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Industry Term of the week: Pressure Class

What “Pressure Class” Means


  • It’s a rating system (Class 125, 150, 250, 300, 600, 900, etc.) that defines how much pressure the valve can handle.

  • The rating is based on ASME/ANSI standards—most commonly ASME B16.34 and B16.5 for flanges.

  • Higher class = stronger, thicker valve body designed for higher pressures and temperatures.

(NOTE: specifically for Globe valves and ANSI 250)

  • The “Class 250” designation is a pressure class used primarily for flanges and valves made of gray cast iron.

How It Works


  • Each pressure class has an associated pressure-temperature table.
  • As fluid temperature increases, the allowable pressure decreases, even within the same class.
  • Example: A Class 150 valve might be rated for 285 psi at 100°F, But only 150 psi at 400°F.

Why It Matters


  • Ensures the valve body won’t burst or deform under system pressure.
  • Helps match the valve to the system’s piping pressure rating (e.g., if the system uses 150-lb piping, you typically use a Class 150 valve).
  • Avoids code violations in mechanical/HVAC systems.

Control Valve Specifics

Even though control valve sizing depends on Cv and actuator torque, the valve body still must match the system pressure class.

  1. Body pressure class = mechanical integrity
  2. Trim selection = control performance

Common HVAC examples:

  • 2-way and 3-way valves on chilled/hot water: Class 125 or 150
  • Steam control valves: Class 250, 300, or 600, depending on pressure

Rule of Thumb for choosing the right pressure class valve:


Choose a pressure class that:

  • Meets or exceeds system MAWP (maximum allowable working pressure)
  • Matches the piping flange class.

Some Common Selection tips:


  • If you see a valve specified as “Class 125 or 250” you’re probably looking for a flanged Globe valve 2.5in up to 6in.
  • Common Vendors: Belimo, Honeywell, Schneider Electric, Siemens, JCI
  • ANSI class will determine flange bolt pattern and is typically in most specs.
  • Don’t assume 8 bolt flanges are always ANSI 250, they may be for a higher rating as well.
  • You’ll want to verify the flange bolt pattern, valve material (cast iron vs ductile vs steel) and what temperature it will operate at if not provided in the specs
  • In HVAC hydronic systems: If you’re using cast iron valves in moderate pressure, moderate temperature service, a Class 125/250 body may be acceptable—but for higher temperature/pressure or critical service (steam or high-temp water) you’ll likely need a higher class or different material.
   Pressure Class

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