Choosing a Check Valve | Bishop Engineering

Q: Which standards or codes apply?

API 594 (check valves), API 6D (pipeline), ASME B16.34 (ratings), API 598 (testing); transient/surge analysis for critical pump lines.

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Quick pick (TL;DR)

Steady flow, large bore → swing.
Pulsating or vertical → dual-plate (spring).
Pump/compressor discharge that can trip → spring dual-plate or axial nozzle (non-slam).
Small bore / high pressure → lift/piston.
Always size so normal flow keeps the disc fully open.

The real problem: flutter & water hammer

Oversizing → flutter; slow closure on a pump trip → slam. Size for full-open and pick non-slam closure.

Step 1 — Gather the input data

Size, normal & minimum flow, density ρ.
What it protects & trip scenario.
Orientation & straight length.
Design P/T, material, connection, class.

Step 2 — Type comparison

Type	Best for	Watch out
Swing	Steady flow, low ΔP.	Slam; needs min velocity.
Dual-plate	Compact, fast, any orientation.	Spring fatigue.
Lift / piston	Small bore, high pressure.	Higher ΔP.
Axial / nozzle	Critical discharge — non-slam.	Highest cost.

Step 3 — Size it: keep the disc fully open

A check needs a minimum velocity to stay fully open. Crane rule for a swing check:

Minimum full-open velocity v_min = 35 / √ρ (v in ft/s, ρ in lb/ft³) water: v_min = 35 / √62.4 = 4.4 ft/s = ~1.35 m/s

Worked example — DN150 water

Given DN150 (ID ≈ 0.15 m) , water , normal Q = 100 m³/h Step 1 — Area A = (π/4) × 0.15² = 0.01767 m² Step 2 — Operating velocity v = (100/3600) / 0.01767 = 1.57 m/s Step 3 — Compare 1.57 > 1.35 m/s → swing check stays open ✓ OK If flow drops to 60 m³/h v = (60/3600)/0.01767 = 0.94 m/s < 1.35 → flutter risk → use spring dual-plate instead

Minimum-velocity calculator

Full-lift velocity check

v_min ≈ 35/√ρ — below it the disc flutters.

ρ (kg/m³)

Line size (mm)

Normal flow (m³/h)

Coefficient

If v < v_min the disc flutters — downsize or use a spring-assisted type.

Step 4 — Acceptance & failure modes

Symptom	Cause & fix
Bang on pump stop	Slow closure → non-slam check + surge study.
Chatter / wear	Oversized → downsize / spring.
Reverse leakage	Debris/worn seat → soft seat + strainer.

Seat verified by API 598; critical lines also need surge analysis.

Step 5 — Installation

Flow arrow; swing only horizontal / vertical-up.
≥ 5 diameters from pump/elbow.
Close to pump discharge on trip lines.

Requisition checklist

Type, size, class, end connection.
Body/disc/seat; spring & material.
Test class (API 598/594); fire-safe/NACE.
Record on the valve datasheet (Function = Check).

Frequently asked questions

What should I know about Choosing & Sizing a Check Valve?

Steady flow, large bore → swing. Pulsating or vertical → dual-plate (spring). Pump/compressor discharge that can trip → spring dual-plate or axial nozzle (non-slam). Small bore / high pressure → lift/piston. Always size so normal flow keeps the disc fully open.

Which standards or codes apply?