How can I model a surge anticipator (SAV) or surge relief valve (SRV) that opens between the pipes, not to the atmosphere? Or, a surge valve that is controlled by pressure conditions elsewhere in the system?
The surge valve node element only discharges to the atmosphere when it opens, and only senses pressure at the surge valve location. If you need to model a surge valve that opens between two pipes when a threshold is reached, or if it is controlled by pressure somewhere else in the system, you would need to model this with a Throttle Control Valve (TCV) connected to a Discharge-to-Atmosphere (D2A) element.
The TCV gives you more flexibility with the characteristics and rate of closure. See more here: Modeling Reference - Valve Closure
Start by running a transient simulation with the TCV closed the whole time (fixed pattern, initially closed). Check the pressure time history at the appropriate adjacent pipe end point to see the exact time when the desired threshold is reached. Then, build a transient valve operating rule based on that time. Basically have the pattern start with the valve closed until the time that you recorded, then have it start opening.
Then, do another transient run to see when the pressure subsequently reaches the condition to re-close the valve, then adjust the pattern appropriately, unless you will assume a specific amount of time that the valve stays open.
Related Enhancement # 1056290 (for adding an option to have a surge valve open between pipes)
Modeling Reference - Surge Valves
Modeling existing valves using a TCV in HAMMER