Modelling float valve at tank (inlet valve throttle?)

Sayed,

The Discharge Coefficient (sometimes referred to as a "valve coefficient" or "Cv") is used to model the relationship between flow and headloss through the tank's float valve. It is This is important as the valve starts to throttle (to close the inlet pipe). The value to enter depends on the valve, so you may be able to obtain it from the manufacturer.

If this is not available, but you have the minor loss coefficient for the valve (K), then you can use the below equation:

K = Cf D^4 / Cv^2

where D = diameter (in., m)

Cv = valve coefficient [gpm/(psi)0.5, (m3/s)/(kPa)0.5]

Cf = unit conversion factor (880 English, 1.22 SI)

Furthermore, if still unsure, you could perform a sensitivity analysis, trying a range of reasonable values and checking the response. If the results that matter to you are not significantly effected, then you may not need to worry about how accurate the discharge coefficient is.

Hi Jesse

Thanks a lot for this explanation for discharge coefficient. I wonder if you could provide me with simple model showing how to use inlet tank throttles? To control filling of elevated tank? Wirh explanation in steps

Regards Eng. Sayed Elhagar

Attached is a modified version of the "Example5" model, using the top filling tank and throttling inlet valve features on tank T-1. Some details to help explain how I set it up and how it's working:

- Maximum tank level: 31.6 m.
- Invert of inlet pipe: 31.2 m (just below the top)
- level inlet valve starts to close: 30.2 m (1 m below the pipe)
- level inlet valve fully closed: 31.0 m (just below the pipe level)
- discharge coefficient (fully open) : 0.05 m^3/s/mH2O^0.5 (arbitrary)

With the pump on/off control disabled, the pump is always on. When the tank gets above 30.2 m, the inlet float valve starts to close the inlet pipe, preventing the tank from becoming full. During this time, the pump flow decreases since less water is filling the tank. As demand increases and the tank starts to drain more, the inlet valve opens back up and the pump flow increases. Take a look at the two saved graphs for more details.

Note that this model is saved in version 08.11.05.61 format.

I've also gathered together some information from various sources on these features and documented them along with this example model in the below Support Solution:

Modeling top fill tanks and throttling inlet valves

Attached is a modified version of the "Example5" model, using the top filling tank and throttling inlet valve features on tank T-1. Some details to help explain how I set it up and how it's working:

- Maximum tank level: 31.6 m.
- Invert of inlet pipe: 31.2 m (just below the top)
- level inlet valve starts to close: 30.2 m (1 m below the pipe)
- level inlet valve fully closed: 31.0 m (just below the pipe level)
- discharge coefficient (fully open) : 0.05 m^3/s/mH2O^0.5 (arbitrary)

With the pump on/off control disabled, the pump is always on. When the tank gets above 30.2 m, the inlet float valve starts to close the inlet pipe, preventing the tank from becoming full. During this time, the pump flow decreases since less water is filling the tank. As demand increases and the tank starts to drain more, the inlet valve opens back up and the pump flow increases. Take a look at the two saved graphs for more details.

Note that this model is saved in version 08.11.05.61 format.

I've also gathered together some information from various sources on these features and documented them along with this example model in the below Support Solution:

Modeling top fill tanks and throttling inlet valves