Control Valves for Oil & Gas

A choke valve is a specific type of control valve designed for wellhead service — handling the extreme pressure drops (from reservoir pressure to separator pressure), sand-bearing fluids, and erosive conditions at the wellhead. Choke valves are designed to API 6A (wellhead equipment) and use highly erosion-resistant trim (tungsten carbide, ceramic). Standard control valves are designed to ISA-75 for process facilities (separators, compressor stations, refineries) and use SS, duplex, or alloy trim without the extreme erosion-resistance features of choke valves.

Cavitation occurs when a liquid control valve's pressure drops below the fluid's vapour pressure, causing vapour bubbles to form, then collapse violently as pressure recovers downstream. In oil & gas, cavitation is most common on separator level control valves handling pressurised liquid (high-pressure separator to low-pressure vessel). Prevention: use a multi-stage (cascade) trim that reduces pressure in steps, each below the vapitation threshold; select valve with high FL (liquid pressure recovery factor); or use a downstream back-pressure regulator to raise downstream pressure above vapour pressure.