What is the maximum percentage a fire pump's rated pressure is permitted to produce at churn condition?

According to NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, a centrifugal fire pump must meet specific performance criteria. One of these criteria defines the pump's performance at zero flow, which is known as the "churn" or "shutoff" condition. The standard mandates that the pressure (head) developed by the pump at this condition shall not exceed 140 percent of its rated pressure (head). This upper limit is crucial for preventing over-pressurization of the fire protection system piping and components when the pump is operating without any discharge.

A. 65 percent: This is the minimum allowable pressure at 150 percent of the pump's rated flow, not the maximum pressure at churn.

B. 100 percent: This is the required pressure at 100 percent of the pump's rated flow, which defines the pump's rating point.

C. 120 percent: This value is not the specified maximum churn pressure for a standard constant-speed fire pump according to NFPA 20.

1. NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, 2022 Edition.

Section 4.10.2.1 Performance. "A centrifugal fire pump for fire protection shall be selected to have a characteristic curve such that the shutoff head does not exceed 140 percent of the rated head..."

2. SFPE Handbook of Fire Protection Engineering, 5th Edition.

Chapter 20, "Water-Based Fire Suppression: Automatic Sprinkler Systems," Section 20.5.2.1, "Centrifugal Pumps." "The performance characteristics of a fire pump are defined by three points on its characteristic curve... The shutoff head shall not exceed 140% of the rated head." (DOI: 10.1007/978-1-4939-2562-420)

3. Oklahoma State University, School of Fire Protection and Safety Engineering Technology.

Courseware for FSET 4583, "Fire Pump & Standpipe Systems." Lecture notes on Fire Pump Characteristics consistently cite the NFPA 20 requirement: "Shutoff (Churn) Pressure: 0% of rated flow, pressure not to exceed 140% of rated pressure."