LevelAc Switches and Control - SL-300 Series

LevelAc Switches and Control - SL-300 Series

Switching Differential - SL-300 Series

The SL-300 Series of side-mounted level switches are designed for installation on tanks where top access is not practical and where liquid turbulance and agitation is encountered. Sealed, welded float chambers are equipped with 1' NTP side and bottom process connections.

  • One Station: Adjustable ½" to 3½", Factory set at 11/2" unless otherwise specified.
  • Two Station: Adjustable, Adjusting nut spacing is factory set for minimum differential. Spacing between stations is set at 3" maximum, This center-to-center spacing is adjustable.
  • A - Station Differential (Lower)
  • B - Series Differential.
  • C - High - Low Differential
  • D - Station Differential(Upper)

Switch Stations

  • Number: One or two.
  • Mercury Type: Equipped with one or two SPDT mercury switches.

Switch Characteristics:

  • Mercury Switch: Hermetically sealed, SPDT mercury switches are standard.


Volts AC Amps* AC H.P. AC Pilot Duty DC Amps* DC H.P.
120 13 1/2 345 VA 10 1/2
240 6.5 1 345 VA 5 1/2
400 3 1 345 VA - -
  • Snap Switch: Non-mercury SPDT snap-acting type. Fully enclosed in high-strength plastic.
  • Rating:
    • 15 amps @ 120 or 240 VAC
    • 1/2 amp @ 120 VDC
    • 1/4 amp @ 240 VDC
    • Pilot duty --- 345 VA
  • Pneumatic Switch characteristics:
    A pneumatic valve with bail seating for tight closing and designed for mounting on a snap switching station. Snap-action of the switch station produces "on/off" or "closed/vent" operation. May be mounted to vent on high level or low level, Only one pneumatic switch per station may be installed.
  • Rating: 0 to 60 psi max.


PSI 9 15 20 30 40 50 >60
SCFM .63 .84 .99 1.29 1.58 1.86 2.16

Principle of Operation

LevelAc Switch SL-300 SeriesMercury Switching Station - A glass capsule containing the mercury and switch contacts is mounted on a pivoted arm. A magnetic armature moves up and down inside a non-magnetic sealing tube following movement of the float caused by changing liquid level in the float chamber. As the armature enters the field of the Alnico V magnet mounted on the opposite end of the pivoted arm, magnetic attraction causes the magnet to approach the sealing tube and tilt the mercury capsule to make or break an electrical circuit.

Snap Switching Stations: - An Alnico 8 magnet surrounds the sealing tube and concentrates powerful magnetic force in a small space. Movement of the armature into the magnetic field shunts attraction away from the external pole pieces which allows the pivoted actuator plate to "snap" the SPDT switch making the circuit "COM" to "NC" and breaking "COM" to "NO".

Interface Operation: To control the dividing line (interface) between two immiscible liquids of different specific gravities, the float is precisely loaded to sink in the lighter liquid above but be supported on the surface of the heavier liquid below. Float loading is based on the minimum specific gravity difference between the two liquids (highest sp. G of the lighter liquid and lowest sp. G. of the heavier liquid) at the operating temperature. For LevelAcs intended for interface service, complete information on specific gravities of both liquids must be furnished.

  • Internal Wiring: 20 gauge copper (105 strands of 40 gauge wire for extreme flexbility) insulated with silicone rubber.
  • Terminal Board: Bakelite barrier terminal strip. Terminal positions marked.
  • Switch Frame: Pivot arms and wiring shields are heavy gauge brass. For maximum corrosion resistance, frame may be zinc plated on special order.
  • Magnet: Alnico-V, stabilized
  • Pivots: Low friction "dog" type stainless steel pivot screws