Series-1251-1253-1254Configuration

Supported Applications

The Dwyer Series 1251, 1253, and 1254 are heavy-duty welded chamber level switches designed for liquid level control in industrial applications. These hermetically sealed assemblies operate via a magnetic plunger mechanism attached to a stainless steel float within the chamber. Documented application areas include refineries, chemical plants, power stations, and water treatment systems.

Operating Conditions & Performance

The series is engineered for liquids with a minimum specific gravity of 0.40. Process temperature ratings extend up to 500°F (260°C), while ambient operating temperatures are rated to 212°F (100°C). Pressure capabilities vary by model and flange class, ranging from 275 psi at 100°F down to 150 psi at 500°F for Series 1253/1254 with 150# flanges, up to a maximum of 1250 psig (86 bar) across the temperature range from 100°F to 500°F for specific configurations. Repeatability is specified as ±1/4" (6.4 mm). The switches are available with UL approval.

Pressure Ratings by Model and Flange Class

• Series 1251: Carbon steel body with combination 1" NPT/socket weld hubs; rated to 1250 psig (86 bar) at 100°F (38°C) through 500°F (260°C).
• Series 1253: Side/bottom process connections with flanges. Ratings include: 275 psi/150 psi for 1" 150#; 720 psi/625 psi for 1" 300#; and 1250 psi/1250 psi for 1" 600# flanges.
• Series 1254: Side/side process connections with flanges. Ratings include: 275 PSI/150 psi for 1" 150#; 720 psi/625 psi for 1" 300#; and 1250 psig (86 bar)/1250 psig (86 bar) for 1" 600# flanges.

Configuration Options

The series offers configurable enclosures, circuit arrangements, and chamber materials to meet diverse installation requirements. Enclosure options include General Purpose (G), Weather Resistant (WT or W), Explosion-proof (E), and Explosion-proof Vapor-proof (EV). Housing materials vary by enclosure type: painted steel and aluminum for G; painted steel, aluminum, and neoprene for WT; aluminum for E; and aluminum with neoprene for EV.

Enclosure Ratings

• G: General purpose, NEMA-1.
• WT/W: Weather proof, NEMA-3R, 4, 4X.
• E/EV: Explosion-proof or explosion-proof vapor-proof. Rated for Class I Groups B, C, D and Class II Groups E, F, G (NEMA-7, 9).

Circuit Configurations

The switches support single-stage and two-stage operations with either mercury contacts or snap-action contacts. Electrical ratings vary by switch type:

• Mercury Contacts (Chart A): Available in SP-ST, SP-DT, DP-ST, and DP-DT configurations. AC ratings include 10A at 120V, 5A at 240V, and 3A at 440V†. DC ratings are up to 10A at 125V.
• Snap Action Contacts (Chart B): Includes standard snap switches (-78XX) with AC ratings of 12A/5A/3† and high-capacity DC options (-98XX). Hermetically sealed variants are available as -HM suffixes. High capacity DC models require heat fins if process temperature exceeds 350°F (177°C), with a maximum limit of 450°F (232°C).

Materials and Options

Standard wetted materials include carbon steel chambers with trim options in 303SS, 304SS, 316SS, or 430SS. Option C216 provides a 316SS chamber and trim with a 430SS armature, breather, and drain for E type enclosures, recommended for high humidity or outdoor service.

Key Product Differences

The primary distinction between the three series lies in their process connection geometry. Series 1251 utilizes combination 1" NPT/socket weld hubs with side/bottom connections and a carbon steel body. Series 1253 features flanged process connections (side/bottom) available in 150#, 300#, or 600# classes. Series 1254 is configured for side/side flanged process connections, also offered in 150#, 300#, and 600# ratings.

Model numbering follows the format: Type-Enclosure-Circuits-Welded Chamber Construction-Options. For example, a weatherproof unit with snap action and 1250 psig rating is designated as 1251-WT-7810-C1-40. Weights vary by configuration: Series 1251 weighs approximately 40 lb (18 kg), Series 1253 at 50 lb (22.7 kg), and Series 1254 at 57 lb (25.8 kg).