Hydac EDS 3146-3-02.5-000-F1 Absolute Pressure Switch

Absolute pressure switching for vacuum and low-pressure systems

The Hydac EDS 3146-3-02.5-000-F1 (HYDAC part number 908635) is the absolute-pressure version of the EDS 3000 range. Absolute means the zero point is a perfect vacuum, so atmospheric weather changes do not shift the switching point. The range is 0 to 2.5 bar absolute, which covers the vacuum side up to moderate overpressure.

The device has a ceramic measuring cell with thick-layer strain gauge, a rotatable four-digit LED display, one PNP transistor output and a switchable analogue output of 4 to 20 mA or 0 to 10 V.

Technical specifications

Typical absolute-pressure tasks

Examples are vacuum pump control, suction line monitoring on refrigeration or air-conditioning plant, and low-pressure checks in the food and pharmaceutical industries, which HYDAC names for the series. The fine increments of 0.005 bar allow accurate setting near atmospheric pressure. For a gauge-pressure reading choose the EDS 3300, and for an absolute transmitter without switching see the HDA 4100.

Selection notes

With an 8 bar overload limit and a 12 bar burst pressure the switch must not be used in lines that can see higher pressure even briefly. Confirm the medium is compatible with the FKM seal; an EPDM seal option exists for water and refrigerants. Pin and menu details are in the EDS 3100 datasheet, which is the USA edition (psia and NPT); the bar and G1/4 values here are taken from the catalogue entry for this part number.

Before ordering, state whether the application measures vacuum, absolute pressure or gauge pressure, and the minimum and maximum process pressure, so the correct range and overload margin can be confirmed. Where condensate or oil mist can reach the ceramic element, mount the port upward or use a trap. Mount the switch with the port facing downward only if condensate cannot collect against the ceramic element, and avoid fast pressure shocks during start-up of a vacuum system.

The display and keys let you set switching points on site, so commissioning does not need a separate configuration tool. Note the 0 to 2.5 bar absolute range, which is intended for vacuum and low-pressure circuits and is not suited to high-pressure hydraulics.

Installation on vacuum and low-pressure lines

Choose a tapping point on a straight, accessible section of the line where the pressure represents what the process needs to control, for example close to the vacuum pump suction or at the vessel being evacuated. Fit the G1/4 A connection with the FKM seal seated correctly and tighten to the 20 N·m stated in the specification; over-tightening a small port gains nothing and may damage the seal face. On vacuum service, a leaking joint draws air into the system rather than releasing fluid, so a poor seal shows up as an unexpectedly high absolute reading rather than as a visible drip.

Rotate the LED display to face the operator before final tightening of the cable, and route the M12 cable with a loop so that moisture runs off before reaching the connector. Keep the cable away from motor power wiring and frequency converter outputs, particularly when the analogue signal is used.

Commissioning the switch and analogue output

First compare the displayed value with a reference instrument at a known condition; with the line open to air, an absolute device should read the local atmospheric pressure, not zero. This simple check confirms that the absolute version has been fitted and helps catch confusion with gauge-pressure devices. Then set the switching point, the hysteresis or window values and the output mode using the keys, choosing values within the ranges listed in the table.

Select 4 to 20 mA or 0 to 10 V to match the PLC input, and check the scaling in the control system against the 0 to 2.5 bar absolute range. Run the process through its normal cycle and confirm that the PNP output changes at the intended pressures and that the analogue value tracks the reference gauge.

Heat, dust and humidity in Oman sites

Refrigeration plants, food factories and packaging lines in the Gulf often run equipment in warm rooms with humid air near the coast. The operating and fluid temperature limits of -25 to +80 °C cover most of these locations, but the best accuracy is achieved inside the compensated range of -10 to +70 °C, so avoid mounting the switch directly on hot pump casings or in direct summer sun on rooftop units. Vacuum lines that pull warm humid air can collect condensate, which is a further reason to follow the mounting guidance above. Keep the M12 connector properly mated with its cable so the IP 67 protection is maintained in dusty environments, and wipe sand and dust off the display window during routine rounds so readings stay easy to check.

Maintenance and periodic checks

During planned maintenance, compare the reading with a calibrated reference, look for oil or condensate deposits at the process connection, and confirm that the switching point and output configuration still match the documented values. If the reading has drifted or responds slowly, isolate the line, vent it safely and inspect the port before replacing the device with the same HYDAC part number 908635. Record every setting change in the equipment file so that the next technician knows which values were proven during commissioning.

Documents and quotation

The datasheet is attached. Please give the code, the medium and the quantity. See also our pressure instrumentation range.