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Spool lap configuration—the dimensional relationship between spool lands and valve ports—determines whether a valve has continuous flow (underlap), positive shut-off (overlap), or instantaneous switching (zero-lap), directly affecting cylinder control characteristics, positioning accuracy, and energy efficiency.

Proper valve seal material selection requires matching elastomer chemistry to operating conditions: NBR for general purpose applications, FKM (Viton®) for chemical resistance and high temperatures, and HNBR for enhanced performance across broader temperature and chemical ranges, with compatibility determined by polymer structure and additive packages.

Spool stiction results from molecular-level adhesion forces between valve surfaces and contamination deposits, primarily varnish-like compounds formed through oxidation, polymerization, and thermal degradation of lubricants and airborne contaminants, creating static friction forces that exceed normal actuating forces.

Anodizing and surface treatments dramatically extend valve spool life by creating protective barriers against wear, corrosion, and contamination, with hard anodizing providing up to 10x wear resistance improvement, while specialized coatings can reduce friction coefficients by 80% and eliminate galvanic corrosion in multi-metal systems.

Thread type selection and proper sealing methods are critical for pneumatic system reliability, with NPT threads using taper interference for sealing, BSP threads requiring gaskets or sealants, and G threads designed for O-ring sealing, each demanding specific installation techniques and compatible components for leak-free operation.