View Full Version : Modelling an Altitude Valve

January 30, 2017, 10:58 AM

Is there an effective way to model an altitude valve in InfoWater? The valve I am modelling is used to control the flow into a cylindrical tank.

My model is very simple - I am essentially trying to determine the pressure at a location on the main line that feeds the tank, prior to the valve. I am trying to determine whether a new connection to this line would have an adverse affect to the existing reservoir.


Patrick Moore
January 30, 2017, 12:31 PM
Adam (aph851) ,

There are several ways one can model an altitude valve in InfoWater. Deciding which is the best way for your model often depends on how the actual valve in the real world operates. If the valve when opened fills the tank at a fairly constant rate you may wish to use flow Control Valve (FCV) in the model with simple controls on it that will open the valve when the tank hits a low level and stop filling the tank at the high level. Or if the valve has a pressure sustaining feature you may wish to model it as a Pressure Sustaining valve (PSV) with similar controls as the FCV. You can also use a Float Valve (FV) in the model where you define the upper and lower levels and the headloss vs flow curve that will control flow through the valve when it is active.

I have found one of the best ways to decide which method is best is to grab SCADA data for the tank level and for flow meters that would impact the tank level (such as pump station flows or other key valve flows) and based on the change in tank level try to determine the rate of flow used to fill the tank to determine what kind of valve would make the most sense. Once you can see how the tank is filling, you can get a better sense of what would best represent that in the model.

You will also need to make sure that you are modeling the altitude valve such that it will allow the tank to drain (perhaps through a check valve around the fill line) so that the closed fill valve will not prevent the tank from being able to drain. This may require you to add some elements to the model to do so under certain circumstances. If the fill line and the "drain" line are separate, you should be fine, but make sure to check this.

One last thing: For any valve controls (and initial status) make sure to use "setting = X' to turn the valve on, rather than Status = OPEN in any control statement or initial status. Valves need a setting to act as a control valve. If you use Status = OPEN, the model will assume the valve is to act as an open pipe and headloss will only be based on the valve minor loss coefficient. This can result in very large flows through the valve.

If you use a float valve and you find the valve is flowing too much, then first determine the head difference between the system and the tank and adjust the headloss on the headloss vs flow curve so induce more headloss and reduce the flow that is filling the tank. Similarly, lower the headloss on the headloss vs. flow curve if there is not enough flow into the tank when using a float valve.

I would recommend using simple controls (looks like a hand on a blue pipe in the model explorer) for the control statements if you use a FCV or PSV to control the valve operation. If you use the float valve, the simple controls are built in on the float valve and you wont need to add additional control statements.

Once you set this up you can run the model and adjust the valve settings or the headloss vs flow curve as needed to get the expected behavior in filling the tank and determine what this would do to the system pressure I assume when the tank is filling.

If you have additional or clarifying statements/questions, please reply to this post.

Patrick Moore

February 10, 2017, 06:43 AM

Essentially I am trying to get a tank to fill at the same rate as it empties, i.e maintaining the same water elevation. I can't seem to get this to happen without the tank creating an additional demand on my transmission main. Is there a simple way to model this without replacing the tank with a fixed head reservoir?


Patrick Moore
February 10, 2017, 07:44 AM

Generally if you want a tank to drain and fill at the same rate, this would essentially keep the tank level constant. The best way I would do that is to model the fill valve as a pressure reducing valve (PRV) without any controls on it. Set the pressure setting of the valve so that it corresponds to the tank level you want the tank to maintain (Example: tank at 100 ft elevation and you want it to stay at 23.1 ft so the HGL for that is 123.1 ft, If the valve is at elevation 100 ft then it needs to maintain a pressure equal to 123.1-100 ft or 23.1 ft. This is then converted to psi as 23.1 ft / 2.31 ft/psi = 10 psi. Set the valve to maintain 10 psi.)

This methodology is about the only way you can generally fill the tank at the same rate the tank drains. With this type of setup there is no need to put any controls on the fill valve as the PRV will automatically adjust the inflow to maintain the tank HGL. Try to have the PRV as close as possible to the tank, but have at least 1 junction between the valve and the tank. As long as the headloss between the valve and the tank is nearly negligible, the water level in the tank should remain constant over the portion of the simulation.

Hope this helps.

Patrick Moore