How are headlosses determined for TCV's with the different initial status settings?

  Applies To 
  Product(s):
WaterGEMS, HAMMER, WaterCAD
  Version(s): 08.11.XX.XX, 10.XX.XX.XX
  Area:  Calculations
  Original Author: Mark Pachlhofer, Bentley Technical Support Group

Problem

How are steady state or EPS headlosses determined for the TCV element, for each of the different initial status settings?

Solution

Coefficient Type = Headloss Coefficient

Status = Active

A TCV with a Status of 'Active' means the valve is partially closed and derives it's headloss from the "Headloss Coefficient". The Minor Loss Coefficient field represents the fully open conditions and as such in this case it is only used to determine the Relative Closure, which is important to align with the starting relative closure of a transient operating rule (for Bentley HAMMER). The relative closure is determined by comparing the headloss coefficient to the minor loss coefficient on the curve defined by the Valve Type field.

Status = Inactive

When the Status is 'Inactive' the valve is fully open and the headloss is determined by the Minor Loss Coefficient. In this case the Headloss Coefficient is not used to determine the headloss and it is known that the relative closure is 0%.

In terms of headloss calculations, the initial settings headloss coefficient is the same as the physical minor loss coefficient setting. Meaning, they are both the "K" in the standard headloss equation Hl = KV^2/2g

Coefficient Type = Discharge Coefficient

Status = Active

A TCV with a Status of 'Active' means the valve is partially closed and derives it's headloss from the "Discharge Coefficient (Initial)". In this case the "Discharge Coefficient (fully open)" is not used.

Status = Inactive

When the Status is 'Inactive' the valve is fully open and the headloss is determined by the "Discharge Coefficient (fully open)". In this case the Headloss Coefficient is ignored.

Coefficient Type = Valve Characteristics Curve

Status = Active

A TCV with a Status of 'Active' means the valve is partially closed and derives it's headloss from the "Relative Closure (Initial)". A relationship between Relative Closure and relative discharge coefficient is established based on the selected "Valve Type". The relative discharge coefficient considers the "Discharge Coefficient (Fully Open)" to determine the discharge coefficient for the selected position (Relative Closure (Initial)).

Status = Inactive

When the Status is 'Inactive' the valve is fully open and the headloss is determined by the "Discharge Coefficient (fully open)". In this case the Headloss Coefficient is ignored.

See Also

Modeling an existing valves as throttle control valves in HAMMER

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