How can I model a pump startup followed by a shutdown, or a pump shutdown followed by a startup?
To model a pump start up followed by a shut down, follow the normal steps to model a pump startup using the "Pump Start - Variable speed/torque" Transient pump type (see this article for the steps), but configure your transient operating rule to drop the multiplier back down to zero at the time when the pump shuts down (after some delay). You'll need to decide how long the pump will stay on before shutting down. An initial run with just the pump startup may help, so you can observe when the transient waves settle down.
If your control variable is set to "speed", then similar to the startup portion of the operating rule, the shutdown part would need to simulate how long it takes to spin down. If the control variable is set to Torque, the shutdown part of the operating rule would simulate how long it takes for the power to be disconnected. The starting multiplier would be set to 0 (off - zero speed/torque) In the examples below, for torque, an instant change in torque is assumed for both the startup and shutdown parts of the pattern; "flipping the switch".
For more on torque for speed as the control variable see this article.
Note: if you do not want to assume a check valve in the pump during the transient simulation, enter a large number such as 9999 seconds for the "Time (for valve to operate)".
Startup plus shutdown, control variable as Speed:
Startup plus shutdown, control variable as Torque:
In the reverse case where you want to first simulate an emergency shutdown followed by a startup, you would use the "Variable Speed/Torque" transient pump type and configure the operating rule with a starting multiplier of 1.0, then configure the pattern to shut the pump down, then turn it back on.
As with the first case, you'll also need to decide how long the pump will be off before you turn it back on. In the case of a surge tank or hydropneumatic tank, the tank will need to be sized appropriately for the water to supply the demands and dampen the transient wave for at least the minimum time the pump is off. There may be concerns with how fast any trapped air is released upon startup.
The points about speed vs. torque also apply in this case.
Shutdown plus startup, control variable as Speed:
Shutdown plus startup, control variable as torque:
Modeling A Pump Start-Up Transient Event
Modeling a pump shut down transient event
Pump Startup occurs too quickly / initial upsurge too severe