The function of Stuffing Box:

The piston rod stuffing box is a component that prevents the mixing of the crankcase atmosphere with the scavenge space. It is bolted to the diaphragm plate, and the piston rod passes through this stuffing box. The stuffing box casing, often split vertically for ease of maintenance, contains multiple sets of scraper rings and sealing rings, each composed of three to four segments held together by garter springs.

Sealing Ring:

The primary function of the sealing ring is to seal the boundary between the scavenge space and the crankcase. It prevents the mixing of the two atmospheres, thereby maintaining the separation of the crankcase atmosphere (which is pressurized) from the scavenge space beneath the piston. This ensures that no contaminants from the scavenge space enter the crankcase and no gases from the crankcase mix with the scavenge air.

The sealing ring typically consists of a spring and a ring, where the spring applies constant pressure to keep the sealing ring in contact with the piston rod, ensuring a tight seal.

Scraper Ring:

The function of the scraper ring is to scrape oil off the piston rod during both the upward and downward strokes. As the piston rod moves through the stuffing box, the scraper ring ensures that excess oil is removed and prevents it from contaminating the crankcase oil. This helps maintain the cleanliness of the piston rod and prevents the mixing of crankcase oil with the scavenge air. Any oil removed by the scraper ring is directed into the stuffing box drain tank.

The scraper ring consists of lamellae, a spring, and a ring. The lamellae are designed to scrape the oil off the piston rod, the spring ensures proper tension and contact with the rod, and the ring holds the components together.

Difference Between Sealing Ring and Scraper Ring

• The sealing ring prevents the mixing of the crankcase atmosphere and the scavenge space, ensuring proper sealing between these two areas, whereas the scraper ring scrapes off excess oil from the piston rod, preventing contamination of the crankcase oil and keeping the piston rod clean.

• The sealing ring typically consists of a spring and ring, whereas the scraper ring has additional components like lamellae for scraping action.

• The scraper rings are positioned above and below the sealing ring, and their primary function is to remove excess oil, while the sealing ring is positioned between the scraper rings to maintain a seal.

• Measure and record the wear of each ring (both sealing and scraper). Compare the values against the manufacturer’s recommended wear-down limits. Replace rings if the wear exceeds permissible limits.
• Inspect the scraper rings and lamellae for signs of scratching, burning, or breakage. Any damaged rings must be replaced.
• Examine the sealing rings for cracks or deformation, which can compromise their sealing efficiency.
• Check the garter springs for breakage or elongation. If elongation exceeds the manufacturer's limits, replace the springs to ensure proper tension.
• Take care to distinguish between the upper and lower scraper rings as they are not interchangeable. Install each ring in the correct position and orientation as per the manufacturer’s instructions.
• Ensure all rings and springs are properly seated within their grooves to avoid operational issues or premature wear.
• Inspect and clean the drainage pathways for oil and scavenge residue to prevent blockages.