Churn

This clause from the Australian Standard AS 2941-2013 outlines critical considerations for the pressure management of fire protection systems, particularly concerning the maximum allowable pressure within the system as follows;

• Net Pump Shut-off (Churn) Pressure
  This is the pressure the pump produces when operating at zero flow, meaning the discharge valve is fully closed. It's essentially the highest pressure the pump can generate.
• Maximum Static Suction Pressure
  This is the highest pressure in the suction line when the pump is not operating. It accounts for the pressure in the supply system or water source, which can vary depending on the elevation and the specific conditions of the installation.
• Adjusted for Elevation
  Pressure changes with elevation due to the effects of gravity on the water column. This adjustment ensures that the pressure calculations accurately reflect the conditions at the specific elevation where the pump is installed.

The clause mandates that the sum of these pressures must not exceed the pressure rating of the system components, such as pipes, valves, and fittings. This is crucial to prevent potential failures due to overpressure, which could lead to leaks, bursts, or other hazardous situations.

Importantly, the standard specifies that pressure-relief valves should not be used to control or mitigate this combined pressure. Instead, the system should be designed and configured in such a way that the pressures inherently stay within the safe limits for the components, relying on the correct pump selection, system design, and proper adjustment for elevation.