Pressure below atmospheric - the air valve is open and acts to maintain a pressure of zero in the vicinity of the air valve.There are two ways in which an air valve can behave: This approach is typically acceptable for a transient simulation because the transient waves would not propagate past the air gap formed at the air valve.ĭuring the transient simulation, an air valve will always be treated as an air valve. Given the above challenges, the user should consider terminating the system at the high point, using a reservoir or Discharge To Atmosphere node in place of the air valve. It may be necessary to specify the initial conditions manually (by setting the 'Specify Initial Conditions?' Transient Solver calculation option to True - see the Calculation options topic for details - then manually typing in values for the fields grouped under Transient Initial in the Property Editor. The friction factors in the adjacent pipes may also need to be checked, as the head loss computed by the initial conditions calculation may not be a true head loss. Air valves that are open in the initial conditions will need to have the initial air volume defined for transient analysis purposes.If all of the pumps upstream of an air valve are off during a steady state or EPS run, the pressure subnetwork is disconnected in that area and the model will issue warning messages for all nodes in that vicinity indicating that they are disconnected.This can be done by setting the property "Treat air valve as junction" to True for those valves that are expected to remain closed. To improve the stability of the initial conditions, it is desirable to force some of the valves closed. Because air valves have the possibility to switch status during a steady state or EPS, they can lead to instability in the model especially if there are many air valves in the system.
#Water cad surge valves full
Full flow resumes at the point where the hydraulic grade line crosses back above the pipe.
This should be interpreted as a pressure pipe that is not flowing full. This can be displayed as the hydraulic grade line drawn below the pipe. If an air valve becomes open during the initial conditions calculation (steady state or EPS), the hydraulic grade on the downstream side may be less than the pipe elevation.Note that treating an air valve as a junction only applies to the initial conditions (steady state or EPS) the air valve will always be treated as an air valve during a transient simulation. The "Treat air valve as junction" property must be set to "false".
In the rare event that a user needs to model an air valve that is open during the initial conditions, there are several things to note: Pressure at the air valve is above atmospheric pressure and the node acts as a junction.
When air valves are used for transient protection purposes, they are typically closed during the simulation to establish initial conditions (steady state or EPS).
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