Series-391-393-394Configuration

Supported Applications

The Dwyer Series 391, 393, and 394 are side-mounted, chamber-sealed liquid level controls designed for heavy-duty industrial applications. These single-stage, non-adjustable switches operate via a magnetic plunger and float mechanism to monitor compatible liquids in process vessels.

Documented use cases include refinery service environments where the series provides weatherproof protection against harsh conditions. The design supports high-pressure and high-temperature liquid level control tasks requiring gravity return action for long life without springs.

Operating Conditions & Performance

The Series 391, 393, and 394 are rated for process temperatures up to 600°F (315.6°C) with an ambient operating temperature of 212°F (100°C). Pressure ratings reach 800 psig (55 bar) at 100°F (37.7°C), reducing to 650 psig (45 bar) at 600°F (315.6°C); higher pressure ratings are available.

Switch operation is defined by specific liquid level changes based on the fluid's Specific Gravity (Sp.Gr.). For a Sp.Gr. of 1.0, dimension A measures 4-3/8" (111mm) and B measures 1" (25.4 mm). At a Sp.Gr. of 0.80, dimension A is 4-11/16" (191 mm) and B is 1-3/16" (12.3 mm).

Temperature limitations for specific switch types require heat fins or high temperature switches when process temperatures exceed the following thresholds: above 500°F (260°C) with mercury switches, above 400°F (204°C) with snap switches, and above 350°F (176.7°C) with hermetically sealed snap switches.

Key Performance Specifications

• Pressure Rating: 800 psig (55 bar) at 100°F (37.7°C); 650 psig (45 bar) at 600°F (315.6°C)
• Process Temperature: Up to 600°F (315.6°C)
• Ambient Temperature: 212°F (100°C)
• Enclosure Rating: NEMA 4X standard; optional general purpose or explosion-proof enclosures
• Weight: 10 lb (4.5 kg)

Configuration Options

The series offers configurable options across switch types, materials of construction, and process connections to accommodate diverse installation requirements.

Switch Types & Electrical Output

• SPDT Mercury: Model 391-WT-4810-C1-80
• SPDT Snap Switch: Model 391-WT-7810-C1-80 (hermetically sealed snap switch option available)
• SPDT Hermetically Sealed Snap: Model 391-WT-7810HM-C1-80
• Electrical Connection: Screw terminal with a standard 3/4" female NPT conduit connection (rotatable 360°)

Materials & Construction

• Body Material: Carbon steel welded chamber; stainless steel bodies available for specific controls where dimensions A, B, and C may vary.
• Float and Trim Materials: 303 SS, 304 SS, 316 SS, and 430 SS
• Housing Options: Weatherproof (standard), General Purpose ('G'), or Explosion-Proof ('E')

Process Connections

• Standard Connection: 1" female NPT
• Optional Connections: 1" socket weld hub or flange connections

Key Product Differences

The Series 391, 393, and 394 differ primarily by switch mechanism type (mercury vs. snap vs. hermetically sealed) and enclosure rating (weatherproof NEMA 4X standard versus optional general purpose or explosion-proof). Model numbers follow the format 391-WT--C1-80, where the model segment identifies the specific switch configuration.

Differences in physical dimensions occur based on fluid Specific Gravity; controls designed for lower Sp.Gr. fluids (e.g., 0.80) exhibit larger dimension A and B values compared to those calibrated for Sp.Gr. 1.0. Additionally, stainless steel body variants may present dimensional variations relative to the standard carbon steel construction.

UL LISTED certification applies to the series; however, UL listing is not applicable on HM (mercury) switch configurations.