Calculating A Reasonable Safety Factor when Sizing Control Valves & Regulators

Correctly sizing a control valve or regulator is essential for safe, stable, and cost-effective operation. A key part of this process is selecting a reasonable safety factor. The goal is to ensure reliable performance without oversizing, which can increase cost and cause process instability. The following guide explains calculating a reasonable safety factor when sizing control valves & regulators.

What is a Safety Factor?

A safety factor is the margin built into a design to ensure that a component, valve, or regulator can handle more than the expected load or operating condition.

Why a Safety Factor Matters

The most often question asked by process engineers, “How do I calculate a safety factor when sizing a control valve or regulator?” It is important to include a reasonable safety factor when sizing. At the same time, be sure to avoid an excessive safety factor as it can be expensive (purchasing a larger valve than required) and lead to instability in the process.

Ideally,

• Pressure regulating valves (PRV) should operate between 30% and 70% open
• Control valves between 20% and 80% open

Your minimum and maximum flow rates should fall close to or within these operating ranges for best performance.

Safety Factor Calculation Formula

Safety Factor for Valve Sizing = Required Cv / Calculated Cv

Expanded Formula:

Many sizing programs calculate the actual Cv required. When sizing the valve types listed below, the calculated Cv should be divided by the corresponding value / safety factor range.

• PRV (pressure regulator): 0.7
• BPRV (back pressure regulator): 0.5
• PPRV/PBPRV (piloted PRV/BPRV): 0.9
• TCV (temperature regulator): 0.9
• DCV (diaphragm operated control valve): 0.9
• MOV (motor operated control valve): 0.9

This practice will ensure you have a reasonable safety factor.

Sizing Softwares to Support Accurate Valve Selection

Our sizing program, JVCV, is available by going to our sizing page. For your convenience, two versions are available, a downloadable version and a web based version.

Available Sizing Programs

• JVCV: Used for Jordan Valve industrial control valves and regulators.
• SVCV: Used for Steriflow sanitary control valves and regulators applied primarily in the Pharmaceutical and Bio-Pharmaceutical industries.
• LVCV: Used for sizing LowFlow fractional flow control valves and regulators.

Multiple outputs are available from each of these programs.

You can find our other sizing programs by visiting,

• www.steriflowvalve.com
• www.lowflowvalve.com