1/2" NPT conduit knockout for code-compliant electrical routing. ACI recommends 16-26 AWG twisted-pair wires or shielded cable. Spade-terminal connections accept maximum 16 AWG (1.5 mm²) wire. All wiring must comply with local and National Electric Codes. The enclosure cover guards against accidental contact with the live switch terminal screws.
For best results, mount with the pressure port connections pointing downward (vertical orientation). If horizontal mounting is necessary, deduct 0.08 inWC (20 Pa) from the desired set point for offset adjustment. Never mount with the setpoint knob facing downward - this causes incorrect switch performance. Surface-mount via four screws through the integral bracket (do not over-tighten - deforming the housing can cause air leakage).
DBL-205 Family Selection Guide
All four DBL-205 variants share identical mechanical, electrical, and enclosure specifications - they differ only in the set-point range and switching differential. Select the variant whose range bracket includes your working set point.
| Model | Item # | Set Point Range | Switching Differential | Contact |
|---|---|---|---|---|
| DBL-205L | 105934 | 0.08-0.8 inWC | 0.04-0.08 inWC | SPDT |
| DBL-205B ← this SKU | 102423 | 0.2-2 inWC | 0.08-0.16 inWC | SPDT |
| DBL-205D | 102424 | 0.8-4 inWC | 0.4-0.8 inWC | SPDT |
| DBL-205E | 106255 | 2-10 inWC | 0.6-1.2 inWC | SPDT |
Technical Specifications
| Specification | Detail |
|---|---|
| Product Type | Differential air pressure switch, snap-acting (plastic enclosure) |
| Input Pressure Range | See ordering grid (20 inWC / 5000 Pa max input) |
| Adjustable Set Point Range | 0.2-2 inWC |
| Adjustable Set Point Switching Differential | 0.08-0.16 inWC |
| Factory-Default Switching Differential | +/-15% of trip / set point |
| Set-Point Adjustment | Linear-scaled knob (factory-calibrated; no manometer needed) |
| Contact Arrangement | SPDT (Form 1C) with automatic reset |
| Contact (Load) Rating | 250 VAC maximum, 1.5A resistive (0.4A inductive) |
| Reset Style | Automatic |
| Measured Media | Air and other non-combustible, non-aggressive gases |
| Diaphragm Material | Silicone |
| Maximum Operating Pressure | 40 inWC (10 kPa) |
| Life Expectancy | 1,000,000 cycles |
| Operating / Storage Temperature Range | -4 to 185 deg F (-20 to 85 deg C) |
| Mounting Direction | Any vertical plane (port connections pointing down preferred); horizontal mounting requires 0.08 inWC offset adjustment |
| Enclosure Material | Base = PA6.6 nylon, Cover = polystyrene (transparent) |
| Enclosure Rating | NEMA 3 (IP54) |
| Sample Line Connections | 3/16 in ID (8 mm) push-on plastic/poly tubing; ports P1 (high, lower) and P2 (low, upper) |
| Electrical Connections | Spade terminals, maximum 16 AWG (1.5 mm²) |
| Conduit Opening | 1/2 in NPT conduit knockout |
| Agency Approvals | CE, ISO 9001, RoHS2, WEEE |
| Dimensions (Diameter x Height) | 4.00 x 2.30 in (100 x 58 mm); 3.88 in deep with conduit connection |
| Weight | 0.40 lb (0.20 kg) |
| Manufacturer | ACI (Automation Components, Inc.) - Middleton, WI USA |
| Manufacturer Part Number | DBL-205B |
| Item Number | 102423 |
| Warranty | 2-Year ACI Limited Warranty |
What's In the Box
- DBL pressure switch with plastic NEMA 3 (IP54) enclosure
- Pre-installed silicone diaphragm
- Linear-scaled set-point knob (factory-calibrated)
- Cover with 1/2" NPT conduit knockout
- Integral mounting bracket (4-screw surface mount)
- Installation & Operation Instructions (ACI document I0000154)
- DBL-specific duct-mount kit: DBZ-06 (includes two metal right-angle pitot tubes, two grommets, and 6.5 ft / 2 m of tubing) - the recommended accessory for in-duct pressure pickup
- Sample-line tubing (3/16" ID plastic/poly) - A/10' TUBE, A/20' TUBE, A/50' TUBE, A/100' TUBE for longer runs
- Alternative pitot tubes (compatible via tubing): PT 3", PT 5.2", PT 7.5", PT 9.7" (foam-gasket multi-point); SPT-3.5" / SPT-8.0" (aluminum static, flat tip); VPT / VPT-8" (aluminum velocity, pointed tip)
- Pickup ports for wall/room pressure taps: A/SP-PUP, A/R-PUP, A/R2-PUP, A/O-PUP-H, A/O-PUP-V
- 1/2" conduit fitting and conduit (if used)
- Wire (16-26 AWG twisted-pair shielded cable recommended)
Documentation
Frequently Asked Questions
What is the DBL-205B used for?
The DBL-205B is a general-purpose differential air pressure switch with a plastic NEMA 3 (IP54) enclosure, used in HVAC and Energy Management applications for monitoring filter blockage, proof of flow, alarms, and control sequences. The SPDT auto-reset contact closes (or opens) when the differential pressure across the silicone diaphragm exceeds the configured set point - giving a binary "pressure OK / not OK" signal to a BAS controller, alarm panel, or interlock circuit. Can sense positive, negative, or differential air pressure depending on tubing setup.
How is the set point adjusted?
The DBL ships with a factory-calibrated linear-scaled set-point knob on the front of the enclosure. Turn clockwise to increase the set point; the knob position directly indicates the trip point on the scale - no manometer, magnehelic, or external gauge required for adjustment. This is the DBL's signature advantage over the AFS series. The adjustable set point range for this SKU is 0.2-2 inWC. Do not adjust the knob with high-voltage power connected.
How does the DBL compare to the AFS series?
Both are HVAC differential pressure switches. DBL advantages: plastic NEMA 3 / IP54 enclosure (outdoor and wash-down capable), factory-calibrated linear knob for fast commissioning without a manometer, 1,000,000-cycle life, lighter (0.4 lb vs 1.2 lb), lower cost, push-on tubing (no compression fitting). AFS advantages: galvanized steel housing for mechanical durability, higher load rating (15A vs 1.5A) suitable for direct motor switching, available with manual reset (AFS-460 series) for safety-critical applications, available with DPDT or dual lead/lag contacts (AFS-460-137, AFS-460-DSS), UL / CSA / FM approvals (DBL is CE / ISO 9001 / RoHS2 / WEEE only). Choose DBL for signaling-grade BAS interlocks and outdoor installations; choose AFS for motor switching, manual-reset safety sequences, or where UL listing is required.
What is the switching differential and can I adjust it?
The switching differential (also called "deadband") is the pressure DROP below the trip point that must occur before the switch resets. The factory default for all DBL switches is +/-15% of the trip point. For this SKU, the switching differential is field-adjustable across 0.08-0.16 inWC via an internal screw - but ACI does NOT recommend adjusting it. A smaller switching differential can cause failures and changes the switch behavior outside the datasheet specification (especially if the mounting position changes or higher electrical loads are used). Leave the factory default unless you have a specific reason to change it.
Which port do I connect to - P1 or P2?
P1 (+) is high pressure, located on the lower part of the housing. P2 (-) is low pressure, on the upper part. Connection options: Positive pressure only: connect to P1; leave P2 open to atmosphere. Negative pressure only: connect to P2; leave P1 open. Differential: connect the higher pressure to P1 and the lower to P2. On pressure increase, the SPDT contact transfers from 3-to-1 (NC) to 3-to-2 (NO); on pressure decrease, it transfers back. Use ACI's DBZ-06 duct-mount kit for the simplest in-duct pickup.
What's the correct mounting orientation?
Best practice: mount vertically with the pressure ports pointing downward. If horizontal mounting is required, deduct 0.08 inWC (20 Pa) from the desired set point to compensate for the gravity offset. Never mount with the set-point knob facing downward - this causes incorrect switch performance. If the set point is at the bottom of the range, do NOT use horizontal mounting at all - the offset will push the trip point below the achievable minimum. Surface-mount via four screws through the integral bracket; do not over-tighten, as deforming the plastic housing can cause air leakage.
How do I wire the SPDT contact?
The SPDT (Form 1C) micro switch has three spade-terminal connections: 3 (Common), 2 (Normally Open), and 1 (Normally Closed). With no pressure applied, contact 3 is connected to 1 (NC). On pressure increase past the set point, the contact transfers to 3-to-2 (NO). For "prove flow" logic (circuit closes when pressure rises - typical for fan-status verification), wire to 3 and 2. For "prove no flow" logic (circuit opens when pressure rises - typical for filter-clog alarm), wire to 3 and 1. Use 16-26 AWG twisted-pair or shielded cable; spade terminals accept maximum 16 AWG (1.5 mm²). Run through the 1/2" NPT conduit knockout.
What accessories do I need for installation?
Recommended: DBZ-06 duct-mount kit - includes two metal right-angle pitot tubes, two grommets, and 6.5 ft (2 m) of tubing - the DBL-specific in-duct pickup accessory. Alternatively, generic ACI pitots (PT 3", PT 5.2", PT 7.5", PT 9.7" foam-gasket; SPT-3.5", SPT-8.0" aluminum static; VPT, VPT-8" aluminum velocity) can be paired with longer tubing kits (A/10' TUBE, A/20' TUBE, A/50' TUBE, A/100' TUBE). Pickup ports for wall/room pressure taps: A/SP-PUP stainless, A/R-PUP beige, A/R2-PUP white, A/O-PUP-H / A/O-PUP-V outdoor weatherproof. Wire: 16-26 AWG twisted-pair or shielded cable, 1/2" conduit fitting if used.
What can I switch with the DBL?
The DBL is rated 250 VAC maximum, 1.5A resistive (0.4A inductive) - not enough to switch motors, solenoids, or contactors directly. The DBL is designed to signal a BAS controller, alarm panel, or interposing relay, which then switches the larger load. Typical loads: BAS digital input (a few mA), 24 VAC pilot relay coil (well under 1.5A), panel indicator light (low resistive load). If you need to switch a 1/4-hp fan motor or a high-current solenoid directly, use the AFS-460 (15A at 277 VAC, manual reset) or the AFS-222 / AFS-262 (15A non-inductive at 277 VAC, automatic reset).
What media is compatible with this switch?
Air and other non-combustible, non-aggressive gases: clean ambient air, nitrogen, argon, dry CO2. The silicone diaphragm is NOT compatible with: liquids of any kind, refrigerants, corrosive gases (chlorine, ammonia, hydrogen sulfide, acid fumes), combustible mixtures, or media that will degrade silicone. Maximum operating pressure is 40 inWC (10 kPa); exceeding this can damage the diaphragm and cause permanent calibration drift or complete failure.
What's the warranty?
2-Year ACI Limited Warranty - covers manufacturing defects in materials and workmanship under normal use. The 1,000,000-cycle life rating means a DBL cycled 100 times per day would mechanically last about 27 years (warranty is 2 years from purchase). Manufactured in Middleton, Wisconsin, USA. ZOT Supply is an authorized ACI distributor; warranty claims are processed directly with ACI. Full warranty terms are in the front of ACI's Sensors & Transmitters catalog at workaci.com.
- Series:
- DBL
- Pressure Range:
- 0.2-2 inWC
- Range Class:
- Low
- Contact Style:
- SPDT
- Reset Style:
- Automatic
- Sample Line Fitting:
- Push-on (3/16 in ID plastic/poly)
- Maximum Pressure:
- 40 inWC (10 kPa)
- Approvals:
- CE, ISO 9001, RoHS2, WEEE
- Mounting:
- Vertical (port down preferred)
- Made in USA:
- Yes
