Analysis of the root causes: Jamming of the pneumatic cylinder Festo DNG-200-100PPV-A in the conditions of Ukrainian production

1. Introduction

At one of the heavy machine-building enterprises in Ukraine, the forcing press stopped due to the failure of the executive mechanism — the Festo DNG-200-100PPV-A pneumatic cylinder. The equipment worked in a three-shift mode with about 14,000 hours of operation after the last routine maintenance. The MTBF (mean time to failure) declared by the manufacturer for this series is 20,000 hours, subject to compliance with compressed air quality standards. The emergency shutdown resulted in a loss of line productivity for 4 hours and significant costs for unscheduled repairs. The chief engineer of UNITEC-D GmbH conducts a detailed analysis of the reasons for the failure to prevent such incidents.

2. Overview of the component

Double-acting pneumatic cylinder Festo DNG-200-100PPV-A (piston diameter 200 mm, stroke 100 mm) meets the standards ISO 15552. It is designed to work in harsh industrial environments.

• Working pressure: from 0.6 to 10 bar (nominal — 6 bar).
• Operating temperature range: from -20°C to +80°C.
• Piston speed: up to 1 m/s.
• Damping type: adjustable pneumatic damping in end positions (PPV).

This unit is located in close proximity to a source of moisture and dust, which requires increased attention to the air conditioning system according to the requirements of ISO 8573-1.

3. Evidence of refusal

During the initial inspection at the place of operation, the following symptoms were recorded:

• Complete jamming of the rod in the middle position of the stroke.
• 350% increase in cylinder activation time before stopping (according to the PLC controller).
• The presence of an oily emulsion with impurities of metal powder in the outlet nozzle of the distributor.
• Elevated temperature regime of the cylinder cover (up to +55°C compared to the norm of +30...°C), which indicates internal friction.

State and international standards used in the analysis: ISO 8573-1 (compressed air quality), ISO 19973 (reliability assessment of pneumatic components), DSTU EN ISO 4414 (safety of hydraulic and pneumatic systems).

4. Study of root causes

The Ishikawa diagram method and the "5 Whys" analysis were used to determine the chain of events that led to the accident.

1. Why did the rod stop? — The piston jammed in the sleeve due to the destruction of the seals and the accumulation of wear products.
2. Why did the seals collapse? — The material lost its elasticity due to chemical exposure and lack of proper lubrication.
3. Why was there no lubrication? — Lubrication was washed away by condensate, which formed due to the high dew point of compressed air.
4. Why did condensation form? — The refrigerating dehumidifier on the main line operated with a deviation from the norms (the dew point temperature was +12°C instead of the standard +3°C).
5. Why didn't the dehumidifier alarm go off? - The humidity sensor was blocked by a layer of dust and grease due to lack of calibration for 2 years.

5. Determined root causes

6. Corrective and preventive actions

Immediate Fix:

• Dismantling of the Festo DNG-200-100PPV-A cylinder, complete disassembly, damage to the sleeve and piston.
• Replacement of the seal repair kit (polyurethane cuffs according to DIN ISO 5597).
• Cleaning the inner surface of the sleeve from wear products and applying a special silicone lubricant for pneumatics.

Long-term prevention (Long-term Prevention):

• Repair and calibration of the central dryer of compressed air (achieving a dew point not higher than +3°C).
• Installation of an additional fine-cleaning coalescing filter (class 1 according to ISO 8573-1) directly in front of the consumer.
• Implementation of automatic blowing of condensate on receivers.

7. Quick diagnostic checklist for technicians

Use this checklist on your tablet during your equipment walkthrough every shift:

• [ ] Check the readings of the manometer at the inlet to the pneumatic group (working pressure 6 ± 0.5 bar).
• [ ] Inspect the filter-regulator bowl for moisture and grease.
• [ ] Test the operation of the automatic condensate drain valve.
• [ ] Evaluate the noise level when moving the rod (absence of jerks and jams).
• [ ] Check the condition of the protective corrugation and the rod mudguard for cracks.
• [ ] Measure the temperature of the cylinder covers with a pyrometer (limit up to +45°C).
• [ ] Check the tightness of the connections using a soapy solution or an ultrasonic tester.
• [ ] Check dew point parameters on main dehumidifier (target value +3°C).

8. Strategy to prevent refusals

In order to minimize the risks of downtime at the enterprises of the Ukrainian industry, it is necessary to follow a clear regulation:

• Service intervals: Carrying out a complete technical inspection of pneumatic cylinders every 8,000 hours or once a year.
• Condition monitoring: Use of vibroacoustic sensors for early detection of burrs on the piston surface.
• Air quality: Daily monitoring of air conditioning systems in accordance with DSTU regulations ISO 8573.

9. Conclusion

The seizure of the Festo DNG-200-100PPV-A pneumatic cylinder was caused by a combination of moisture and lubricant washout due to wear of the compressed air dryer. Timely detection of symptoms and modernization of the air conditioning system will avoid emergency shutdowns. Original repair kits, air cylinders and air conditioning components are available to order through the UNITEC-D E-Catalog.

10. Links

• ISO 8573-1:2010 "Compressed air. Part 1. Pollution and classes of purity".
• DSTU EN ISO 4414:2015 "Hydraulics and pneumatics. General rules and safety of systems and their components".
• ISO 15552:2018 "Pneumocylinders with collapsible housing, nominal pressure up to 10 bar".
• Technical documentation of the manufacturer Festo for the DNG series.
• Handbook on failure tolerance analysis of industrial equipment (MRO Handbook, UNITEC-D GmbH, 2023).