The Towa Seiden PRL-G7-40 Heavy-Duty Explosion-Proof Rotary Paddle Level Switch, manufactured by Towa Seiden Industrial Co., Ltd. (Japan), is the premier mechanical point level detection instrument designed for hazardous operational environments characterized by extreme mechanical stresses. The model represents the apex of structural protection within the PRL Series, combining Japanese industrial d2G4 flameproof certification (equivalent to international Ex d IIB T4 Gb standards) with an extra-large 40A heavy-duty protective tube sleeve shielding the drive mechanism.

Mechanical engineering benchmark of the PRL-G7-40:
- Compared to the 25A model (outer diameter Ø34 mm), the PRL-G7-40 upgrades the protective sleeve to a nominal 40A pipe size (outer diameter approx. Ø48.6 mm) fabricated from heavy-gauge SUS304 stainless steel. 
- This heavy-duty sleeve functions as an unyielding structural beam that completely absorbs violent lateral bending stresses, continuous avalanching forces, and falling impact momentum from tons of descending bulk material. The internal concentric rotating shaft is entirely decoupled from external physical loads, eliminating shaft deflection, seal damage, and bearing seizure when monitoring demanding media such as cement clinker, raw coal, gravel, and heavy mineral ores.

Regarding electrical safety, the PRL-G7-40 is certified to Japanese industrial flameproof rating d2G4 (Ex d IIB T4 Gb). The terminal enclosure housing the drive motor and microswitch assembly is cast from high-pressure aluminum alloy (ADC12) featuring precision-machined flameproof joint paths. This containment architecture safely absorbs and quenches internal gas ignition fronts without allowing sparks or thermal flame propagation into external combustible atmospheres, ensuring full compliance across Zone 1 and Zone 2 areas in petrochemical refineries, chemical processing plants, and solvent storage facilities.

The operational mechanism utilizes an electromechanical torque-reaction principle with integrated motor overload shut-off: an internal synchronous motor continuously turns the shaft and paddle assembly at approximately 1 RPM. When rising bulk solids impede paddle rotation, the resulting reactive torque rotates the suspended motor assembly, actuating a microswitch to trip the SPDT output contacts (250V AC, 5A) for alarm or feeder interlocking while immediately de-energizing the drive motor. This prevents motor coil overheating and burnout even during prolonged paddle burial under massive bulk heaps. 

Equipped with an industrial standard JIS 5K65A mounting flange and sealed to an IP65 ingress protection rating, the Towa Seiden PRL-G7-40 provides unmatched mechanical endurance exceeding a decade of maintenance-free service in the most abrasive and volatile plant environments.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Complete Part Number: Towa Seiden PRL-G7-40
• Product Classification: Heavy-Duty Explosion-Proof Protective Tube Rotary Paddle Level Switch
• Hazardous Area Certification: d2G4 (Japanese industrial flameproof standard, equivalent to Ex d IIB T4 Gb)
• Mechanical Protective Construction: Extra-large 40A heavy-duty protective tube sleeve (Pipe OD approx. Ø48.6 mm) resisting extreme lateral bending and impact loads
• Operating Principle: Electromechanical torque-reaction with automatic motor cut-off
• Supply Voltage Ratings: 100V AC, 110V AC, 200V AC, 220V AC (50/60 Hz) or optional wide-range 120-250V AC / 24V DC
• Power Consumption: Approximately 2.5 W to 3.5 W
• Paddle Rotational Speed: Approximately 1.0 RPM (at 50 Hz) / 1.2 RPM (at 60 Hz)
• Electrical Output Contact: 1 SPDT microswitch (Single-Pole Double-Throw)
• Contact Current Rating: 250V AC, 5A (Resistive load)
• Detectable Bulk Density: From 0.2 g/cm³ or greater (Specifically optimized for coarse solids, clinker, coal, gravel, and heavy ores)
• Process Mounting Connection: Standard Flange JIS 5K65A (Outer diameter 155 mm, 4 bolt holes on 130 mm pitch circle)
• Standard Immersion / Tube Length (L): 250 mm, 300 mm, 500 mm (Custom engineered lengths up to 1000 mm available)
• Standard Paddle Configuration: W-1 broad-vane paddle (80 x 80 mm) or folding paddle in SUS304
• Wetted Materials:
  - Shaft, Heavy-Duty Protective Tube (40A), and Paddle: Stainless Steel SUS304 (AISI 304) or optional SUS316
  - Shaft Sealing: High-performance abrasion-resistant mechanical packing seal / oil seal
• Terminal Housing Material: Heavy-duty aluminum diecast (ADC12) with flameproof structural integrity
• Process Vessel Operating Temperature: -10°C to +70°C (High-temperature options up to 150°C)
• Ambient Enclosure Operating Temperature: -10°C to +55°C
• Maximum Operating Pressure: Up to 196 kPa (approx. 2.0 bar / atmospheric pressure)
• Ingress Protection Rating: IP65 (per IEC/EN 60529 standard)
• Net Product Weight: Approximately 5.8 kg to 9.0 kg (depending on heavy-duty protective tube length)