ESDU 85009 gives a graphical means of estimating the maximum mass inflow rate@ and hence the pressure drop below atmospheric@ through an air inlet/outlet valve following pump trip or valve closure. The maximum volume of air in the resulting air cavity is also predicted@ and hence the time taken for the air to be released on restarting the line. The method assumes a constant diameter liquid-filled line carrying fluid from an upstream sump to a downstream constant pressure point. A program in Basic is also given to provide the information@ and covers the case when the line is additionally protected by an air vessel. The use of the information is illustrated in a practical worked example. Guidance on the use and location of air valves in pipelines for both normal use and surge suppression is included.