The PAT transitions between the turbine and decoupled operating conditions in two situations: when manually decoupled or whenever the power generated is equal to zero. The PAT cannot recouple after becoming decoupled during a simulation.

The first transition from coupled to decoupled is referred to as Load Rejection and can be set as a transient event in the Transient tab of the Pump Properties window.

When this transient event is initiated, the PAT is immediately uncoupled from its motor at the onset of the transient simulation, the speed is allowed to change as dictated by the fluid, and the PAT speed is determined for each time based on the No Load Curve. The uncoupling event occurs instantaneously and the PAT will immediately begin operating on the No Load Curve at steady-state.

The second transition from coupled to decoupled occurs when the PAT reaches the No Load point due to other transient events in the system. This transient event is always ready to occur regardless of the transients defined for the PAT. When the flow rate through the PAT becomes low enough such that zero power is generated by the PAT, the PAT will immediately become uncoupled from the motor and become free-spinning with its speed determined by the system flow rate and the No Load Curve.

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