Yorkshire Water
ABB
United Utilities
EPSRC
NEPTUNE MONITOR
CONTROL
OPTIMISE
AQUAI-MOD hydraulic controller Report Experimental and modelling studies
by Hossam AbdelMeguid, Piotr Skworcow, and Bogumil Ulanicki
11/2008 Process control - Water Software Systems, De Montfort University
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Table of Content Table of Content.................................................................................................................I List of figures ................................................................................................................... II List of tables....................................................................................................................III Local control for PRVs AQUAI MOD Hydraulic controller............................................1 Introduction....................................................................................................................1 Description of the AQUAI-MOD hydraulic controller .................................................2 Discussion of the test rig experiments hardware and software......................................5 Test rig........................................................................................................................5 Sensors........................................................................................................................5 Experiment procedure....................................................................................................8 Measuring capacitance of the modulation adjuster - procedure.................................8 Measuring capacitance of the of pilot valve - procedure ...........................................8 Measuring flow modulation characteristic - procedure..............................................9 Testing the dynamical properties of the controller - procedure .................................9 Experimental data of the PRV and AQUAI-MOD controller .....................................10 The mathematical model of the PRV and its controller...............................................15 Struggles to get solutions.............................................................................................25 Normal PRV – Steady state......................................................................................25 PRV and Controller – Steady state...........................................................................27 PRV and Controller – Dynamics..............................................................................27 Comparison of the Results of the Mathematical Model and Measurement Data ........28 Steady state results ...................................................................................................28 Dynamic and transient results ..................................................................................35 Conclusion ...................................................................................................................37 References....................................................................................................................38
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List of figures Figure 1. AQUAI-MOD controller ant its connection to PRV .........................................4 Figure 2. Schematic diagram of the test rig .....................................................................5 Figure 3. AQUAI-MOD hydraulic controller experiment layout ....................................7 Figure 4. Modulation curve of the AQUAI-MOD controller .........................................10 Figure 5. Effect of modulation adjuster opening on the maximum outlet head..............11 Figure 6. Effect of main pressure adjuster on the minimum outlet head ........................12 Figure 7. Dynamic effect of quick drop and rise in the main flow ................................13 Figure 8. PRV capacity ...................................................................................................18 Figure 9. Bi-Directional needle valve capacitance (flow out of the control space)........20 Figure 10. Bi-Directional needle valve capacitance (flow into the control space) .........20 Figure 11. Needle valve capacitance and saturation flow...............................................21 Figure 12. Flow modulation adjuster capacitance...........................................................22 Figure13. The solution of equation (15) for a given inlet head and flow. ......................27 Figure 14. Modulation adjuster effect – constant inlet head of 70 m .............................29 Figure 15. Modulation adjuster effect – inlet head varies according to pump characteristics..................................................................................................................29 Figure 16. The effect of main pressure adjuster - constant inlet head of 70 m...............30 Figure 17. The effect of main pressure adjuster - variable inlet head.............................31 Figure 18. Steady state
model results compared with experimental data for step
decreasing followed by step increasing of inlet flow, with 2.5 opening turns of modulation adjuster and 6.5 of main pressure adjuster...................................................32
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Figure 19. Steady state
model results compared with experimental data for step
decreasing followed by step increasing of inlet flow,
with 4 opening turns of
modulation adjuster and 6.5 of main pressure adjuster...................................................33 Figure 20. Steady state
model results compared with experimental data for step
decreasing followed by step increasing of inlet flow,
with 6 opening turns of
modulation adjuster and 6.5 of main pressure adjuster...................................................34 Figure 21. Steady state model results compared with experimental data of sharp closure and opening of downstream valve, with 3 opening turns of modulation adjuster and 6.5 of main pressure adjuster ................................................................................................35 Figure 22. Results of dynamic model compared with experimental data for step decreasing followed by step increasing of inlet flow,
with 3 opening turns of
modulation adjuster and 6.5 of main pressure adjuster...................................................36 Figure 23. Results of dynamic model compared with experimental data of sharp closure, with 3 opening turns of modulation adjuster and 6.5 of main pressure adjuster ............36
List of tables Table 1. Sensors specification...........................................................................................6 Table 2. Pipe material and dimensions ...........................................................................24
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Local control for PRVs AQUAI MOD Hydraulic controller
Introduction Water utilities use pressure control to reduce background leakage and the incidence of pipe bursts. Control is usually implemented across areas that are typically supplied through pressure reducing valves and closed at all other boundaries. Single-feed PRV schemes are often adopted for ease of control and monitoring but risk supply interruption in the event of failure. Multi-feed systems improve the security of supply but are more complex and incur the risk of PRV interaction leading to instability. A better understanding of the dynamics of PRVs and networks will lead to improve control strategies and reduce both instabilities and leakage. Dynamic models are currently available for representing behaviour of most water network components. Such models are relatively simple, accurate and can be easily solved. Prescott and Ulanicki (2003) developed the PRV dynamic phenomenological, behavioural, and linear models to represent dynamic and transient behaviours of PRVs. In anther hand, (Prescott and Ulanicki, 2008) developed a model to investigate the interaction between PRVs and water network transients. Transient pipe network models incorporating random demand were combined with a behavioural PRV model to demonstrate how the response of the system to changes in demand can produce large or persistent pressure variations, similar to those seen in practical experiments. In order to apply the optimal pressure control strategies, The AQUAI-MOD hydraulic controller is used to control the outlet pressure of the PRVs on utility potable water mains to provide water at the required head subject to consumer demand and to reduce this head when demand is not required. This will minimise continuous over pressurisation of the mains and therefore reduce energy consumption on pumps and stress on the mains causing potential leaks. The main purpose of this part is to describe a new experimental setup for testing the static and dynamic behaviour of the PRV and its AQUAI-MOD hydraulic controller experimentally, as well, to develop a mathematical model to describe the actual static
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and dynamic including transient behaviour of the PRV and its AQUAI-MOD hydraulic controller. And implemented this model to the hydraulic model of the water distribution net work to represent the dynamic effects of the PRV on the performance of the network, and to enhance the simulations and optimisation models of the WDSs.
Description of the AQUAI-MOD hydraulic controller As shown in Figure 1 the AQUAI-MOD hydraulic controller consists of three main chambers separated by rolling diaphragms. The first chamber is a Pitot chamber, which is connected to the Pitot tube at the downstream of the main valve (PRV). The second chamber is a control chamber, connected to the upstream, and control space of the PRV through a T-junction (t1). The pipe connected the valve inlet and T-junction, t1, have affixed orifice. The third one is a jet chamber, which is connected to the downstream of the PRV. The jet chamber is also connected to the Pitot tube through a T-junction (t2) before the Pitot chamber connection. As well, the control chamber is connected to the jet chamber through a hollow shaft, which allows the flow form control chamber to jet chamber through the discharge outlet of the jet. The resistance of the jet and the seat of the main adjuster depends on the gap between them, and work like a pilot valve. The major part of the valve is a hollow shaft with attached discharge jet and two pistons connected to the main body of the controller through rolling diaphragms. The space between the two pistons is called the control chamber and it has the constant volume. The control chamber is connected to the control space of the PRV and the upstream flow. Water enters the control chamber via the T-junction and leaves through the hole in the shaft. Subsequently it is conveyed to the discharge jet. The controller modulates the outlet pressure of the PRV according to the main flow, which is sensed and converted to dynamic pressure by a Pitot tube, which inserted into the downstream of the PRV and connected to the Pitot chamber of the controller. In response to the main flow during the operation of the controller, as the main flow increases the dynamic pressure increases, which yields to increase the force generated by the pressure difference in the Pitot chamber and the jet chamber, under the action of
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this force the main shaft of the controller moves to the right direction causes the gap between the outlet of the discharge jet and the main adjuster seat to increase, Subsequently, the pressure in the control chamber drops and water is taken from the control space of the PRV, the PRV is opening and the PRV outlet pressure increases. After the PRV outlet pressure increased the pressure in jet chamber increases, witch increase the force exerted on the secondary shaft. By the action of this force the secondary shaft moves to the right direction and the gab is decreasing again. Subsequently, the pressure in the control chamber rises and water is stop taken from the control space of the PRV and the PRV opening is maintained at the required position, and PRV outlet pressure is kept at the desired value. The controller has two setting points, the first one is the minimum pressure (corresponding to the minimum night flow), and this minimum pressure can be adjusted by main pressure adjuster by changing the initial tension of the spring and the gab. The working principle of this part is similar to that of a traditional pilot valve in a PRV (Prescott and Ulanicki, 2003). The second setting point is the maximum pressure (corresponding to the peak of demand), which can be set by the modulation adjuster (one directional flow needle valve), As the modulation adjuster is fully opened the PRV outlet pressure is flat without any modulation (standard behaviour of the PRV), by closing the modulation adjuster the maximum pressure is increasing and reach its maximum value by completely closing the modulation adjuster.
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Conclusion The AQUAI-Mod hydraulic controller is a new invented device to control and modulate the outlet head of the pressure reducing valve according to the flow. The controller is experimentally tested to assess its performance in different conditions and operating range. The controller in all cases show good performance as it modulates the outlet pressure as expected. It has two adjustment set points for the minimum and maximum head corresponding to the minimum and maximum flow, respectively. The outlet head is modulated between these two points. The mathematical model of the controller is developed and solved by Mathematica software package, in both steady state conditions and dynamics. The results of steady state mode are compared with the experimental data and it showed a good agreement in the magnitude and trends. And the steady state model can be used to simulate the behaviour of the PRV and the AQUAI-Mod hydraulic controller in most of network application, where the dynamics or transient are not taken into account. Also steady state model can be used to compute the required adjustment for the minimum and maximum head set points before installing the controller in the field. As well the full model of the PRV and the AQUAI-Mod hydraulic controller including dynamics and transient effect are solved and its results are showed a good agreement with the experimental data. In case of rapid decrease in the flow rate combined with rapid increase in the inlet head, the PRV is fully opened, and the outlet is the same as the inlet for a few seconds then the controller close the valve to the desired outlet head. It is obvious that, this case is not applicable for the normal operation of water distribution systems. In all other case of flow decreasing or increasing the outlet head is smoothly modulated to the desired values.
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References Brunone, B., and Morelli, L. (1999). "Automatic control valve–induced transients in operative pipe system." Journal of Hydraulic Engineering, 125(5), 534-542. Prescott, S.L., and Ulanicki, B. (2003). "Dynamic Modeling of Pressure Reducing Valves." Journal of Hydraulic Engineering, 129(10), 804-812. Prescott, S.L., and Ulanicki, B. (2008). "Improved control of pressure reducing valves in water distribution networks." Journal of Hydraulic Engineering, 134(1), 56-65. Ulanicki, B., Bounds, P.L.M., Rance, J.P., and Reynolds, L. (2000). "Open and closed loop pressure control for leakage reduction." Urban Water, 2 (2), 105-114. Ulanicki, B., AbdelMeguid, H., Bounds, P., and Patel, R. (2008). "Pressure control in district metering areas with boundary and internal pressure reducing valves." 10th International Water Distribution System Analysis conference, WDSA2008, 17-20 August, The Kruger National Park, South Africa.
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