# Maximum air velocity and flow for Air valves in HAMMER (i.e., Sonic Limit)

 Product(s): HAMMER Version(s): CONNECT Edition, V8i Area: Modeling

# Problem

What is the "sonic limit" for air valve flow rate?

What is the maximum air flow rate in or out of an air valve?

Does HAMMER throttle air flow rate per the sonic limit?

Why am I seeing a very large flow in the pipe adjacent to an air valve?

Why is the velocity or air into or out of my air valve very high?

# Solution

The sonic limit is the highest air flow rate that could occur into or out of an air valve. The throttling at this velocity is due to the speed of sound in air.

Why is the velocity of air into or out of my air valve very high? Why am I seeing a very large flow in the pipe adjacent to an air valve?

The velocity of air through an air valve can be very large, as it is only limited by the speed of sound.

What is the maximum velocity of air into or out of an air valve?

At 60 degrees F, the sonic velocity limit is approximately 340 meters per second, or 1115 feet per second. Air flow rate for an air valve is limited to this speed.

When does an air valve start to throttle the air flow?

An air valve will start to throttle the air flow rate when the air velocity exceeds the "Sonic Limit". See the equation mentioned in the "Air Flow Rate Calculation" section of the "Modeling Reference" article below.