The Towa Seiden PRL-F7 Explosion-Proof Flexible Wire Rope Rotary Paddle Level Switch, manufactured by Towa Seiden Industrial Co., Ltd. (Japan), is an industrial point level detection instrument engineered specifically for vertical top-mounting in deep storage silos where hostile explosion-hazardous conditions coexist with violent bulk material movements. The instrument combines Japanese industrial d2G4 flameproof certification (equivalent to international Ex d IIB T4 Gb standards) with a high-tensile flexible stainless steel wire rope suspension stem.

Key engineering hallmarks of the Towa Seiden PRL-F7:
1. Flexible Wire Rope Suspension Architecture: In tall storage silos exceeding 2 to 4 meters in depth, rigid shaft extensions are vulnerable to severe lateral bending stresses and buckling caused by massive bulk subsidence and collapsing material cones. The PRL-F7 supersedes rigid shafts with a heavy-duty SUS304 stainless steel wire rope assembly coupled to a bottom weighting element and paddle. This flexible design allows the paddle to yield dynamically with bulk material flow without transmitting destructive bending moments to internal bearings or the motor housing, entirely eliminating shaft distortion.
2. Certified Flameproof Safety (Rating d2G4 / Ex d IIB T4): The terminal compartment housing the drive motor and microswitch assembly is cast from high-pressure aluminum alloy (ADC12) featuring precision-machined flame-arresting joints. Certified to withstand internal gas explosions without allowing flame or sparks to escape into surrounding atmospheres, it ensures full compliance across Zone 1 and Zone 2 areas in petrochemical refineries, chemical processing plants, and solvent storage facilities.
3. Heavy-Duty JIS 5K65A Flange Connection: Equipped with a standard JIS 5K65A mounting flange (155 mm outer diameter, 4 bolt holes), the unit fastens securely onto top nozzle openings, providing airtight containment against dust and volatile gas egress.

The operational mechanism of the Towa Seiden PRL-F7 utilizes an electromechanical torque-reaction principle with integrated motor overload protection: an internal synchronous motor turns the flexible shaft and paddle assembly continuously 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 deep bulk heaps.

All wetted components—including the wire rope, guide weight, and W-1 paddle (or folding paddle)—are constructed from high-grade SUS304 stainless steel. Enclosed in an IP65 diecast aluminum housing, the Towa Seiden PRL-F7 guarantees over a decade of dependable, maintenance-free performance in deep silo monitoring.

• Manufacturer: Towa Seiden Industrial Co., Ltd.
• Country of Origin: Japan
• Complete Part Number: Towa Seiden PRL-F7
• Product Classification: Explosion-Proof Flexible Wire Rope Rotary Paddle Level Switch
• Hazardous Area Certification: d2G4 (Japanese industrial flameproof standard, equivalent to Ex d IIB T4 Gb)
• Suspension Stem Construction: High-tensile SUS304 stainless steel flexible wire rope absorbing lateral avalanching forces
• 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 (Suitable for plastic pellets, cement, fly ash, coal, grains, and chemical powders)
• Process Mounting Connection: Standard Flange JIS 5K65A (Outer diameter 155 mm, 4 bolt holes on 130 mm pitch circle)
• Standard Flexible Rope Length (L): 500 mm to 4000 mm (Custom engineered to silo depth specifications)
• Standard Paddle Configuration: W-1 broad-vane paddle (80 x 80 mm) or folding paddle in SUS304
• Wetted Materials:
  - Flexible Rope, Bottom Weight, 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 5.2 kg to 8.5 kg (depending on flexible rope length and flange options)