In HAMMER/OpenFlows, relief/surge valves are typically modeled as discharging to atmosphere, or with logic that does not adequately represent “in-line” relief valves (between two pipes) whose actuation depends on the pressure differential between upstream and downstream.
In many real systems—especially control structures and stations with multiple control valves—it is common to use “surge valves between pipes” that open/close based on a ΔP threshold (P_upstream − P_downstream). These valves serve two key operational functions:
relieve upstream overpressure by transferring flow to the downstream side when ΔP exceeds a defined value;
mitigate downstream subpressure (avoiding sub-atmospheric conditions) by allowing flow injection from upstream to downstream when ΔP reaches the threshold in the opposite direction.
Workarounds attempted:
using a TCV between upstream and downstream with manual patterns: difficult to calibrate, because the logic depends simultaneously on P_upstream and P_downstream;
using “Periodic” elements to simulate opening: inconsistent results that do not reflect the expected behavior.
Request:
Please implement a new element (or extend an existing one) to represent a “surge/relief valve between pipes” with:
a differential pressure trigger threshold, ΔP = P_upstream − P_downstream;
the ability to define downstream pressure/condition (not only atmosphere);
modulating opening/closing with rate coefficients (opening/closing rate) and optional hysteresis;
robust numerical stability for transient simulations (avoiding ill-conditioning warnings).
Note:
Specialized transient analysis software such as KYSurge already provides this capability, which shows this is a common arrangement in surge engineering. In its current state, this becomes a relevant limitation of HAMMER for accurate modeling of systems that use in-line relief valves.
Expected benefits:
better physical fidelity when representing ΔP-based protection devices;
fewer workarounds involving manual calibration and instability issues;
improved confidence in predicting subpressures and surge mitigation in control structures.