A Single Stage Air Vacuum Valve takes air in when the pipeline pressure drops below atmospheric and releases air to the atmosphere when the pipeline pressure exceeds atmospheric pressure. The single stage air valve has the same size orifice for inflow and outflow (usually the same orifice). Also an initial volume of air can be specified to model startup with air in the system at the air valve location.

A Two-Stage Air Valve has a different size orifice for inflow and outflow. The outflow orifice is smaller to reduce the rate of air expulsion and the air slam which occurs when all the air is expelled and the liquid columns rejoin. See Air Slam Pressure Calculator to calculate the Air Slam Pressure.

The Air Valve junction elevation should be equal to the center of the pipe elevation.

Disable This Surge Protection Device

If this box is checked, then this surge protection device (SPD) will not be modeled in the current Surge analysis.

Device Type

Select the type of Surge Protection Device to be used.

1 & 2 Stage Air Vacuum Valve Input Data

  • Inflow Diameter - The diameter (mm in SI/ inch in English) of the orifice that allows air to enter the system.

  • Outflow Diameter - The diameter of the orifice (mm in SI/ inch in English) that allows air to exit the system. (For 1 stage air valves, the Inflow and Outflow diameters will be the same).

  • Initial Air Volume - This allows you to specify an air pocket volume (m3 in SI/ ft3 in English) that has accumulated at the valve at the start of the simulation. Normally this value is 0 which means that no air pocket is initially present.

  • Air Valve Delay Time - Air Valve Delay Time is the time for the air valve to activate.

Purge - Use the Purge button to remove existing Data.

Create/Update - Enter new or changed data and exit the dialog box.

Cancel - Cancels any new or changed data and closes the dialog box.