A swing check valve uses a hinged disc to permit forward flow and oppose reverse flow. This calculator gives a liquid Cv requirement for an entered pressure-drop scenario and nominal velocity through an entered internal pipe diameter. It does not predict disc opening, closure dynamics or suitability for a service.
Horizontal Swing Check Valve Interactive Calculator
Calculate a required full-open liquid Cv scenario from entered flow, specific gravity and pressure drop, plus nominal velocity from entered internal diameter.
Equation Used
- Steady incompressible liquid with entered specific gravity.
- Entered pressure drop is the allowed full-open valve loss for the scenario.
- Entered diameter is effective internal circular flow diameter for nominal line velocity.
- No valve-specific opening curve, disc mass, hinge friction, cracking head, transient reversal, slam, cavitation, erosion, materials or pressure-temperature rating.
Disc opening and risk are not calculated. These require the actual valve’s geometry, force balance and flow/dynamic data. A Cv requirement and nominal line velocity alone cannot establish stable opening, wear or safe selection.
Generic one-way valve concept
A hinged disc can move away from a seat under forward-flow forces and return toward the seat under gravity and reverse differential pressure. Exact motion depends on valve-specific geometry and dynamics.
The animation is qualitative. It follows a fixed motion cycle and does not solve disc position from the flow inputs.
Use as a preliminary liquid-flow conversion
The Cv and velocity identities can screen entered scenarios. They cannot select a valve or establish orientation, minimum stable flow, closure response, pressure class or service compatibility.
Liquid Cv and nominal velocity
Rearranging ΔP=SG(Q/Cv)² gives Cv=Q√(SG/ΔP). For Q in US gpm and internal diameter d in inches, nominal circular-pipe velocity is approximately 0.4085Q/d² ft/s.
Disc position cannot be inferred from line velocity alone. The simplified liquid relationship also omits viscosity corrections, choking and cavitation analysis.
Worked example
At 80 gpm, SG=1.0 and allowed full-open drop 0.5 psi, required Cv is about 113.1. With 2.0 in effective internal diameter, nominal line velocity is about 8.17 ft/s.
Scope and limitations
Selection requires the actual manufacturer's Cv versus disc position, minimum stable-flow data, cracking and reseat characteristics, orientation approval, pressure-temperature rating, materials compatibility, solids and viscosity, pump/system curves and transient analysis for reversal and water hammer.
Frequently asked questions
Does the calculator predict disc opening?
No. The disc-opening and risk outputs state Not calculated because there is no valve-specific force balance or dynamic model.
Does required Cv select nominal size?
No. It is a flow-coefficient requirement under the stated liquid assumptions. Selection also needs manufacturer flow and dynamic data and the actual service conditions.
Can this model steam or gas?
No. The Cv expression used here is for a simplified incompressible-liquid scenario.
Does internal pipe diameter equal valve nominal size?
Not necessarily. The velocity calculation uses the entered internal circular diameter; valve passages and nominal connection sizes can differ.
Is the pictured movement controlled by the flow input?
No. It is a qualitative repeating illustration, not a simulation of flow-driven opening or closure.
Flow relation and valve data
Swagelok: Valve Sizing Technical Bulletin explains flow-coefficient equations and fluid-specific variables. The calculator uses the basic liquid relation in US customary units, without viscosity or choked-flow corrections.
Val-Matic Engineering Manual discusses check-valve opening and dynamic behavior. Those characteristics depend on the valve and system; they are not represented by the two numerical flow results here.
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