WIKA A2G-40 Differential Pressure Switch for HVAC Air

WIKA A2G-40 differential pressure switch for ventilation and air-conditioning

The WIKA A2G-40 is a differential pressure switch for dry, clean, non-aggressive gases, usually air. Its job is to monitor filters, ventilators and blowers in ventilation ducts, air-conditioning units and clean room installations, and to monitor overpressure in clean rooms and laboratories. It is offered in six pressure range increments from 20 … 200 Pa to 500 … 4,500 Pa, in a plastic case with side-mounted hose nozzles and an M16 cable gland. Seven Star LLC supplies the A2G-40 in Oman and the GCC as an independent supplier in Muscat, and this page explains the ranges and electrical limits so that the RFQ can name the right range and application.

How the A2G-40 switches

Two hoses connect the switch to the two pressure points, for example the upstream and downstream side of a filter. A silicone diaphragm inside the case moves with the difference between the two pressures and operates a contact when the difference reaches the set point. The set point is adjusted within the chosen pressure range, and the contact returns when the difference falls by the switch differential (hysteresis) given in the data sheet. The device is in the Δp function: it monitors a pressure difference rather than a single pressure.

As a filter monitor the switch gives a signal when the pressure drop across a dirty filter exceeds the set value, and as a fan monitor it signals the loss of pressure rise when a belt breaks or a motor trips. In clean rooms it can indicate loss of overpressure. Because there are six ranges, an installation can pick the increment that suits the clean filter drop and the alarm drop.

Technical specifications of the A2G-40

Switching power of the A2G-40

The contact rating depends on the range. For the lowest range (20 … 200 Pa) the data sheet gives 0.1 A resistive at AC 125 V, AC 250 V and DC 30 V. For all other ranges the resistive rating is 3 A at AC 125 V, AC 250 V and DC 30 V, and 2 A on inductive loads (cos φ about 0.6 to 0.7). At DC 125 V the resistive rating is 0.4 A and the inductive rating 0.05 A on those ranges. The lowest range therefore suits signalling to a PLC input or a relay coil, while the others can drive small contactors or alarm horns directly. Always confirm the load type, because a rating given for a resistive load does not apply to inductive devices.

Where the A2G-40 fits and related WIKA models

If a continuous signal is needed instead of an alarm contact, the A2G-55 Eco differential pressure transmitter measures the same low air pressures with a 0 … 10 V or 4 … 20 mA output. Both models use hoses of similar size and the same wall-mounting style, so a filter monitoring design can use the transmitter for trending and the switch for a hard-wired alarm. Where liquids or higher pressures are involved, WIKA gauges such as the 732.51 differential pressure gauge or switch-type instruments in other families apply.

Selection and ordering checklist for the A2G-40

• Range increment, chosen so that the alarm value lies inside it and above the lowest limit with margin.
• Contact load: resistive or inductive, voltage and current, especially for the 20 … 200 Pa range.
• Hose size 4 … 6 mm and the length to the duct.
• Units shown on the scale: Pa, kPa, inWC, mmWC or mbar.
• Medium: air or clean, dry, non-aggressive gas only.
• Ambient and medium temperature within the limits.
• Approvals such as EAC, if required.

Installation and commissioning of the A2G-40

Mount on a wall (the data sheet lists wall mounting) and connect the plus hose to the higher-pressure point and the minus hose to the lower-pressure point. Keep hoses short and free of liquid pockets, and take pressure from duct connectors facing away from the flow. Set the switch point as described in the operating instructions, then verify it with a hand pump and manometer, since the data sheet allows an upper limit tolerance of ±15 %. Fit the cable through the M16 gland and close the cover to maintain the IP54 rating. Avoid mounting the switch where condensate can run into it; the housing is not for wet spaces.

Typical applications in Oman and the GCC

Gulf air conditioning plants run with high dust and sand loading, so the pressure drop across filters can rise quickly. The A2G-40 gives an alarm for filter replacement in air handling units of hospitals, hotels, malls, offices and industrial buildings, and it signals a fan failure in ducts and cooling-tower air systems. It is also used in clean rooms and laboratories to monitor overpressure, within the limit of medium temperature of -20 to +60 °C.

A2G-40 ranges compared

Information to send with an RFQ

• A2G-40 with range in Pa
• Contact load and voltage
• Scale unit
• Quantity and delivery site

Documents and quotation

The WIKA data sheet for the A2G-40 is attached on this page.

Send the range, unit and quantity and Seven Star LLC will confirm availability and a quotation.