Heavy Parallel Pin of Atlas Copco RD18U in Iran

Iran's copper mining operations—Sarcheshmeh in Kerman Province, one of the world's largest porphyry copper deposits, and Sungun in East Azerbaijan—run Atlas Copco RD18U drifters on development and production drilling in hard granodiorite and metamorphic formations at 150–200 MPa UCS. The parallel pin in the RD18U's percussion module sets the precise angular alignment between the valve block and the percussion cylinder bore. Its fit—interference-press in the valve block face, slip-fit in the cylinder block—establishes the concentricity that keeps the reversing valve spool correctly positioned relative to the percussion bore. A worn or undersized parallel pin allows micro-rotation of the valve block relative to the cylinder under the percussion vibration loading, shifting the spool position and degrading the valve's switching precision.

In Iran, logistics constraints for original equipment parts have historically driven operations toward local fabrication of non-critical fasteners. The parallel pin is in the category that site-fabricated substitutes handle badly: the pin's diameter tolerance (typically h6 tolerance, ±0.006 mm) is tighter than standard commercial stock, and the surface finish (Ra 0.4 μm) is finer than turning centers produce without grinding. A pin made from commercial round bar on a local lathe may look identical but will have 3–5× the diametrical clearance and surface roughness of the original, producing the micro-rotation problem it was supposed to prevent.

Parallel Pin Specification

Iranian operations that have shifted to HOVOO-supplied original-specification RD18U parallel pins report elimination of the valve block micro-rotation symptoms that had been producing percussion irregularity on drifters serviced with locally fabricated pins. The pin cost is trivial; the precision it enables in the valve circuit is not. Full dimensional specifications and supply references at hovooseal.com.