If system pressure drops to the fluid’s vapor pressure, the fluid flashes into vapor, resulting in a separation of the liquid columns. Consequently, vapor pressure is a fundamental parameter for hydraulic transient modeling. Vapor pressure changes significantly at high temperature, operating pressure, or altitude. Fortunately, it remains close to HAMMER CONNECT’s default value for a wide range of these variables for typical water pipelines and networks.

If your system is at high altitude or if it is an industrial system operating at high temperatures or pressures, consult a steam table or vapor-pressure curve for the liquid. Consider a few extra model runs to assess the sensitivity of the hydraulic transient simulation results to global changes in vapor pressure—you can change it on the System tab of the Options window (Tools > Options).