Precise compressed air control in production: Analysis of the Festo GRLA-1/8-QS-8-RS-B and modern alternatives

1. Introduction: The importance of precise flow control for operational safety

In modern manufacturing processes, the precise control of pneumatic actuators is of critical importance for process stability, energy efficiency and operational safety. Inadequately controlled airflows result in jerky movements, increased wear and unnecessary energy consumption, which directly impact the overall operating efficiency (OEE) of the equipment. The Festo flow control valve GRLA-1/8-QS-8-RS-B (Festo item number 162966) has been a standard component for regulating the speed of pneumatic cylinders by throttling exhaust air for years. Since its discontinuation in 2023, maintenance teams have been faced with the challenge of implementing adequate replacement solutions that meet the high requirements for reliability and compliance. This technical analysis highlights the specifications of the original component and presents modern, standard-compliant alternatives to ensure continuous and optimized system performance.

2. Technical specifications of the Festo GRLA-1/8-QS-8-RS-B

The Festo GRLA-1/8-QS-8-RS-B is a robust one-way flow control valve designed for exhaust air throttling in pneumatic systems. Its design allows for sensitive adjustment of flow speed, which is essential for precise positioning and movement of cylinders.

Table 1: Detailed technical data of the Festo GRLA-1/8-QS-8-RS-B (item number 162966)

3. Functionality and physical principles

A one-way flow control valve like the Festo GRLA is based on the principle of throttling the medium in one flow direction while it flows almost unhindered in the opposite direction. This is achieved through the combination of an adjustable throttle point and an integrated check valve.

Throttling principle: The knurled screw positions a throttle cone in the air duct. By changing the cross section (A) of the throttle point, the flow resistance (R) is increased or reduced. According to the Bernoulli equation and the continuity equation, a reduction in the cross section leads to an increase in the flow velocity (v) and a decrease in the static pressure (p). The volume flow rate (Q) through a throttle can be expressed simply as proportional to the pressure difference (Δp) and inversely proportional to the flow resistance R:

Q ≈ Δp / R

The resistance R depends heavily on the geometry of the throttle gap. The precise adjustment of the exhaust air throttling is crucial to achieve the desired movement sequence of a cylinder, without uncontrolled accelerations or decelerations.

Check valve: In contrast to the throttling direction, the integrated check valve opens when flow is in the opposite direction. This enables a fast and unhindered flow of medium, for example for the quick return stroke of a cylinder. The check valve is designed as a spring-loaded element that opens when a low opening pressure (~0.05 bar) is reached and reveals the full cross section.

The material selection with reinforced PBT for the housing and brass for the adjusting screw ensures high chemical resistance and mechanical stability in accordance with DIN EN ISO 178 and DIN EN 12164.

4. Applications and areas of application in industry

One-way flow control valves are essential in a variety of industrial applications where control of linear and pivoting movements of pneumatic cylinders is required.

1. Automated assembly systems: For precise positioning of components and to avoid impact damage. Example: Slowly feeding a workpiece to a press or precisely placing a component on a mounting plate. The controlled movement reduces mechanical stress and increases the service life of the system according to VDI 2714.
2. Packaging machines: For controlling the lifting and lowering movements of grippers and rams in order to gently handle sensitive products. Abrupt lowering could result in product damage.
3. Robot technology: In pneumatically driven joints or grippers to adapt the dynamics of the movements to the process requirements and minimize vibrations.
4. Wood and metalworking: For feed regulation of tools or for clamping workpieces, where uniform and controlled movement is crucial for the processing quality.
5. Sorting and feeding systems: To regulate the ejection speed of objects to ensure a precise transition to the next process step.

5. Maintenance and life cycle consideration

The reliable function of flow control valves is crucial for the availability of pneumatic systems. The life cycle of the Festo GRLA-1/8-QS-8-RS-B and similar valves is significantly influenced by operating conditions and maintenance practices.

5.1. Common failure modes

• Throttle blockage: Particles in the compressed air system (even with ISO 8573-1:2010 [7:4:4] compliant air) can block the fine throttle opening, resulting in uncontrolled speeds.
• Seal wear: NBR and TPE-U(PU) seals can harden or leak over time due to aggressive media or high temperatures, which leads to loss of compressed air and inaccurate control.
• Damage to the adjustment screw: Mechanical stress or improper handling can damage the knurled screw or its thread, resulting in loss of adjustability.
• Check valve blockage: Debris can block the check valve, preventing free flow in the return direction and disrupting the system cycle.

5.2. Preventive maintenance

A proactive maintenance strategy according to VDI 3814 minimizes failures:

• Regular compressed air quality testing: Ensuring compressed air quality according to ISO 8573-1:2010 [7:4:4] through regular inspection of filters and dryers.
• Visual inspection: Inspection for mechanical damage, leaks or contamination.
• Functional test: Periodic checking of control accuracy and free return flow. Adjustment if necessary, taking cylinder movement into account.
• Replacement Intervals: Establishment of preventive replacement intervals for valves in critical applications, typically based on operating cycles or an estimated MTBF (Mean Time Between Failures) of 2,000 to 5,000 operating hours, depending on the application and load.

6. Comparison with modern alternatives

Given the discontinuation of the Festo GRLA-1/8-QS-8-RS-B, switching to modern alternatives is unavoidable. The Festo VFOE series offers a direct follow-up solution. There are also other market-leading products that offer adequate functionality.

Table 2: Technical comparison of one-way flow control valves (G1/8, hose Ø 8 mm)

7. Compliance with standards and safety aspects

The selection and operation of flow control valves must always comply with applicable standards and safety regulations, especially in the context of the Machinery Directive 2006/42/EC and the Pressure Equipment Directive 2014/68/EU.

• DIN EN ISO 4414:2010 (Pneumatics - General rules and safety requirements for fluid power systems and their components): This standard specifies the basic safety requirements for the design and operation of pneumatic systems. Correct installation and adjustment of the valves is essential.
• ISO 8573-1:2010 (Compressed air - Part 1: Impurities and purity classes): Ensuring compressed air quality prevents corrosion, clogging and premature wear of the valves. A classification of [7:4:4] is sufficient for the longevity of most pneumatic components.
• DIN EN ISO 6953-1 (Pneumatics – Flow control valves – Part 1: Identification and marking): This standard standardizes the marking of flow control valves, which facilitates correct selection and replacement.
• CE marking: All components sold in the EU must bear the CE marking, which confirms conformity with European directives.
• Functional safety: For safety-relevant applications (e.g. according to DIN EN ISO 13849-1), valves with specific safety functions or in redundant designs that go beyond standard flow control valves are often required. A risk assessment of the system is mandatory.

8. Conclusion

The Festo GRLA-1/8-QS-8-RS-B was a reliable component in pneumatic systems. Their discontinuation requires a strategic reassessment of component procurement. The Festo VFOE-LE-T-G18-Q8 offers a modern, compact and powerful alternative that meets both the technical requirements and offers the advantage of a wider availability range. The consideration of standards such as ISO 8573-1 and DIN EN ISO 4414 is essential for the safe and efficient operation of systems. Careful selection of components and a preventative maintenance strategy contribute significantly to minimizing downtime and maximizing system productivity.

For more information on flow control valves and other components for your pneumatic applications, visit the UNITEC-D E-Catalog.

9. References

1. Festo AG & Co. KG. (2024). Product data sheet VFOE-LE-T-G18-Q8 (item number 8068727).
2. SMC Corporation. (2024). Technical data of the AS2201F-01-08S series.
3. Bosch Rexroth AG. (2024). Product documentation for compressed air preparation and valves AS2.
4. DIN German Institute for Standardization (2010). DIN EN ISO 4414:2010 – Pneumatics – General rules and safety requirements for fluid power systems and their components. Beuth Verlag.
5. TÜV Rheinland. (2024). Test reports and certifications for pneumatic components.