ACI AFS-460 : Differential Pressure Switch (Metal), 0.4-12 inWC, SPST-NC Contact, Manual Reset, Compression Fitting, 2-Year Warranty, Made in USA

What is the AFS-460 used for?

The AFS-460 is a general-purpose differential air pressure switch used in HVAC and Energy Management applications for monitoring filter blockage, proof of flow, prove excessive or insufficient flow, alarms and control. The snap-acting contact closes (or opens) when the differential pressure across the sensing diaphragm exceeds the 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 how the sample lines are connected.

What is the set point range and how do I adjust it?

The set point range is 0.4-12 inWC, adjustable in the field via the on-board adjustment screw. Procedure: turn the adjustment screw counterclockwise until motion stops, then turn 4 complete turns clockwise to engage the calibration spring; the next 10 turns are the active calibration range. Each full turn represents approximately 1.16 inWC per full turn (10 calibration turns total). Use a digital manometer or other measuring device to confirm the actual set point during calibration - the turn-count is a starting reference, not a precision calibration.

What's the difference between manual and automatic reset?

Manual reset (this SKU): after the switch trips, it stays in the tripped state until the operator presses the reset button on the enclosure - required for safety-critical applications where the system must NOT auto-recover after a fault (fan-failure shutdowns, freeze-protection lockouts, filter-replacement alarms). Automatic reset (the AFS-222 and AFS-262 variants): the switch resets itself when pressure returns to the normal range - appropriate for continuous monitoring applications where transient excursions are expected and don't require operator intervention.

Why does the switch need to be mounted vertically?

The diaphragm must be in a vertical plane to achieve the lowest specified operating set point. Mounting horizontal puts gravity load on the diaphragm that biases the trip point and prevents the switch from reaching its lowest rated operate range. Also avoid mounting with the sample-line connections pointing upward - condensate will accumulate in the tubing and affect both response time and trip-point accuracy. Surface-mount via the two 3/16" diameter holes in the integral mounting bracket; the holes are 3-7/8" apart center-to-center.

What sample-line tubing should I use?

This switch accepts 1/4" OD rigid or semi-rigid metallic tubing via the integral compression fittings (ferrule and nut). Tubing length guidelines: for sample lines up to 10 feet, 1/4" OD tubing is acceptable; for lines up to 20 feet, use 1/4" ID tubing; for runs from 20-60 feet, step up to 1/2" ID tubing to avoid degrading the response time. ACI offers medical-grade tubing kits in various lengths: A/10' TUBE, A/20' TUBE, A/50' TUBE, A/100' TUBE. Locate the sampling probe a minimum of 1.5 duct diameters downstream from the air source, as close to the center of the airstream as practical.

Which inlet do I connect to - high or low?

Positive pressure only: connect the sample line to inlet H (high); leave inlet L (low) open to atmosphere. Negative pressure only: connect to inlet L; leave inlet H open to atmosphere. Two negative samples: higher negative sample to inlet L, lower negative sample to inlet H. Two positive samples: higher positive sample to inlet H, lower positive sample to inlet L. One positive and one negative sample: positive to inlet H, negative to inlet L. The pressure DIFFERENCE between H and L is what drives the diaphragm.

What accessories do I need for installation?

Required: sample-line tubing (specified above), 14-22 AWG wire appropriate for the contact load, and 1/2" conduit if your install requires conduit routing. Application-dependent: sampling pitot tubes for in-duct pressure pickup (PT 3", PT 5.2", PT 7.5", PT 9.7" foam-gasket; SPT-3.5", SPT-8.0" aluminum static flat tip; VPT, VPT-8" aluminum velocity pointed tip), or 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). Keep sample-line runs as short as practical for fastest response time.

What media is this switch compatible with?

Air. The diaphragm is NOT compatible with: liquids of any kind, refrigerants, corrosive gases (chlorine, ammonia, hydrogen sulfide, acid fumes), or media that will degrade silicone elastomers. Maximum overpressure tolerance is 0.5 psi (3.45 kPa); exceeding this will damage the diaphragm and can cause permanent set-point drift or complete failure. For liquid-pressure switching, see Belimo's wet/wet differential pressure switches in the Liquid Pressure subcategory.

What agency approvals does this switch carry?

This switch is UL, CSA, CE approved. The UL listing covers the mechanical endurance test of the snap-acting switch mechanism and the electrical isolation between the contact circuit and the diaphragm-sensing portion of the device. For mission-critical safety applications (life-safety smoke control, fire-suppression interlocks), verify the specific agency listings required by your local AHJ - this switch is a general-purpose proving switch, not a UL864 life-safety device.

What's the warranty?

2-Year ACI Limited Warranty - covers manufacturing defects in materials and workmanship under normal use. The full warranty terms are in the front of ACI's Sensors & Transmitters catalog at workaci.com. Manufactured in Middleton, Wisconsin, USA. ZOT Supply is an authorized ACI distributor; warranty claims are processed directly with ACI.