Introduction

When steam temperature control has to be accurate across changing loads, Copes-Vulcan’s VO Variable Orifice Desuperheater is the benchmark. It combines exceptional turndown (typically up to ~100:1 with Cascade trim), ±5 °F (±2.5 °C) control accuracy, and low cooling-water head (only ~5 psi above steam)—all in a compact, line-mounted design that usually needs no liners or long downstream runs. KV Controls specifies and supports VO units across power, petrochemical, pulp & paper and more.

How the VO works

Inside the VO, a free-floating plug lifts with steam flow to create a variable orifice. That action produces a near-constant pressure drop at the seat. Cooling water—metered by a control valve—is introduced uniformly around the seat into a low-pressure, high-turbulence zone. The turbulence finely atomizes the water for rapid mixing, so the steam reaches setpoint quickly and consistently.

Five reasons plants choose VO

Big, controllable turndown – With a Copes-Vulcan control valve using Cascade trim, the VO typically achieves ~100:1 rangeability while maintaining stable control.

Tight temperature accuracy – Controls to ±5 °F (±2.5 °C); approach as close as 10 °F (5 °C) above saturation.

Low water pressure requirement – Cooling water only needs ~5 psi (0.35 bar) above steam pressure at the VO inlet.

Compact installation – Because desuperheating largely happens inside the body, the temperature sensor can be just 4–6 m downstream; liners and long straight runs are usually unnecessary.

Backed by Celeros FT – The Copes-Vulcan range is designed for mission-critical service across power and process industries.

Models & selection

VO-II – Standard design per ANSI B16.5; sizes 3–20 in (80–500 mm); materials include WCB and WC6; pressure classes ASME 150, 300, 600, 900.
VO-76 – Same performance as VO-II but offered when Class >900, larger sizes, or custom end connections are required. Available as cast or fabricated housings with numerous reducer/flange options—ratings up to Class 1500 shown.

Typical applications

Boiler/turbine bypass cooling and PRDS trains in power, plus steam conditioning across oil & gas, chemical, and pulp & paper.

Installation essentials (quick checklist)

Mount vertically with upward steam flow.
If a bend is immediately downstream, use a long-radius elbow.
Place the RTD/temperature sensor ~4–6 m from the outlet.
Fit a non-return valve in the spray-water line and use a fast-response temperature controller.

Sizing—what we need from you

KV Controls will size the VO precisely. Share: steam flow(s), pressure, superheat temperature, desired outlet temperature, available water pressure & temperature, and line size/schedule.

VO vs. other Copes-Vulcan options

For high-temperature duties that don’t need VO’s full capability, the Multiple Nozzle Spray Desuperheater (MNSD-V/U) can bridge the gap; for severe service valves, see SD Severe Duty. Our team will steer you to the right solution.