Using a Flow Control Valve (FCV)

Applies To:
Product(s): WaterGEMS, WaterCAD
Version(s): V8i, CONNECT Edition
Area:  Modeling
Original Author Tom Walski

What is a Flow Control Valve (FCV)?

A flow control valve (FCV) in WaterGEMS/WaterCAD is a model element that limits the flow to a specific value specified by the user. It does this by increasing head loss through the valve (throttling). If the system cannot provide that flow, it behaves as it is fully open, and gives a warning that it cannot deliver the flow.

The WaterGEMS FCVs are a subset of all real valves that control flow. (Actually any valve that controls flow can be considered a flow control valve such as the faucet of your kitchen sink.) There are numerous small flow control devices in industrial and irrigation practice (e.g. limit flow from a sprinkler) that also control flow. In large water system applications, an FCV is a single device or collection of components that has

  1. Flow meter
  2. Signal sent to a controller (Programmable Logic Controller)
  3. Mechanical actuator (positioner) to the adjust valve to correct valve setting
  4. Control valve (usually globe body)
  5. Power supply
  6. Connection to SCADA system (optional) 

These valves tend to be quite expensive when compared with hydraulically controlled valves such as pressure reducing valves (PRV) and pressure sustaining valves (PSV). Altitude valves at tanks, PRVs and PSV are referred to as “automatic control valves” and don’t require power. As such, real FCVs are rarely used in water distribution systems. For more complex operations a throttling control valve (TCV) is usually a better representation in a model.

Some engineers think they need FCVs to protect an upstream system (or zone) from having too much water taken from it, thus affecting customers in the upstream system. A PSV can do this more effectively at a lower cost. If an FCV is used, how does the operator select the correct value for the setting?

Some engineers have used FCVs to force a model to look calibrated even when there are other problems with the models. This is poor practice. 

In general, it is best not to use an FCV element in a water distribution model unless it is a real flow control valve with the six components listed above.

For more advice on flow control valves, see the Blog post below:

See Also

(Blog) Death To Flow Control Valves

Using Modulating PRV, PSV or FCV during a transient simulation

Why do I see such a large headloss through my FCV, PSV or PRV?