For horizontal pumps, the nameplate specifies a target pressure difference. What is this pressure called?

• A. Churn
• B. Shutoff pressure
• C. Discharge pressure
• D. Static pressure

Answer: (A)

The key idea is the starting pressure the pump must develop before water is flowing. For horizontal fire pumps, the nameplate lists a target pressure difference that the pump should reach as it starts up with the discharge valve closed—that initial pressure rise is called the churn pressure. It reflects the pump’s ability to build head quickly from rest.

This isn’t the discharge pressure (that’s measured under flow), nor the static pressure (pressure with no flow in the system), and while shutoff pressure involves zero flow too, the term used on the horizontal pump nameplate for the start-up target is churn. So the specified pressure difference you’re looking for is the churn pressure.