Pneumatic Actuator Clamping Units
Cylinders with integrated clamps are needed on a machine when maintaining actuator position is essential to human and work-piece safety. A clamp keeps the actuator rod in a stationary vertical position and prevents it from retracting. Compressed air maintains the spring-loaded clamp in the open position. Should there be a leak or an emergency evacuation of air, the spring snaps the clamp closed and holds the rod or guide rail in place until air pressure is restored.
Pneumatic Actuator Brakes
Pneumatic brakes are designed to stop a moving actuator regardless of position—and not damage the rod or guide during an emergency stop. Brakes are more expensive than clamps, and they require third-party certification. Similar to clamps, air pressure maintains the brake in an open position. A spring snaps the brake closed when air is evacuated during an emergency stop or when air leaks out of the circuit.
A mechanical lock automatically engages a locking pin each time the cylinder reaches its end point. This effectively holds the rod or guide in position. Positive air pressure is required to raise the locking pin and permit the actuator to retract. Like clamps, mechanical locks are often applied in vertical holding applications. But mechanical locks are not used in areas where there is a high risk of injury because only the end position is controlled, not intermediate positions.
Position Feedback: Mechanical Flag and Linear Potentiometer
In some applications, keeping track of piston position at all times is vital for safe operation. A reliable safety technique is detecting piston position using a metal flag and inductive sensor. A linear potentiometer senses the flag position. A PLC can be programmed to shut down processes, remove pressure, and apply a brake or clamp if it indicates a fault position. The set-up can be used with rotary as well as linear actuators.
Self-Adjusting Air-Cushion Cylinders
Self-adjusting pneumatic cushions mount inside actuators and provide gentle damping near the end of stroke. They eliminate the need to manually adjust end-position cushioning. The cushion relies on specially engineered air channels to vent the cushioning air, letting the cushions adapt their characteristics should cylinder loads and speeds change.
Tamper-Proof Shut-Off Valves
Tamper-proof “Lock Out Tag Out” (LOTO) valves manually shut off and vent pneumatic systems. Once pressure has been evacuated, maintenance personnel insert a lock or hasp in the valve, making it impossible to restore pressure while the lock is in place. Depending on pneumatic configurations, there may be several tamper-proof valves per machine. These valves are OSHA-compliant.
On-Off Valves with Piston Sensing
Unlike manually operated tamper-proof valves, a PLC electronically controls solenoid-actuated on-off valves with piston-position sensing. These units sense piston position and confirm the valve is either on or off. Position sensing provides an extra margin of safety monitoring, and on-off valves can be integrated into a system to achieve a higher-category safety rating.
Emergency Quick Exhaust
Emergency quick-exhaust systems vent air from circuits at extremely high rates. When a penetrated light curtain or an open guard, gate, or door activates an emergency stop switch, these PLC controlled units exhaust air from the system at rates up to 9,000 liters/min—effectively removing pneumatic pressure. These units should also protect against unexpected startups and provide for safe pressure buildup.
Piloted Check Valves
A piloted check valve retains pressure in a cylinder and holds it in place when air pressure is turned off. It’s particularly useful in vertically mounted actuators where unprotected movements could damage the machine, part, or people. Piloted check valves are useful for both emergency situations and for safety during maintenance.
Tamper-Proof Flow Controls
Conventional flow-control valves let operators and maintenance personnel tinker with valve settings for on-the-fly adjustments to air flow, and that can change machine performance and cause unexpected safety problems. Special tamper-proof flow-control valves include a spring pin that protects against unauthorized resetting of flow rates.