Alutal Measure & Trust

Series 3 ASME B31.1, ASME B31.3 and NACE external cage level switch

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The product

ASME B31.1 Construction

Series 3 ASME B31.1 float-actuated level switches are designed, built, and certified to the requirements of ASME B31.1 power piping codes. They are ideal for critical alarm set points in clean liquid applications.

ASME B31.3 Construction

Series 3 ASME B31.3 float and displacer-actuated level switches are designed, built, and certified to the requirements of ASME B31.3 power piping code requirements. They are ideal for critical alarm set points in clean liquid applications.

NACE Construction

Series 3 NACE float and displacer-actuated level switches are designed, built and certified to meet NACE MRO175 and MRO103 requirements. They are ideal for alarm and control set points in sour liquid applications.

All welding is performed by qualified welders and per procedures required by the ASME Boiler Pressure Vessel Code Sec. IX. Carbon steel pressure boundary parts are post weld stress relieved. All welds and heat-affected zones are hardness tested to ensure compliance with NACE maximum hardness requirements.

External cage switches technology

A permanent magnet is attached to a pivoted switch actuator. As the float/displacer rises following the liquid level, it raises the attraction sleeve into the field of the magnet, which then snaps against the non-magnetic enclosing tube, actuating the switch. The enclosing tube provides a static pressure boundary between the switch mechanism and the process. On a falling level, the float/displacer deactivates the switch.


  • Models built to ASME B31.1, ASME B31.3, and NACE MR0175/MR0103 construction
  • 14-inch (356 mm) side/side process connections available as standard
  • Service pressures up to 2240 psig (154.4 bar)
  • Process temperatures up to +1000 °F (+538 °C)
  • Specific gravity ratings as low as 0.33
  • Choice of TYPE 4X/7/9, Group B, C & D or EEx d IIC T6 housings
  • Agency approvals include FM, CSA, ATEX and SAA
  • Choice of single or multiple switches for single or staged applications
  • Special materials of construction available upon request
  • Available with special coatings including Epoxy, Carbo Zinc® 11 Primer and Carboline Top Coat, Dimetcote® and Amercoat


  • Threaded, socket weld or flanged process connections
  • Custom actuation levels
  • Custom installation dimensions
  • Optional high or low temperature insulation available
  • Choice of switch mechanism: ? Dry contact ? Hermetically sealed ? Pneumatic
  • Choice of switch mechanism enclosure: ? TYPE 4X/7/9 Class I, Div. 1, Groups B, C & D, polymer coated aluminum ? NEMA 1, carbon steel for pneumatics
  • Choice of tank connection: ? 1″, 1½” or 2″ NPT ? 1″, 1½” or 2″ flanged side/side ? 1″, 1½” or 2″ flanged side/bottom ? 1″, 1½” or 2″ socket welds
  • Vent and drain connections

Operating principle

The buoyancy force of a process liquid on the float or displacer causes it to move with the liquid level change. This movement positions an attraction sleeve in the field of the switch magnet, pulling the magnet toward the sleeve and actuating the switch


EAC (GOST) Ex d, Ex ia
IEC Ex d, Ex ia
Inmetro Ex d
Korea Ex d
SIL SIL 2 (1oo1)

Other approvals are available. Consult factory for more details.

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