You are currently reviewing an older revision of this page.
When computing a transient simulation with an emergency pump shutdown, no matter what surge protection I try to put in place, it does not seem to help with negative pressures.
Take a close look at the profile of your system. If you're pumping over a hill and the boundary conditions on either end of the system are lower, than it may not be possible to maintain a positive pressure, so long as the pump(s) remain off. Basically when the pump turns off and the HGL drops, even if you had multiple tanks along the pipeline, they may help protect the system at first, but will eventually drain out and cause the HGL to drop to low levels. This can cause vapor pocket formation. When vapor pockets collapse, they can cause severe pressure spikes (or "upsurges").
You may need to consider how long the pumps will be off and size the surge protection device(s) based on that. You can use the "variable speed" transient pump type to simulate the pump turning off and then back on, or consider two runs (one for shutdown and the other for start up). There may be concerns with how fast any trapped air is released upon startup.