Filling Pipe

Hello Charles,

I assume you're referring to a surge that may occur after air has been expelled from an empty pipe.

HAMMER does have limited capabilities to model air at discrete points in the system. If you have the latest version of HAMMER, (08.11.01.32) check out the "Inrush" scenario in the Discharge_To_Atmosphere.wtg sample file. This illustrates how to model an initial air pocket at the end of a system, which is then expelled during the transient simulation. As seen in the sample file, this is typically done by using the "Gas Volume (Initial)" field in the properties of the discharge to atmosphere element. The "typical flow" and corresponding "typical head drop" are used to establish the relationship between water pressure and flow at the end of the system.

I'd like to add though that in my opinion, the larger the amount of air you introduce into a HAMMER model, the less accurate the results may be, since you're deviating further from normal transient theory. Be sure to read the help topics on the assumptions made with air/vapor in a transient simulation.

Hi Jesse:

Thanks for your post.

Really, I am trying to find out if Hammer is able to verify the behaivor of pipe and air valves, when you are filling the pipe; for example, if the air valve´s setting along the pipe, is suitable to avoid waterhammer.

Charles

Hi Jesse:

Thanks for your post.

Really, I am trying to find out if Hammer is able to verify the behaivor of pipe and air valves, when you are filling the pipe; for example, if the air valve´s setting along the pipe, is suitable to avoid waterhammer.

Charles

Hi Charles,

HAMMER won't model a pipe filling from completely empty - the HAMMER calculations require that the pipe is predominantly full and under pressure.

However you could model the final stages of the filling process to check your air valves. Some notes:

- It is probably easiest to set this up if you model the pipeline full to start with, then let it drain for a while so that air enters the air valves, then start to refill the pipeline again.

- Alternatively you can start the model with some air in the pipelines. At the air valve elements, set "Air Volume (Initial)" value to something greater than zero (you will need to estimate a reasonable value here). Also, you will need to make sure the initial pressure at the air valve is zero, and the only way to do that is enter all of the initial conditions manually (go to Analysis > Calculation Options > Transient Solver > double click to edit the current set of Calculation Options > set 'Specify Initial Conditions' to True, then enter the initial flow and hydraulic grade line values for each pipe. This can be time consuming, which is why I would initially try the approach I mentioned first.

Hope that helps.

Regards,

Mal Sharkey