In bulk material handling industries such as mining, ports, power generation, metallurgy and cement, belt conveyors are typically characterized by long conveying distances, high loads and continuous operation. When an emergency occurs on site — such as belt misalignment and tearing, material blockage, equipment failure, or personnel entering a hazardous area — whether the power supply can be cut off and the machine stopped quickly at any position along the conveyor line is directly related to equipment safety and the safety of human life.
As the most essential on-site emergency shutdown protection device for belt conveyors, the XLLS-X-F bi-directional pull cord switch (Bi-directional Pull Cord Switch) allows inspection and operating personnel to pull the steel wire rope at any position along the conveyor line to achieve instantaneous shutdown. This article systematically analyzes the working principle, innovative structural features, technical parameter matrix, on-site installation specifications, and wiring and commissioning procedures of the XLLS-X-F.
1. Working Principle and Triggering Mechanism of the Bi-Directional Pull Cord Switch
The bi-directional pull cord switch is connected to the switch swing arm by means of plastic-coated steel wire ropes laid along both sides of the conveyor.
When an emergency occurs along the conveyor line, on-site personnel can pull the wire rope connected to the swing arm in any direction:
- Mechanical transmission process: the pulling force overcomes the resistance of the internal spring and drives the swing arm on the outside of the switch to deflect.
- Action angle control: when the deflection angle of the swing arm reaches 20°~30° (action range), the internal cam triggers two independent micro switches (limit switches), instantly switching the state of the output contacts.
- Signal output: the switch issues a shutdown command to the control system (PLC/DCS) and cuts off the power supply circuit of the main drive motor, thereby achieving an emergency stop.
- Locking and reset mechanism: the XLLS-X-F adopts a Type II manual reset structure. After being triggered, the swing arm automatically locks in the alarm position (the limit angle of the swing arm can reach 75°); even if the pulling force on the rope is released, the switch remains in the shutdown state. Only after the on-site fault has been eliminated and the reset button or reset wrench on the housing is pressed by hand can the equipment return to normal operation.
2. Structural Features and Protection Innovations of the XLLS-X-F Product
Compared with traditional pull cord switches, the XLLS-X-F has undergone multiple technical upgrades in protection rating, anti-interference capability and on-site installation convenience:
- High-strength die-cast aluminum alloy housing: the housing is precision die-cast from high-quality aluminum alloy, featuring high mechanical strength and outstanding resistance to heavy impact and strong vibration; the housing surface is electrostatically spray-coated under high pressure for acid and alkali resistance and corrosion protection.
- Rainproof and dustproof protective cover (newly added): a dedicated external protective cover effectively blocks splashes, snow accumulation, falling material and external falling objects from striking the swing arm, greatly reducing the false alarm rate caused by material impact.
- Direct locking structure of the swing arm: the wire rope fastening method has been upgraded. A dedicated fastening bolt is designed at the end of the swing arm, so the wire rope can pass directly through the swing arm and be locked with the bolt without complex rope clip winding, greatly improving installation efficiency.
- Integrated junction box design: an independent terminal block is built inside and the wiring cavity provides ample space, making it extremely convenient for on-site construction personnel to lead in cables and complete the wiring directly.
- High protection and weather resistance: the housing protection rating reaches IP67 and is equipped with high-quality sealing gaskets, allowing long-term stable operation under extreme ambient temperatures of -40℃~+50℃ and in harsh outdoor working conditions with high dust and high humidity.
3. Core Technical Parameter Comparison Table
To facilitate engineering selection and control system design, the key parameters of the XLLS-X-F bi-directional pull cord switch are shown in the table below:
| Parameter | Specification |
|---|---|
| Model | XLLS-X-F (X series bi-directional pull cord switch with protective cover) |
| Output mode and quantity | 2 × SPDT (two sets of independent single-pole double-throw contacts) |
| Contact rating | AC 380V 5A / DC 24V 5A |
| Action force | 70 ~ 100 N |
| Adjustment range | 20° ~ 30° |
| Limit angle | 75° |
| Reset mode | Manual reset (Manual Reset) |
| Electrical life | > 200,000 operations |
| Protection level | IP67 |
| Ambient temperature | -40℃ ~ +50℃ |
| Relative humidity / atmospheric pressure | 0 ~ 95% / 80 kPa ~ 110 kPa |
| Applicable cable outer diameter | 6 ~ 10 mm |
4. Standardized On-Site Installation and Pull Cord Layout Specifications
Correct installation and wire rope tensioning are the key to ensuring that the pull cord switch acts sensitively and does not raise false alarms.
Safety precautions (WARNING)
- Live working is strictly prohibited: before installation, wiring or maintenance, the on-site main power supply must be disconnected and lockout/tagout must be applied.
- Non-explosion-proof product statement: this product is an ordinary industrial high-protection device and must never be used directly in flammable and explosive gas environments.
Materials and accessories to be prepared
- XLLS-X-F bi-directional pull cord switch body
- Dedicated mounting bracket (optional)
- Plastic-coated steel wire rope (optional; moisture-proof, acid and alkali resistant, flame retardant)
- Wire rope support rings (optional)
- M10×35 fasteners and external protective cover
Standard installation steps
- Mounting bracket and switch fixing:
- Fix the mounting bracket onto the frames on both sides of the belt conveyor by welding or bolts.
- Install the XLLS-X-F firmly on the bracket with M10 fasteners.
- Specifications for the installation spacing of switches:
- Bi-directional pull cord switches should be installed on both sides along the conveyor line, and the installation distance between two switches should preferably be 25~30 meters.
- For conveyors with a large slope or a complex environment, the installation spacing of the switches should be appropriately shortened.
- Running the wire rope and installing the support rings:
- Pass one end of the plastic-coated wire rope through the hole in the swing arm and lock it firmly and directly with the hexagon bolt of the swing arm.
- On the premise of ensuring normal operation of the switch, tension the wire rope as much as possible to reduce the sagging arc caused by the self-weight of the wire rope.
- Support ring arrangement: in order to eliminate the effect of the self-weight of the wire rope on the pulling force of the switch swing arm, a support ring must be welded or fixed on the frame every 3 meters to support the wire rope.
- Installing the protective cover:
- Place the transparent/metal protective cover over the switch and secure it to the switch body with the top fastening bolts, ensuring that the swing arm can freely deflect 75° inside the protective cover cavity.
5. Electrical Wiring Principle and Control System Integration
The internal junction box of the XLLS-X-F contains two sets of SPDT switch terminal blocks (marked and ).
Terminal wiring definitions
- : common terminal (Common).
- : normally open contact (Normally Open). Open during normal conveyor operation, closed when the pull cord alarm is triggered.
- : normally closed contact (Normally Closed). Closed during normal conveyor operation, open when the pull cord alarm is triggered.
Recommendations for system interlock integration
- Dual-circuit protection (hard interlock + PLC):
- Connect the first set of normally closed contacts () in series into the hardware control circuit of the main drive motor contactor. Once the pull cord is pulled, the contactor coil is cut off directly to achieve a hard shutdown.
- Connect the second set of normally open contacts () to the DI input module of the on-site PLC/DCS, so as to send the "pull cord emergency shutdown" alarm signal and positioning information to the central control room.
6. Routine Inspection, Maintenance and Common Troubleshooting
In order to ensure that the pull cord switch acts with 100% reliability in an emergency, a comprehensive inspection system should be established:
- Routine inspection requirements:
- Periodically clean dust from the switch housing and the protective cover to prevent excessive accumulated material from hindering the rotation of the swing arm.
- Check whether the plastic-coated wire rope is damaged, has broken wires or is loose; if fasteners or the wire rope are found to be seriously corroded, they should be replaced in time.
- Periodic action test:
- Every month, during conveyor shutdown and maintenance, manually pull the on-site wire rope to verify whether the swing arm acts sensitively and whether the PLC alarm signal and the reset function work normally.
- Troubleshooting guide:
- The switch does not act when the wire rope is pulled: check whether the wire rope is too loose so that the travel does not reach 20°; check whether the swing arm fixing bolt is loose or has fallen off.
- The switch is still in the alarm state after manual reset: check whether the reset spring of the internal micro switch is stuck, or whether there is a short circuit at the terminal block.