Check Valve Sizing Calculator

Calculator Inputs

Formula Used

This tool uses the standard liquid sizing relationship between flow, pressure drop, and valve capacity. For a quick check valve selection, it compares the Cv you need against typical Cv values by nominal size.

• US units: Cv = Q / √(ΔP / SG), where Q is gpm and ΔP is psi.
• SI units: Kv = Q / √(ΔP / SG), where Q is m³/h and ΔP is bar.
• Conversion: Cv ≈ 1.156 × Kv.
• Reverse check: ΔP = SG × (Q / Cv)² (or the Kv equivalent in SI).

Style factor adjusts available Cv to reflect different internal designs and losses.

How to Use This Calculator

1. Select your unit system and enter the design flow rate.
2. Enter fluid specific gravity and the allowable pressure drop across the check valve.
3. Choose the valve style that best matches your project specification.
4. Submit to see required Cv, a suggested nominal size, and estimated pressure loss.
5. Review the velocity advisory and confirm with manufacturer Cv tables.
6. Download CSV or PDF to include in submittals and calculations.

Example Data Table

Examples are illustrative; confirm with actual valve Cv and project criteria.

Professional Guide: Check Valve Sizing in Building Systems

Check valves protect building piping by allowing flow in one direction while reducing the chance of backflow, pump reverse rotation, and unwanted drain-down. In domestic water, chilled water, condenser water, and fire protection branches, the most common sizing mistake is selecting a valve only by pipe diameter. A check valve behaves like a flow restriction, so performance depends on the valve’s capacity rating and the allowable pressure loss in your design.

Capacity is commonly expressed as Cv (or Kv in metric). Cv links flow rate and pressure drop, letting you estimate whether the valve will pass the required flow without consuming too much system head. When the valve is undersized, pressure loss rises quickly, reducing delivered flow and increasing pump energy. When the valve is oversized, the disc may chatter, close slowly, or fail to stabilize at low velocity, which can increase wear and noise.

Practical sizing also checks velocity. Higher velocity can increase noise, vibration, and water hammer severity during rapid closure events. Low velocity can reduce self-cleaning and may allow debris to settle at the seat. A balanced selection targets your project’s acceptable ΔP while keeping velocity in a comfortable range for the service, material, and expected solids content.

This calculator estimates the required Cv from your design flow, specific gravity, and allowable pressure drop. It then compares that requirement with typical Cv values by nominal size, adjusted by an internal style factor. Use the result as a screening step, then confirm the final selection against the manufacturer’s published Cv curve for the exact valve model, pattern, and end connections.

Worked example

Suppose a domestic water riser requires 250 gpm, with SG = 1.00 and allowable ΔP = 5 psi. The required capacity is: Cv = 250 / √(5/1.00) ≈ 111.8. A swing-style valve typically meets this around a 3 in nominal size using representative Cv data. The calculator also reports an approximate line velocity using a typical Schedule 40 inside diameter to support a quick reasonableness check.

For critical systems, also evaluate minimum cracking pressure, installation orientation, accessibility for maintenance, and the risk of slam during pump trips. When surge is a concern, consider faster-closing designs, damped mechanisms, or a detailed transient analysis. In fire protection lines, coordinate valve loss with hydraulic calculations and verify that the selected check valve meets listing requirements, orientation limits, and inspection access needs.

FAQs

1) What does Cv mean for a check valve?

Cv is a capacity rating that relates flow to pressure drop for liquids. Higher Cv means less restriction at a given flow. Always confirm the exact Cv from the chosen manufacturer and model.

2) Should the check valve always match the pipe size?

Not always. Matching the pipe can work, but it may over- or under-restrict flow. Use allowable pressure drop, expected flow, and stability at low flow to select an appropriate size.

3) Why does valve style change the result?

Different designs create different internal losses. Swing valves often have lower losses than lift or piston designs. The style factor in this tool is a simplification to reflect that behavior.

4) What velocity is acceptable in building piping?

It depends on service, material, and noise limits. Many designs aim for moderate velocities to reduce erosion and water hammer risk. Use your project criteria and local standards for final limits.

5) Can I use this for steam or compressed air?

You can use it as a rough screen, but gas sizing is more complex because density changes with pressure and temperature. For final selection, use manufacturer gas equations and service conditions.

6) What is cracking pressure and why does it matter?

Cracking pressure is the differential pressure required to start opening the valve. If it is too high, low-flow branches may not open fully. Check published data when flows can be small.

7) How should I finalize a check valve selection?

Confirm Cv on the exact model, verify ΔP at design and minimum flow, check installation orientation and maintenance access, and evaluate surge risk. Document the basis and export results for review.