PATs Operating in Water Networks under Unsteady Flow Conditions: Control Valve Manoeuvre and Overspeed Effect
Abstract
:1. Introduction
2. Material and Methods
2.1. Basic Hydraulic Modelling of the Transient Conditions
- The flow is homogenous and compressible;
- The changes of density and temperature in the fluid are considered negligible when these are compared to pressure and flow variations;
- The velocity profile is considered pseudo-uniform in each section, assuming the values of momentum and Coriolis coefficients constant are equal to one;
- The behaviour of the pipe material is considered linear elastic;
- Head-losses are calculated by uniform flow friction formula, which is used in steady flow.
2.2. Control Valves
2.3. Damping Effects
2.4. Runaway Conditions
3. Results and Discussion
3.1. Experiments and Simulations
3.2. Control Valve Closure and PAT Trip-Off
3.3. Control Valve Opening and PAT Start-Up
3.4. Overspeed Effect in PATs
4. Conclusions
- the characteristics of the pipe system to be protected; in fact, these characteristics based on the head loss and inertia of the water column can adversely modify the system behaviour and the same valve closure time can induce a slow or a rapid flow change;
- the intrinsic characteristics of the valve: a butterfly valve (e.g., for medium heads) and a spherical valve (e.g., for high heads) have different effects on the dynamic flow response for the same closure law;
- since PATs have no guide vane, the flow control is made through valves where the closure and opening laws are crucial in the safety system conditions, such as the type of the valve actuator;
- based on the characteristics of the pump such as turbine machine (i.e., radial or axial), different dynamic behaviour will be associated with:
- ○
- the small inertia of the rotating masses induces a fast overspeed effect under runaway conditions imposed by a full load rejection.
- ○
- the overspeed effects provoke flow variations (i.e., flow reduction in low ns machines and flow increasing in the high ns machines) and pressure variations that can propagate upsurges upstream of a radial machine and downsurges downstream of it, in contrast to axial machines (downsurges upstream and upsurges downstream).
Author Contributions
Funding
Conflicts of Interest
References
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Material | Inner Diameter (m) | Roughness (mm) | Wave Speed (m/s) |
---|---|---|---|
HDPE | 0.044 | 0.2 | 280 |
PVC | 0.110 | 1.2 | 385 |
Rigid PVC | 0.047 | 0.2 | 527 |
Steel | 0.068 | 2 | 1345 |
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Pérez-Sánchez, M.; López-Jiménez, P.A.; Ramos, H.M. PATs Operating in Water Networks under Unsteady Flow Conditions: Control Valve Manoeuvre and Overspeed Effect. Water 2018, 10, 529. https://doi.org/10.3390/w10040529
Pérez-Sánchez M, López-Jiménez PA, Ramos HM. PATs Operating in Water Networks under Unsteady Flow Conditions: Control Valve Manoeuvre and Overspeed Effect. Water. 2018; 10(4):529. https://doi.org/10.3390/w10040529
Chicago/Turabian StylePérez-Sánchez, Modesto, P. Amparo López-Jiménez, and Helena M. Ramos. 2018. "PATs Operating in Water Networks under Unsteady Flow Conditions: Control Valve Manoeuvre and Overspeed Effect" Water 10, no. 4: 529. https://doi.org/10.3390/w10040529