| Product(s): | WaterGEMS, WaterCAD, HAMMER |
| Version(s): | 10.04.00.108 |
| Area: | Calculations |
Problem
When using a General Purpose Valve (GPV), Turbine or Orifice-Between-Pipes (orifice) element with the version 2.2 solver (available starting with CONNECT Edition Update 4), the calculated headloss is very large and does not follow the GPV headloss curve.
Solution
This was a known issue (reference # 1007829) with version 10.04.00.108 when using the 2.2 solver version (selected in the calculation options).
This has been fixed for the 2023 release (23.00.00.16) and the fix will be in higher versions as well. For information on upgrading, see:
If you are unable to upgrade and must stay on version 10.04.00.108, a workaround is to select the earlier solver from the Engine Compatibility field in the calculation options (Home > Options), such as WaterGEMS 2.0.012.
A note on Transient simulation handling of GPVs
Note that the GPV element will not work the same during a transient simulation in HAMMER. During a steady state or EPS, it uses the flow vs. headloss curve, but during the transient simulation HAMMER always uses the pair of initial flow and initial headloss through each valve element, to calculate a discharge coefficient which it uses during the transient simulation. This means that the headloss through the GPV during the transient simulation will not necessarily follow your GPV headloss curve, as the flow changes. This can be especially noticed with a pump startup or valve opening transient event where the flow through the GPV in the initial conditions is much lower, or even near-zero.
As a workaround, convert your GPV into an equivalent TCV (discharge coefficient or minor loss coefficient) or use the orifice-between-pipes element to model the flow vs. headloss relationship based on the pair of flow and headloss across your GPV as observed in another scenario where the initial conditions flow is close to what you expect after your pumps start up (or valve opens, for example). By doing this you can force the model to use a more appropriate discharge coefficient. This may change the initial conditions slightly, but enables you to model the desired headloss characteristics after the pumps start up or valves opens.
See Also
How can I model a backflow preventer?