Question

With reference to crankcase diaphragm glands:

(a) Explain why effectiveness deteriorates in service.

(b) Describe the procedure for renewal of parts so that efficiency is restored and rod scoring is avoided;

(c) Describe how effectiveness is restored if spares are unavailable;

(d) Explain the functions of the upper and lower sections.

Answer 1

Part (a)

Deterioration of Crankcase Diaphragm Gland Effectiveness:

The effectiveness of crankcase diaphragm glands diminishes over time due to wear and tear of the soft friction material comprising the gland segments. Initial installation leaves a 3-4 mm gap between segments. As wear progresses, these segments move closer, potentially butting against each other. Further wear then creates a clearance between the piston rod and the gland segments, permitting the passage of scavenge air, oil, sludge, and other contaminants. This leakage compromises the gland's sealing function.

Part (b)

Procedure for renewal of Stuffing box parts:

The diaphragm gland is typically overhauled simultaneously with the piston during piston withdrawal from the engine.

Mount the diaphragm housing on a table clamped to the piston rod.
Separate the housing into two sections by removing the clamping bolts.
Measure the clearances of the rings and check for wear.
Replace rings and garter springs if wear exceeds the manufacturer’s recommended limits.
Renew replaceable lamellae on the scraper rings if necessary.
Ensure proper installation of rings in the correct direction as per maker’s instructions.
Verify that the top and bottom scraper rings, which differ in design, are not interchanged.
Refit the cover and tighten the clamping bolts to secure the assembly.

Part (c)

Restoring Effectiveness When Spares are Unavailable:

A temporary fix involves carefully adjusting the butt clearances between the worn segments to restore the required sealing. This may involve trimming one segment, adhering strictly to manufacturer's instructions, to achieve the appropriate clearance and maintaining tension via the spring. This solution is temporary; replacement rings are essential as soon as they become available.

Part (d)

Function of upper and lower sections:

Lower Scraper Rings:

These rings scrape oil off the piston rod as it moves upward, preventing crankcase oil from contaminating the scavenge space. The oil is drained back into the crankcase through designated drain channels.

Upper Scraper Rings:

These rings remove oil and impurities from the piston rod during its downward stroke, preventing contamination of the crankcase oil. The scraped oil is directed to the scavenge space, where it is drained.

✓ Verified Model Answer (Text Solution)

Deterioration of Crankcase Diaphragm Gland Effectiveness:

Procedure for renewal of Stuffing box parts:

Restoring Effectiveness When Spares are Unavailable:

Function of upper and lower sections: