Getting Gate Valve Sizing Right: A Designer’s Guide to Flow, Fit, and Function

Gate valves are fundamental to the performance of water transmission and fire protection systems. As they’re often chosen for their simple design, low pressure drop, and ability to provide full flow with minimal turbulence. However, a critical step often overlooked in system design is to correct valve sizing.

Improper sizing can result in flow restriction, excessive head loss, difficulty in operation, or long-term reliability issues. This guide explains how to select the right gate valve size by integrating hydraulic calculations, system pressure requirements, and installation conditions—ensuring long-term efficiency and safety in the field.

What Does “Correct Size” Actually Mean?

In professional terms, gate valve sizing means determining the valve diameter that will:

• Match the pipeline it connects to

• Handle the system’s design flow and pressure

• Maintain acceptable velocity and head loss

• Comply with regulatory standards (UL, FM, AWWA, ISO)

In most applications, the valve is sized to match the pipe diameter, but that alone isn’t enough. Let’s walk through the details.

Step 1: Match the Nominal Pipe Size

This is the starting point. Gate valves are manufactured to standard nominal diameters (e.g., 2”, 4”, 6”, 8”, 10”, 12”, 16”), and in most cases, the valve should directly correspond to the adjacent pipe diameter.

Examples:

• 6″ underground ductile iron pipe → 6″ gate valve (NRS type)

• 8″ pump header → 8″ OS&Y gate valve or butterfly valve, based on space and flow control needs

Note: Be sure to specify the end connection (flanged, grooved, mechanical joint) to match the piping system. BIMEX valves are available in EN or ANSI B16.1/B16.5 flanged and mechanical joint configurations.

 Step 2: Confirm Flow Rate & Velocity

This is where many specifiers stop short. While matching pipe size is standard, flow conditions must be checked. Gate valves are full-port, but flow performance is still affected by turbulence, seat geometry, and water velocity.

Use the Hazen-Williams formula or system hydraulic modeling software to estimate:

• Maximum flow rate (GPM or L/s)

• Velocity (m/s or ft/s)

• Head loss (m of water or psi)

Design guidance:

• Keep velocity under 3 m/s (10 ft/s) for fire protection systems

• Target head loss < 10% of total system pressure

• For pump discharge lines, higher velocity may be acceptable, but it must be validated

 Step 3: Check System Pressure Rating

Fire protection gate valves—especially for buried systems—must withstand:

• Working pressure (typically up to 250 psi or PN16)

• Test pressure (usually 1.5× working pressure)

All BIMEX gate valves are UL Listed and FM Approved at 250 psi working pressure, tested up to 500 psi. That meets AWWA C515/C509 and global safety codes.

Reminder: Avoid using valves below their pressure class, especially in systems with water hammer risk.

 Step 4: Consider Installation Environment

• Underground: Use NRS (Non-Rising Stem) valves with a tamper switch or post indicator. No stem extension needed; requires less vertical clearance.

• Above Ground: Use OS&Y (Outside Screw & Yoke) for visible stem position. Required in many code-compliant pump rooms.

Also consider:

• Trench width and depth for underground access

• Accessibility for future maintenance

• Clearance for wrenching and operating torque

BIMEX Gate Valve Range

BIMEX offers an extensive line of AWWA-compliant, UL/FM-certified gate valves, ideal for water and fire networks

Standard features include:

• Ductile iron body and bonnet

• Fusion-bonded epoxy coating per AWWA C550 (≥300 µm)

• Stainless steel stem

• Resilient seated wedge

• Double O-ring shaft seal

Sizing Is a Specification—Not an Assumption

Choosing a gate valve size is more than picking a number from a catalog. It’s a technical decision that should factor in pipe size, flow rate, pressure class, and installation conditions. Specifying the wrong valve wastes money at best—and compromises safety at worst.

By working with certified manufacturers like BIMEX and referencing hydraulic and regulatory data, engineers and contractors can make informed choices that ensure system performance and compliance.

Need help sizing a gate valve?
Contact BIMEX for technical datasheets, submittals, or design support tailored to your application.