When it comes to machine operations, safety is a must. Businesses that require their employees to work on or near hazardous energy must commit to implementing best safety practices, which include detailed safety risk assessments. This is necessary when working with the safety standard DIN-EN-ISO 13849-1, which was put in place in 2012.
This standard provides safety requirements and guidance on principles for the design and integration of safety-related parts of control systems, regardless of the type of technology and energy used (electrical, hydraulic, pneumatic or mechanical) for all kinds of machinery.
Know and eliminate risks
Safety should begin before the machine is fully installed and operational. For example, avoid risk at the initial design stage by reducing power and avoiding interference in the danger zone. Installing safety and protection devices is critical as well. These can include fences, light grids or control devices, as well as a lockout/tagout interface.
To work within this standard, a risk assessment must be completed. This begins with determining what the scope of the machine is, including all the space needed for the machine’s intended applications. All risk sources must be identified for all operations throughout the machine’s lifecycle. A risk estimation is then made for each risk source.
According to the standard, the risk is estimated according to three factors—injury severity (S, severity), frequency you have exposure to the risk (F, frequency) and the possibility you have of avoiding or limiting the injury (P, possibility).
It also includes performance levels “a” to “e” that reflect the reliability of the product and categories “1” to “4” that reflect the reliability of the safety circuits. Performance level “a” and category “1” are considered the lowest in terms of safety, while performance level “e” and category “4” are the highest.
Stored energy can be a danger
In today’s heavily automated plants, machinery often runs 24/7 and requires regular maintenance checks to avoid unexpected line shutdowns. Before conducting one of these maintenance checks, machine operators should always disconnect the power supply—as well as the fluid power supply connections—to avoid accidents and injuries. But even this critical safety step may not be enough.
When machines are not in use, compressed air acts like stored energy in pneumatic systems. The release of hazardous energy, deliberate or otherwise, carries the very real risk of injury or even fatality. Before routine maintenance or during an emergency shutdown, this compressed air must be released to avoid equipment damage.
While there are numerous ways to implement safety practices, lockout/tagout remains one of the best when it comes to workplace safety. Safety standards require that each machine have a monitored dump valve to release compressed air in the form of stored energy and meet performance level “e” and category “4.”
The most commonly used safety trend in industrial facilities uses a lockout/tagout safety shutoff valve or a 3/2 solenoid operated or air piloted valve, combined with an air preparation (FRL) assembly. Although this system is used regularly throughout many industries, valve failure causes continued airflow to the machine, which can lead to costly damage and severe injury.
Inherently fail-safe valves
In addition to conforming to DIN-EN-ISO 13849-1, pneumatic safety valves should be inherently fail-safe without residual pressure. They should also offer dynamic self-monitoring, a double-valve control system and a poppet design with feedback signal ports. These valves should be designed for use with pneumatic clutch and brake systems and other 3-way safety functions.
Pneumatic press double valves, also known as dual air valves or press safety valves, are used to control the air actuated systems and machines, such as palletizing, wrapping, packaging, processing and power presses, which must always exhaust to a safe position. When used on spring-loaded clutches and brakes for mechanical power presses, they function as 3/2 air valves, normally in a closed position. In other words, when the solenoids are de-energized, the valve exhausts air from the clutch/brake unit (port 2 to 3) while preventing the inlet pressure from reaching the working port. When the solenoids are energized, air pressure is supplied to the clutch/brake unit, allowing the clutch to engage.
For example, Norgren’s Herion XSz dual redundant and dynamically monitored valves protect from injuries caused by the inadvertent release of stored energy. They are designed for self-checking in accordance with OSHA and ANSI. The advanced, double-valve design features a unique cross-flow pattern and air logic dynamic monitor. It is certified by independent testing organizations as a redundant and monitored dump valve for performance level “e” and category “4.”