I know this is quite late compared to the timing of the other replies, but I just have to add that I purchased Bentley Systems / Haestad Methods HAMMER transient software this Spring (2005). I have run many iterations of both complex and simple water hammer models and have found the program to be quite poorly documented, and it appears to give erroneous results when air valves are admitting air.
For instance, I entered a simple system of one high service reservoir connected by a 10,000 ft long 24 inch diameter pipe to another lower one. Just after the source reservoir I put in a line valve to shut off the water. Downstream of the line valve I put in an air valve to admit air when the line valve is closed.
When the valve was closed, either quickly or slowly, to shut off the water, air would enter the pipe as expected. BUT what is really strange is that air continues to enter the pipe for as long as the simulation continues - way past the total volume of the pipe itself.
Even more interesting is the fact that the pipe in my trial model continued to flow 45 cfs as long as the model continued. Hmmmm With the line valve shut, no water should be flowing after the total pipe volume has reached the downstream reservoir.
This is an obvious problem in this simple model, but my concern is how this affects the transients of systems where a half a dozen air valves are letting air in and the additional air and continued water flow issues are not readily apparent!
I have contacted the Bentley Support folks, and have waited for an answer on this puzzeling issue and am now in my 3rd business day so far including over a weeked, without an answer. I can only imagine the red faces, but I wonder if the recent heat wave in the midwest might not be partially due to glow of emabarrassment and frustration at the Bentley offices?
