LevelAc Switches and Control - SL-400 Series

LevelAc Switches and Control - SL-400 Series

SL-400 Series

Level Ac Displacer Type Level Switches are designed for top mounting and are particularly suited for the level control of liquids under conditions of turbulence or agitation. Their operating principle produces relatively wide switching differentials.

Changes in operating differentials and actuating levels may be made in the field by repositioning the displacers along the stainless steel cable. Porcelain displacers are standard on the SL-400 series. Standard cable length is 10 ft.

LevelAc sl-400 series switch


  • Mounting Flanges: See Model Numbering, Table-5
  • Sizes: 2 1/2" 3", 4" standard
  • Materials: Steel - 150 lb. and 300 lb. ANSI Cast Iron - 125 lb. and 250 lb. ANSI Stainless Steel - 150 lb. ANSI
    Note: Other flange sizes, ratings and materials available on order.
  • Displacers: Porcelain standard. Stainless Steel available. See Model Numbering, Table 6.
  • Cable: 316 Stainless Steel
  • Clamps: 316 Stainless Steel standard.
  • Magnetlc Armature: 430-F corrosion resistant steel.
  • Support Spring: Stainless Steel
  • Support Spring Housing: Stainless Steel
  • Spring Retainer: Stainless Steel
  • Snap Ring: Stainless Steel
  • Specific Gravity Ranges: Mercury Switches -- 0.6 to 1.8 Snap Switches -- 0.8 to 1.8
  • Temperatures: 300° F (Ambient around displacers and around switch mounting)
    NOTE: Since specific gravity and temperature affect calibration, these values must be specified on order.
  • Pressure: See Model Numbering, Table 4
  • Differential Adjustable Minimum: 4" Maximum: to cable length, 10 ft. standard.

Switch Housing:

  • Explosion-proof: Heavy cast aluminurn base and cover. With drain; NEMA 7A, B, C, D; 8C, D; 9E, F, G; 10; 12; 13.
  • Vapor-proof: Similar to Explosion-proof except with "O" ring seal at base and no drain, NEMA 5; 7C, D; 9E, F, G; 10; 12; 13.

NOTE - Explosion-proof and Vapor-proof housings are U/L and CSA Approved as float-operated motor control unit for use in hazardous locations.

Switch Stations:

  • Number: One or two.
  • Mercury Type: Equipped with one or two SPDT mercury switches.
  • Snap Type: Equipped with one or two SPDT electrical snap switches or one pneumatic switch.

Principle of Operation

Model SL-400 LevelAc level switches use 'heavier-than-liquid" displacers which sink below the surface of the liquid under control. Spring suspension balances the normal displacer weight and as the liquid level rises around the displacer, it is buoyed up by a force equal to the weight of the liquid displaced. The apparent weight loss allows the spring to move the internal armature into the externally mounted switch's magnetic field to produce switch operation.

Mercury 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".

Switch Characteristics:

  • Mercury Switch: Hermetically sealed. SPDT mercury capsule switches are standard. Anti-vibration mercury capsules are optional/


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 - -

*Anti-vibration switch rating

  • 4 amp @ 120 VAC; 3amp @ 240 VAC
  • 4 amp @ 120 VDC; 2amp @ 240 VDC
  • Internal Wiring: 20 gauge copper (105 strands of no.40 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.
  • Snap Switches Characteristics: Non-mercury SPDT snap-acting type. Fully enclosed in high-strength plastic.
    • 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