The ACI SPT-3.5" is an aluminum static pressure (aspiration) probe with a 4.0 in (101.6 mm) insertion length — used to monitor static pressure in HVAC ducts or equipment. The probe tip opens parallel to the air stream (distinguishing it from velocity / impact probes which open into the air stream), measuring duct static pressure without sensing dynamic pressure components.
Mount the probe perpendicular to the duct (90 deg +/-3 deg) approximately 5 to 8 duct diameters downstream from elbows, obstructions, or large changes in duct area to reduce turbulence that would corrupt the reading. The 1.50 in flange has four 3/16 in (4.76 mm) mounting holes for screw or rivet fastening to the duct; a 3/8 in hole in the duct accepts the 1/4 in (6.35 mm) probe body. The probe ships with 6 barbed tubing connection points on the flange — accepts 1/8 in through 1/4 in ID flexible plastic tubing — for flexible installation routing.
Static pressure monitoring in HVAC ducts where a short insertion length is appropriate — small ducts, equipment with limited probe clearance, or applications where the duct static reading does not require deep mid-duct sampling. Filter status, fan operation, and general duct static monitoring in non-critical applications.
Key Features
The probe tip opens parallel to the air stream — measuring static pressure only, without sensing velocity / dynamic pressure components. The distinguishing characteristic vs. velocity (VPT) probes, which mount with the tip into the air stream.
Solid aluminum probe body with 4.0 in (101.6 mm) insertion length and 1/4 in (6.35 mm) outside diameter. Aluminum gives long service life, resistance to typical duct conditions, and the rigidity needed for mid-duct mounting.
The 1.50 in (38.1 mm) flange has six 45 deg barbed tubing fittings (only one used per installation; others provide routing flexibility). Accepts 1/8 in through 1/4 in ID flexible plastic tubing — compatible with ACI medical-grade tubing kits and any standard pneumatic tubing of equivalent quality.
Storage and operating temperature -40 to 185 deg F (-40 to 85 deg C). Suitable for duct installations in conditioned and non-conditioned spaces, including makeup air ducts and outdoor air handling units.
Mounting flange 1.50 in (38.1 mm) with four 3/16 in (4.76 mm) mounting holes for #8 x 3/4 in TEK screws (not included). Total weight 0.022 lb (10 g) — minimal impact on duct integrity. RoHS2, WEEE, and REACH compliant.
Technical Specifications
| Specification | Value |
|---|---|
| SKU | SPT-3.5" |
| Series | Static Pitot Tube |
| Probe Type | Static / Aspiration |
| Tubing Connection | 45 deg barbed type (6 places), accepts 1/8 in through 1/4 in ID flexible plastic tubing |
| Probe Insertion Length | 4.0 in (101.6 mm) |
| Sensing Points | 1 (single point) |
| Tube Mounting Direction | Tip opens parallel to the air stream |
| Static Tube Mounting Angle | Perpendicular to the duct (90 deg +/-3 deg) |
| Mounting Flange Diameter | 1.50 in (38.1 mm) |
| Measurement Probe Hole Size | 1/4 in (6.35 mm) |
| Mounting Holes Diameter | 3/16 in (4.76 mm) |
| Material | Aluminum |
| Storage & Operating Temperature | -40 to 185 deg F (-40 to 85 deg C) |
| Operating Humidity | 0 to 90% RH non-condensing |
| Weight | 0.022 lb (10 g) |
| Agency Approvals | RoHS2, WEEE, REACH |
| Warranty | 5-year ACI Limited Warranty |
What’s In the Box
- ACI SPT-3.5" Aluminum Static Pitot Tube (4.0 in insertion length)
- Installation instructions (also available below as PDF)
Recommended Companion Products
The SPT-3.5" requires 1/8 to 1/4 in ID flexible plastic tubing to connect to a differential pressure transmitter. ACI medical-grade tubing kits in four lengths:
Other ACI aluminum static / duct-static pitot tubes in the same family:
Documentation
Frequently Asked Questions
The SPT-3.5" is an aluminum static pressure (aspiration) probe — a duct-mounted pickup with a 4.0 in insertion length. It measures static pressure in the duct (the pressure component independent of air velocity), feeding the signal through 1/8 to 1/4 in ID tubing to a differential pressure transmitter or pressure switch. Standard applications: filter status monitoring, fan operation verification, and duct static pressure trending.
The probe tip orientation: static probes like the SPT mount with the tip parallel to the air stream (the tip opening points sideways relative to the flow); velocity / impact probes like the ACI VPT mount with the tip facing into the air stream (the tip opening points upstream into the flow). Static probes measure pressure only; velocity probes measure total pressure (static + dynamic), which is then used to compute air velocity / flow rate. Use the static probe for filter-status, fan-operation, or duct static monitoring; use the velocity probe for true air flow measurement.
Pick the 3.5 in (SPT-3.5") when the duct or equipment opening is small, when interior clearance is limited (compact air handlers, packaged equipment, small round duct), or when the application doesn't require deep mid-duct sampling. For larger main ducts where the probe tip should reach closer to the centerline for representative static sampling, the 8 in (SPT-8.0") variant is the better choice.
Approximately 5 to 8 duct diameters downstream from elbows, obstructions, transitions, or other large changes in duct area — this places the probe where turbulence has settled out and the static pressure reading is most representative. Drill a 3/8 in hole in the duct, insert the probe through the hole until the flange is tight to the duct, drill pilot holes for the four #8 x 3/4 in TEK mounting screws (not included), and fasten the flange tightly to eliminate air leaks. Mount perpendicular to the duct with the probe tip parallel to the air stream.
The probe accepts 1/8 in through 1/4 in ID flexible plastic tubing. For long runs, 1/4 in tubing minimizes pressure drop in the line. ACI offers FDA-compliant medical-grade flexible PVC tubing kits in 10 ft, 20 ft, 50 ft, and 100 ft lengths. Keep the run as short as practical to minimize response time; avoid sharp bends and low points where condensation can collect.
Any low-DP differential pressure transmitter that accepts 1/8 to 1/4 in flexible tubing on the high- or low-pressure ports — including ACI's own DLP and MLP2 series, BAPI ZPM zone pressure multi-sensors, Dwyer Series 682 industrial pressure transmitters (when configured for duct static monitoring), Dwyer RSM / RSME / RSMC room status monitors, and most other manufacturers' low-DP air pressure transmitters. The probe is a passive pneumatic accessory; brand compatibility is determined by the tubing fitting size, not by electronic interfacing.
