Valve Pressure Drop Calculator
Calculate pressure drop (ΔP) across valves and analyze cavitation/flashing risk. See the effect of valve undersizing on system pressure and pump requirements.
Liquid Pressure Drop
Basic Formula: ΔP = (Q / Cv)² × SG
ΔP = Pressure drop (psi) | Q = Flow rate (GPM) | Cv = Flow coefficient | SG = Specific gravity
Velocity Check: v = Q / (2.448 × A) where A = pipe cross-section (in²)
ΔP = Pressure drop (psi) | Q = Flow rate (GPM) | Cv = Flow coefficient | SG = Specific gravity
Velocity Check: v = Q / (2.448 × A) where A = pipe cross-section (in²)
US GPM
Flow coefficient
Water = 1.0
psia (for cavitation check)
Common vapor pressures: Water at 100°F = 0.95 psia | Water at 150°F = 3.72 psia | Diesel at 100°F = 0.02 psia | Propane at 100°F = 188 psia. Check manufacturer data for your fluid.
Pressure Drop Result
Pressure Drop (ΔP)–
ΔP as % of Inlet Pressure–
Flow Velocity (estimated)–
Recovery Pressure Ratio–
Cavitation Index (σ)–
Gas Pressure Drop
Subcritical Flow: ΔP = (Q / (1360 × Cv × Y))² × (M × T × Z) / P1
Critical Flow (choked): ΔP = 0.528 × P1
Q = flow (SCFH) | M = mol weight | T = temp (°R) | P1 = upstream (psia) | Y = expansion factor
Critical Flow (choked): ΔP = 0.528 × P1
Q = flow (SCFH) | M = mol weight | T = temp (°R) | P1 = upstream (psia) | Y = expansion factor
SCFH (standard cubic ft/hr)
Flow coefficient
psia
°F
Air = 29
Air = 1.4
Gas Pressure Drop Result
Pressure Drop (ΔP)–
Pressure Ratio (x = ΔP/P1)–
Flow Regime–
Expansion Factor (Y)–
Steam Pressure Drop
Saturated Steam: ΔP = (W / (46.2 × Cv))² × (1 / P2)
Superheated: ΔP = (W / (46.2 × Cv × (1 + 0.00065 × T_sh)))² × (1 / P2)
W = steam flow (lb/hr) | P2 = downstream pressure (psia) | T_sh = superheat (°F)
Superheated: ΔP = (W / (46.2 × Cv × (1 + 0.00065 × T_sh)))² × (1 / P2)
W = steam flow (lb/hr) | P2 = downstream pressure (psia) | T_sh = superheat (°F)
lb/hr
Flow coefficient
psig
psig
Steam Pressure Drop Result
Pressure Drop (ΔP)–
Inlet Absolute Pressure–
Outlet Absolute Pressure–
Critical ΔP (58% of P1)–
Flow Regime–
Effect of Undersizing
See how selecting a valve that's too small affects pressure drop and system performance:
GPM
Multiple of required Cv (1.0-2.0)
Cv Cascade: Industry best practice is to select a valve where required Cv is 60-80% of valve's rated Cv at full open. A cascade factor of 1.25-1.5 means the valve is somewhat oversized (good for control). Below 1.0 = undersizing = problems.
Undersizing Impact Analysis
Required Cv (at design flow)–
Selected Valve Cv (× cascade)–
ΔP with Selected Valve–
Extra Pump Head Needed–
Cavitation Risk–
Control Quality–
Understanding Valve Pressure Drop
Key Concepts
- ΔP (Delta P): Pressure difference between inlet and outlet of the valve
- Cv (Flow Coefficient): Measures valve flow capacity. Higher Cv = lower ΔP for same flow
- Cavitation: When local pressure drops below vapor pressure, causing bubble formation and collapse damage
- Flashing: Permanent vaporization when downstream pressure is below vapor pressure
- Choked Flow: Maximum flow condition where further downstream pressure reduction doesn't increase flow
Acceptable ΔP Guidelines
- Liquid: 10-30% of inlet pressure typical. Above 50% indicates undersizing.
- Gas: 10-50% of inlet pressure. Above 50% may cause noise/compression issues.
- Steam: Below critical ratio (ΔP/P1 < 0.58) for stable flow. Above = choked flow.
Need Help with Valve Sizing?
Our engineers can size valves to minimize pressure drop and avoid cavitation. Send your process parameters.