Sizing a valve for capacity doesn't tell you whether it will destroy itself. A correctly-sized valve can still cavitate badly — this checks the pressure conditions that decide it.
Standard method — stated scope limits apply
Service Conditions
All pressures must be absolute and in the same unit (bar a, psia, kPa a — the analysis is unit-agnostic as long as you're consistent).
Pᵥ is at the flowing temperature, not ambient. Pᴄ is a fluid property (water ≈ 221 bar a).
Valve Data (from manufacturer)
Valve-specific. Roughly: globe ≈ 0.9 (low recovery), butterfly/ball ≈ 0.5–0.7 (high recovery, far more cavitation-prone). Use your actual valve's published figure.
Leave blank if you don't have them — the tool will say plainly what it can and can't conclude without them.
Enter service conditions and assess.
About This Calculation
Cavitation in a control valve happens when local pressure inside the valve drops below the fluid's vapor pressure at the vena contracta (the point of maximum velocity, minimum pressure), causing vapor bubbles to form — then, as pressure recovers downstream of the restriction, those bubbles collapse violently, causing the characteristic noise, vibration, and progressive erosion damage cavitation is known for. This check compares the valve's actual pressure drop against its cavitation-onset and choked-flow limits (both governed by the valve's own FL and sigma coefficients) to determine whether a given service condition is safely within limits, near onset, or genuinely damaging.
Frequently Asked Questions
What is the difference between cavitation and flashing?
Both start the same way — pressure dropping below vapor pressure inside the valve — but in flashing, downstream pressure never recovers above vapor pressure, so the vapor bubbles never collapse; they simply persist into the downstream piping. Cavitation specifically requires downstream pressure to recover enough for the bubbles to collapse violently, which is what causes cavitation’s characteristic damage that flashing (without collapse) does not.
Why does cavitation damage the valve body downstream of the restriction, not at the restriction itself?
Bubbles form at the point of lowest pressure (the vena contracta) but haven’t collapsed yet there — as the flow decelerates and pressure recovers downstream, that’s where the bubbles actually implode, and the resulting micro-jet impacts and pressure shock waves are what erode the valve body and downstream piping surfaces at that location.
What do FL and the sigma indices actually represent?
FL (liquid pressure recovery factor) describes how much pressure recovery a specific valve geometry produces downstream, which sets its choked-flow limit. The sigma indices (incipient, constant, damage) are valve-specific values from manufacturer testing marking the pressure-ratio thresholds at which cavitation first begins, becomes steady, and becomes damaging — they genuinely vary by valve trim design, not just size.
Can cavitation be avoided by simply choosing a bigger valve?
Not necessarily — a larger valve sized for the same flow operates at lower velocity and less pressure drop per valve, which can help, but cavitation is fundamentally about the PRESSURE RATIO across the valve relative to vapor pressure, not valve size alone. Anti-cavitation trim (multi-stage pressure letdown, specially shaped internals) is often the more direct fix when the process pressure drop itself is unavoidably severe.