Danfoss 017-140766 RT 121 Vacuum Pressure Switch

Danfoss 017-140766 RT 121 vacuum pressure switch, -1 to 0 bar

The Danfoss 017-140766 is an RT 121, the RT-series pressure switch for vacuum duty. Its regulation range is -1 to 0 bar g, so it switches on the suction side of vacuum pumps, ejectors and other sub-atmospheric systems, with an adjustable differential of 0.09 to 0.4 bar. The mechanical bellows element, SPDT snap contact and IP66 housing are the same construction as other RT switches, but the pressure side is rated for a modest 7 bar working pressure and 8 bar test pressure, which is the key difference from RT 116 and RT 5 units. Seven Star LLC supplies the 017-140766 in Oman and the GCC as an independent supplier in Muscat.

The manufacturer lists 017-521566 as an identical product on the Danfoss product page.

Reading the 017-140766 and RT 121 designation

017-140766 technical specifications

Using a vacuum switch correctly

A vacuum switch measures how far the pressure has dropped below atmospheric, so the set value is a negative gauge number. On the RT 121 the knob sets the lowest activating point and the differential disc raises the point at which it switches back. Because the range is narrow and the bellows has to respond to small pressure changes, the working pressure rating is deliberately low: connecting the RT 121 to a line that can see compressed air or surge pressure above 7 bar can damage the bellows. Where a system alternates between vacuum and pressure, check the maximum pressure it can see and, if necessary, protect the switch with a check valve or select a different type.

Typical settings include a vacuum pump start and stop band, a loss-of-suction alarm on a priming system, and a permissive in a package that must not start until suction conditions are established. The contact ratings allow the switch to drive small contactors and relays directly, with a 10 A 400 V AC-1 rating for resistive loads and 3 A 400 V for AC-15 inductive loads.

RT 121 compared with neighbouring RT low-range switches

The 017-140766 is at the vacuum end of the RT family. The RT 113 covers 0 to 0.3 bar, the RT 112 (017-140266) covers 0.1 to 1.1 bar, and the RT 110 (017-140966) covers 0.2 to 3 bar. All share the same housing, switch system and G 3/8 connection style, which simplifies spares and panel drawings. The RT 121 is the only one in this group whose scale lies fully below atmospheric pressure.

Selection and ordering checklist for RT 121

• Vacuum level at start, stop and alarm, expressed in bar g or mbar absolute and converted for the scale.
• Highest pressure the line can see in any mode, which must remain under 7 bar g.
• Differential between cut-in and cut-out that avoids short cycling of the pump.
• Medium compatibility with the bellows materials in the data sheet, and condensate or oil carry-over in the line.
• Electrical rating of the load and whether a gold-contact or manual-reset contact set is wanted.
• Class approvals needed; this code lists NKK and RINA but not BV, DNV or GL.

Installation and commissioning

Mount the unit with the pressure connection down where possible so that condensate drains away from the bellows, and use the spanner flats to counter the torque of the pressure line. The unit can be mounted in any position, but on plants with strong vibration the cable entry should face downwards. After wiring, check the actual switch points with a vacuum gauge, since the printed scale is only a guide and the narrow range makes small errors significant.

Applications of the 017-140766 in Oman and the GCC

Examples include vacuum packaging and degassing equipment at food and chemical plants, vacuum priming of large pumps at water and desalination stations, vacuum systems on turbine lube-oil reservoirs and condensate extraction lines at power plants. Warm, humid coastal air puts condensation on any cold surfaces, so keep cable glands tight and keep the switch drained.

Information to send with an RFQ for 017-140766

• Code 017-140766 and quantity.
• Vacuum set points and differential required.
• Medium, temperature and any pressure surge risk.
• Electrical load details.
• Required approvals.

Site conditions in Oman for the 017-140766

Field instruments in Oman are exposed to strong sun, high ambient temperature, wind-blown dust and, on coastal plants, salt in the air. When you specify the 017-140766, check the ambient and process temperature limits, the enclosure rating and the wetted and housing materials against the actual installation point, and consider sunshades for transmitters mounted in direct sunlight. Cable entries should be sealed with suitable glands so that dust and moisture cannot enter the housing.

Calibration and verification planning matters as much as selection. Record the range, configuration and tag data of each 017-140766 at commissioning, define a check interval that suits the criticality of the loop, and keep the certificates with the plant documentation so that audits and shutdown work can proceed without delay.

Documents and quotation

The Danfoss RT pressure switch data sheet, which includes the RT 121, is attached on this page.

Send the code 017-140766 and your vacuum settings and we will confirm availability and a quotation for Oman and the GCC.