Applies To Product(s): WaterGEMS, WaterCAD Version(s): 10.00.xx.xx, 08.11.xx.xx Area: Modeling Original Author: Scott Kampa, Bentley Technical Support Group Problem How can a user fix the WaterGEMS or WaterCAD error message " Network Unbalanced " or " Cannot solve network hydraulic equations ". A "Reverse flow detected" may be encountered as well. Background The "Network Unbalanced" and "Cannot solve network hydraulic equations" user notification means that the program could not converge on a balanced solution within the maximum number of trials. The difference between these is that the "Network unbalanced" message can occur for individual time steps, while the "Cannot solve network hydraulic equations" does not specify a time step where the issue occurs. Between calculation iterations, the program checks the relative change in flow, which has a default value of 0.001. If the relative flow change is below the "Accuracy" value designated in the calculation options, the time step is balanced or is said to have converged. If the relative flow change is greater than the Accuracy value, the program will try another iteration. If the program reaches the maximum number of trials without finding a solution, the "Network Unbalanced" user notification is generated. Solution Check Connectivity The first thing to do is to check to make sure your entire network is connected properly. Perform a validation (Analysis > Validate) on the model to see if there is information on possible issues in the model. If there are messages that are related to specific elements, double-click on it or right-click and choose "Zoom To", which will select the element in the drawing pane. Check the properties and setup of the element to see if there are issues related to data entry or orientation. If the element is a node, you can click and drag the element to make sure it is connected to all the pipes it is supposed to be connected to. Nodes that are not connected to pipes can occur if you used ModelBuilder to create the model. If your junctions are not connected properly you can use the Batch Pipe Split tool , which will allow you to connect the junctions to the pipes they are supposed to be connected to by splitting them. The Network Navigator tool can help you locate topological issues. (check the "See also" for two links on this) Check general model setup If there are not validation issues, make sure the setup of elements are accurate. Pay close attention to logical controls, valve settings, and valve status, empty or full tanks, and near zero flows as these are common causes of the issue. If you have a check valve on the pipe directly downstream of a pump, consider removing the check valve. In WaterGEMS and WaterCAD, a pump will not allow reverse flow. A check valve on the downstream pipe is redundant and can sometimes impact the model calculations. Check for zero or near-zero flows If you have a significant portion of your model with zero flow (such as the case when modeling "static" conditions), the numerical solver will have a hard time converging on a balanced solution. The reason is because the relative flow change between trials will typically be large in this case, since the numbers that it is dealing with are very close to zero. Check the link in the "See Also" section below for more on this. Other things to check If you have multiple fixed or variable speed pumps (VSP) discharging into the same pressure zone, this can also cause numerical instability. If the real system includes some manual operation of the pumps in this case, consider matching that in the model by using time based controls or a pattern (is variable speed pump = true, type = pattern). If you have GPV's check the "Flow Demanded" from the calculation summary (Analysis > Calculation Summary) at the time step of the red user notification. If the flow going to that GPV is not enough to provide the flow demanded examine the GPV headloss curve to make sure the maximum value of the curve is large enough to cover that flow. For example, if the flow demanded is 850 gpm check the largest value on the curve is at least 851 gpm. Confirm that tanks have the proper elevation data, including any top-fill tanks that may be in the model. If the model setup is accurate, you can find additional steps to help with this issue below. Intra-Trial Status Messages For EPS simulations you might find more clues to solving your problem by either: 1. (if you have V8i SELECTseries 5 or greater) - Click the time step in question in the Calculation Summary, then click the Intra-Trial details tab. This identifies elements that are changing status between trials 2. (if you have V8i SELECTseries 4 or earlier) - Open the .RPC file. This file contains a log of the trials that the program runs through when it is trying to converge on a solution. In order to open this file browse to the folder where your model is saved; that is where the .RPC file will be. You can open this file in a text editor, such as Notepad. Look down the trial list until you start to see the trials where there are elements that are constantly changing status (for valves a status change may be going from "active" to "closed" or vice versa and for pumps it could be going from "On" to "Off") over consecutive trials. The elements that have a constantly toggling status could be a clue to where your problem lies. If this happens often for certain elements then your model may be to tightly constrained or controlled and you should attempt to simplify the model where possible. If you are seeing many valves oscillating status in a particularly challenging timestep, this is an indication that their configuration should be checked, to ensure that they are correct and not accidentally "fighting against each other" due to the assumed settings. You might be able to adjust the configuration of those valves (in some cases with a conservative assumption) to make the model more simple and stable. In other words, try to address the root of the problem instead of tweaking the options to get it to work. This should be better in the long run if you can identify (with help from the intra-trial status messages) some changes that stabilize the model. For example this article talks about challenges like this that can occur with PRVs in parallel. Of course in some cases you may need to adjust the calculation options, in which case it does make sense to be extra cautious. Calculation Options Several advanced calculation options are available to help with convergence in challenging situations where the model data input and topology has been checked. First, you can try increasing the number of trials. To do this, go to Analysis > Calculation Options. Under the "Steady State/EPS Solver" section, double-click on the active calculation option to view the properties. Find the property field "Trials" and set this to a higher value, such as 400. In many instances, this is enough to allow the program to find a viable solution. Note that the program will not necessarily run all 400 trials, but will only use the number of trials it takes to come up with a viable solution. Other options to try changing 1. Engine Compatibility. The latest solver is "WaterGEMS 2.00.12". If you are using an older solver, using the latest may help as well. 2.. Convergence Check Frequency. This option sets the number of solution trials that pass during the hydraulic balancing before the status of pump, check vlaves, flow controls valves, and pipes connected to tanks are once again updated. 3. Convergence Check Cut Off. This option is the number of solution trials after which periodic status checks on pumps, check valves, flow control valves, and pipes connected to tanks are discontinued. 4. Dampening Limit. This is the accuracy valve at which solution dampening and status checks on PRVs and PSVs should begin. Change the value so that it is 10 times the accuracy. So if you have an accuracy of 0.001, set Damping Limit to 0.01. If that doesn't work, you can also try to increase the Accuracy field (also in Calculation Options properties) to a higher value, such as 0.01. This will mean that the relative flow change between iterations can be higher, which may allow the program to find a solution. You do not want the accuracy value to be too high though, or it may compromise the results. If you are using linear interpolation, you can try setting this to False, as shown in the screenshot below. This can help in cases where the pump is part of the issue. Note that these options are only available for the "WaterGEMS 2.00.12" solver. More information on these can be found at the following support solution: Engine Compatibility modes and Calculation Options . See Also "Network Unbalanced" problems with zero flow/ static conditions Engine Compatibility modes and Calculation Options Using The Network Navigator Using Network Navigator's Powerful Queries
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Wiki Page: Troubleshooting the Network Unbalanced or Cannot solve network hydraulic equations user notification
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Wiki Page: A free outfall in an Interconnected Pond Model reports 0 flow, but the upstream link has flow.
Product(s): PondPack Version(s): 08.11.01.56 Area: Output and Reporting Problem A free outfall in an Interconnected Pond Model (ICPM) reports 0 flow, but the link upstream of it has flow at the node and in the calculation summary Solution In ICPM models that have a mix of ICPM pond outlet links and free outfall links the free outfall links should be converted into ICPM links. If those ICPM links end at with a free outfall node set the outfall to the boundary condition type of "Time-Elevation Curve" and enter a time elevation curve as seen below. The elevation that is entered should be constant and be set below the bottom elevation of the upstream pond. Time Elevation 0.0 hours 10 ft. 12 hours 10 ft. 100 hours 10 ft. See Also Troubleshooting Mass balance and instability with Interconnected Pond Modeling (ICPM) User notification "Downstream TW out of range. Looking for TW value that is less than lowest table value."
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Wiki Page: Darwin Calibrator error "An error occurred when trying to calculate or validate the model..."
Product(s): WaterGEMS Version(s): 08.11.03.19 Area: Modeling Problem When running a calibration study, the following error message occurs: "An error occurred when trying to calculate or validate the model. Please check the model for errors" OR When computing Darwin Calibrator with customer meters associated with pipe elements the user notification "An error occurred when trying to calculate or validate the model. Please check the model for errors." is generated. Problem ID#: 84769 Solution This likely is related to an error or unexpected formatting in the data for the calibration study. Carefully review the data to make sure it is correct and the formatting is correct. For instance, if you have a pump setting in the Boundary Override tab that is negative, this will cause an error message. OR This is currently being worked on and will be fixed for an upcoming version of the software (# 710678). The workaround is to use the following steps to assign the customer meters to the nearest node element (junction, hydrant). 1) Open Loadbuilder and create a new Loadbuilder run 2) Choose the option at the bottom of the first window to where it states "Customer Meter load data" and choose the Nearest Node method located on the right side of the window. 3) Choose the node layer as a selection set the users have if they only want to assign the meters to certain nodes or choose "Junction/All Elements". 4) Choose the Customer Meter Layer "Customer Meter/All Elements" and keep the check box for exclude unconnected "Customer Meters that already have a valid Associated Element" unchecked. 5) Choose to update the existing alternative and select the alternative name. Add a Label to name the Loadbuilder run. See Also Using Darwin Calibrator
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Wiki Page: Applying a C adjustment factor to different return events
Applies To Product(s): PondPack, StormCAD, SewerGEMS, CivilStorm Version(s): 08.11.XX.XX, 10.00.00.XX Area: Modeling Original Author: Jesse Dringoli, Bentley Technical Support Group Problem My reviewer or locale requires an adjustment to be made to the C factor, which is different for each return frequency. How can I apply a different adjustment factor to the rational C for each return event? Solution Applying a C adjustment factor to catchment area for the PondPack To apply a different adjustment to the C factor for each return event, you can use the "C Adjustment" field in the properties of the modified rational catchment. Here are the complete steps: 1) Under Analysis > Alternatives, create a new Hydrology alternative for each return event. It is recommended that you label them according to the return frequency. If you only see the "Base Hydrology" parent alternative, you can use that to represent one of your return events and make child alternatives for the others. 2) Assign each of the Hydrology alternatives to the scenario representing the respective return event. 3) For each return event, make the respective scenario active, open the modified rational catchment properties and make sure "User defined" is selected for the "Outflow Criteria". 4) Enter the Target peak flow (allowable predevelopment outflow) for that return event and enter your adjustment factor in the "C Adjustment" field. The adjustment will be applied to the postdevelopment rational C coefficient(s). 5) Repeat step 4 for each return event. If you do not wish to enter the predevelopment target flow values but would rather enter them by way of the predevelopment C, area and Tc, choose "Predevelopment" as the "Outflow Criteria", then manually adjust the predevelopment and postdevelopment Rational C coefficients based on your factor. In either case, this information is stored in the Hydrology alternative, so the setting you choose will be kept separate when the scenarios are using different hydrology alternatives. Applying a C adjustment factor to the GVF Rational (StormCAD) solver The frequency factor has been added to the Rational Method to aid in the pairing of larger storm events with the Rational Method or Modified Rational Method, one option is to utilize the calculation options available for employing Frequency Factors. With the use of a Frequency Factor term the Rational Method effectively becomes: Q=C'iA Q = Rational Flow C' = Runoff Coefficient (Adjusted) i = Intensity A = Drainage Area C'=CfC Cf = Frequency Factor corresponding to the storm's Return Period (T) C = Runoff Coefficient (Unadjusted) You can enable use of frequency option through the calculation options.
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Wiki Page: What is the difference between the kinematic wave option and the dynamic wave option in the SWMM solver?
Applies To Product(s): Bentley SewerGEMS, Bentley CivilStorm Version(s): 08.11.XX.XX Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem What is the difference between the Kinematic Wave option and the dynamic wave option in the SWMM solver? Solution As noted in the EPA SWMM help documentation. Kinematic Wave Method: "This routing method solves the continuity equation along with a simplified form of the momentum equation in each conduit. The latter requires that the slope of the water surface equal the slope of the conduit. The maximum flow that can be conveyed through a conduit is the full normal flow value. Any flow in excess of this entering the inlet node is either lost from the system or can pond atop the inlet node and be re-introduced into the conduit as capacity becomes available. Kinematic wave routing allows flow and area to vary both spatially and temporally within a conduit. This can result in attenuated and delayed outflow hydrographs as inflow is routed through the channel. However this form of routing cannot account for backwater effects, entrance/exit losses, flow reversal, or pressurized flow, and is also restricted to dendritic network layouts. It can usually maintain numerical stability with moderately large time steps, on the order of 1 to 5 minutes. If the aforementioned effects are not expected to be significant then this alternative can be an accurate and efficient routing method, especially for long-term simulations." Dynamic Wave Routing "Dynamic Wave routing solves the complete one-dimensional Saint Venant flow equations and therefore produces the most theoretically accurate results. These equations consist of the continuity and momentum equations for conduits and a volume continuity equation at nodes. With this form of routing it is possible to represent pressurized flow when a closed conduit becomes full, such that flows can exceed the full normal flow value. Flooding occurs when the water depth at a node exceeds the maximum available depth, and the excess flow is either lost from the system or can pond atop the node and re-enter the drainage system. Dynamic wave routing can account for channel storage, backwater, entrance/exit losses, flow reversal, and pressurized flow. Because it couples together the solution for both water levels at nodes and flow in conduits it can be applied to any general network layout, even those containing multiple downstream diversions and loops. It is the method of choice for systems subjected to significant backwater effects due to downstream flow restrictions and with flow regulation via weirs and orifices. This generality comes at a price of having to use much smaller time steps, on the order of a minute or less (SWMM can automatically reduce the user-defined maximum time step as needed to maintain numerical stability)." Both of these entries are taken from EPA SWMM help documenation. You may also find more information by doing an internet search.
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Wiki Page: Opening a model file the error "Method requires triangulated DTM" is generated
Product(s): WaterGEMS, WaterCAD, SewerGEMS, SewerCAD, Civilstorm Version(s): 10.XX.XX.XX Area: Data Input Problem When opening a model file the error "Method requires triangulated DTM" appears, followed by "object reference not set...". Solution This could be due to a Terrain model (.TIN, .XML, .FIL, etc) that was previously attached but can no longer be found. For example it may have been moved or renamed. This issue will be addressed in a future release (reference defect 659454) If you are not sure where the file was originally located, you can change the path or remove it using this workaround: Workaround 1 - change or delete the DTM information from the .WTG or .STSW file 1) Open the .WTG file using a text editor like Notepad or WordPad and locate the section for the DTM by using the CTRL + F function. Type in "DTM" to locate the following section: through the line that ends with Within here you will see the file path and name of the DTM file. Either adjust it accordingly or remove the whole section noted above. 2) Save the .WTG file and close it. 3) Open the model file Workaround 2 - Import the file database Import the model file using the File > Import > Database or by selecting "database files" from the "files of type" dropdown in the file open dialog.
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Wiki Page: Flushing "An error occurred when trying to calculate or validate the model. Please check the model for errors."
Applies To Product(s): WaterCAD, WaterGEMS Version(s): 08.11.XX.XX Area: Output and Reporting Original Author: Alvidri Kurti, Bentley Technical Support Group Problem When trying to compute a flushing analysis, the following error occurs: "An error occurred when trying to calculate or validate the model. Please check the model for errors." The model contains a variable speed pump whose control node is included in the flushing analysis. Problem ID#: 36544 Internal Reference Number: P51844 Solution This often occurs if there is a fixed head variable speed pump in the system and the target head node is included in the flushing analyses. The reason why this causes a conflict is because during the flushing analysis the target node is changed into a flow emitter. In order to fix this issue, place an extra node in the system, next to the target node, assigning the same elevation as the target node. Now you can use this newly created node as the target node and include the existing node in the flushing analysis.
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Wiki Page: I'm trying to search for an element label, but WaterCAD brings up an element with the same ID
Applies To Product(s): WaterCAD, WaterGEMS, SewerGEMS, CivilStorm, StormCAD, PondPack, SewerCAD, HAMMER, Version(s): 08.11.XX.XX, 10.XX.XX.XX Area: Output and Reporting Original Author: Alvidri Kurti, Bentley Technical Support Group Problem I'm trying to search for an element label, but WaterCAD brings up an element with the same ID. Problem ID#: 38678, GENERALINFORMATION Solution WaterCAD allows the same labels to be used for multiple elements, but each element has a unique ID. Whenever searching for an element label that is used twice WaterCAD skips to search for the element ID. Open the element flextable and locate the label you would like then right click on the row column header and choose Zoom to element to identify the correct element.
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Product release date (estimated) - Storm, Sewer
Estimated release date for Storm and Sewer CONNECT Edition update 1: End of September, 2017. Subject to change. This applies to the following products: StormCAD SewerCAD SewerGEMS CivilStorm How can I find out when a new version or patch is released for a Hydraulics and Hydrology product?
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Product release (estimated) - Water
Estimated release date for Water CONNECT Edition update 1: End of November, 2017. Subject to change. This applies to the following products: WaterGEMS WaterCAD HAMMER How can I find out when a new version or patch is released for a Hydraulics and Hydrology product?
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Forum Post: 'StormCAD for UK' 'country kit'
Hi, I have installed the Strom Cad V8i , I would like know if can install UK Country kit. if so Kindly help me with download link, I am looking the Bentley download its not showing in the list. Thanks, Digvij
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Wiki Page: What does the following user notification mean: "Cross Section dimensions are ignored. Conduit attributes are used instead."
Product(s): Bentley StormCAD, CivilStrom, SewerGEMS Version(s): 08.11.XX.XX Area: Layout and Data Input Problem What does the following user notification mean? "Cross Section dimensions are ignored. Conduit attributes are used instead." Solution This will occur if there is a Cross section node at both ends of a conduit. The reason is the cross sectional area of a conduit is assumed to be constant over its length, whereas the cross sectional area of a channel is defined at the end points, which need to be Cross Section nodes. In other words, the message is there to inform you that the cross section of the conduit is defined by the conduit itself, not by the Cross Section nodes at the ends, which is generally the case for channels. In most cases, a series of conduits would have junction chambers, catch basins, or manhole nodes at the endpoints. Cross section nodes would only be used if at least one channel link element is attached. In some cases, it may be possible that a series of conduits have cross section nodes at the endpoints through importing of a certain file format for example. So, this message is here to alert you that the cross sectional area that you defined in those nodes are ignored, because the geometry of the conduits is defined in the conduit itself. See Also
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Wiki Page: Pump station results when running hydraulic analysis
Product(s): Bentley WaterGEMS, WaterCAD Version(s): 08.11.XX.XX Area: Output & Results Problem Is there a way to get results for a pump station element when just running a hydraulic analysis? All I see is results for an Energy Analysis. Problem ID#: 69834 Solution The results seen within the properties of the pump station are the only available results. Although many of these results are energy cost related, there are some that may be considered "hydraulic". For instance, the "Flow (total)" will show the total flow through the entire pump station for each time step, and the "Volume Pumped (cumulative)" will show the cumulative volume of water that has passed through the entire pump station. To view these results, you will need to compute an energy cost simulation, under Analysis > Energy Costs. You can still compute energy cost without entering any pricing information. Of course, the other main purpose of the pump station element is to accommodate the Combination Pump Curve tool, which can be accessed from right clicking the pump station. Beyond that, you would need to look at the properties of each individual pump to see for example the pump head, flow, relative speed factor, etc. See Also
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Wiki Page: The version of the model file you are importing is no longer supported
Product(s): Bentley SewerGEMS Version(s): 08.11.02.46 Area: Data Input and Modeling Problem Why do I get the following message when trying to import my SewerCAD model in SewerGEMS? "The version of the model file you are importing is no longer supported. It was either created with an older version of the product or is a file from a different product." Problem ID#: 49384 Solution This means that the model is saved in an earlier version of SewerCAD. In order to open it in SewerGEMS, you'll need to first save it in a newer version of SewerCAD. The easiest way to do this is to open the file in SewerGEMS Sanitary, which is included with SewerGEMS V8i. SewerGEMS Sanitary is essentially the same product as SewerCAD, but will have the same version as your SewerGEMS. You can find the shortcut to open SewerGEMS Sanitary on your desktop or start menu folder. So, open the SewerCAD model in SewerGEMS Sanitary, save it, then you'll be able to import it in SewerGEMS. Starting from SS2 version of SewerGEMS Sanitary is no longer a separate version. See Also
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Wiki Page: Velocity Filter is restricting Velocity and changing value for specific headloss.
Applies To Product(s): SewerGEMS, CivilStorm Version(s): 08.11.XX.XX Area: Calculations Original Author: Dan Iannicelli, Bentley Technical Support Group Problem Why is there a velocity filter restricting velocity and changing the value for specific headloss? #76876 Solution The velocity filter is an attribute that reduces velocity when using the Standard Loss Method. For numerical stability reasons an empiric velocity filter is used when the velocity is larger than 5.0 ft/s as follows: v = 5.0 + 0.1*(v1 -5.0) in which v is the velocity applied to the head loss equation and v1 is the original velocity
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Wiki Page: "Results Not Saved" computing a model in version 5.6
Applies To Product(s): StormCAD, SewerCAD Version(s): 5.6 Area: Calculations Original Author: Bentley Technical Support Group Problem Results Not Saved - Warning--Results Not Saved Error when Pressing GO Solution The error is due to insufficient RAM. Result files (.out) are saved only if there is some enough memory (RAM) on computer 1) Close other open programs such as AutoCAD or Microstation. 2) Close the program, delete the output files (.out, .rst and .rpc, with the same base file name of your model) and reopen the model 3) Reboot your computer and Open/Run your StormCAD model before opening any other programs 4) Allow the program to access extended memory by following these steps: -Make sure the program is closed. -Make sure your computer has at least 1GB of RAM -Using windows explorer, browse to the software's program directory. The default should be C:\Program Files\Bentley\StormCAD\ -Be sure that you have file extensions turned on. You can turn them on by going to Tools > folder options > View and make sure that "hide extensions for known file types" is unchecked. -Rename the STMCsys.exe file to something similar to STMCsys_bak.exe -Make a copy of the v10a.exe file and paste it into a different folder (such as the "samples" folder) -Rename this file to "STMCsys.exe" and move it back to the main program directory (StormCAD). -Open the program - you should now be able to utilize the full 1GB of memory. -If you get an error about being out of address space, please follow these steps again, using "v10.exe" instead of "v10a.exe"
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Forum Post: How to design interconnected (via culverts) balancing ponds (without any real outfall) in CIVIL STORM????
i am working on a project where i have to design some ponds in the intersections of roads. These ponds should be interconnected via culverts and these ponds will store water which will ultimately be evaporated. This system will not be having any outfall as we dont have any structure where we can discharge the flow
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Wiki Page: What does it mean when an FCV is set to a status(initial) or 0?
Applies To Product(s): WaterCAD, WaterGEMS Version(s): 08.11.XX.XX, 10.XX.XX.XX Area: Output and Reporting Original Author: Mark Pachlhofer, Bentley Technical Support Group Problem What does it mean when an FCV is set to a status(initial) of 0 (zero)? Problem ID#: 82720 Solution A setting of zero for an FCV will limit the flow to zero, which essentially means that the valve is closed. Note that if you have demands downstream of the FCV with no other path for them to be satisfied, you can encounter problems, as explained here: How do I model a system where there is intermittent demand or where demand is being cut off from it's water source at some point? Ill-conditioning User Notification for valves in a hydraulic model
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Wiki Page: How does the Pressure Reducing Valve (PRV) work?
Applies To Product(s): WaterGEMS, HAMMER, WaterCAD Version(s): 08.11.XX.XX Area: Modeling Original Author: Jesse Dringoli and Mark Pachlhofer, Bentley Technical Support Group Problem How does the Pressure Reducing Valve (PRV) work? Solution Definition Pressure reducing valves (PRVs) throttle (ie. restrict) flow to prevent the downstream pressure or hydraulic grade from exceeding a user-defined value. PRV Effects on the System The upstream hydraulic grade and pressure increase. The downstream hydraulic grade and pressure decrease. Practical Applications To separate pressure zone boundaries in water distribution networks. To avoid downstream pressures that could have damaging effects on the system (eg. burst pipes, cause relief valves to open). Steps to Create Select PRV from the layout toolbar. Place it in the network. Define the PRV's attributes. Note: For a complete list of the PRV attributes explained in detail, see the help article "Pressure Reducing Valve (PRV) Attributes". A couple of notes for PRV attributes are included below. Valve "Status (Initial)": Active: Valve is partially opened to limit the user-defined downstream pressure or hydraulic grade. Inactive: Valve is fully open. Closed Minor Loss Coefficient: A PRV's minor loss coefficient is only a concern when the valve is not throttling flow (ie. wide open). This is because the PRV introduces loss to meet a required downstream hydraulic grade or pressure. Reverse flow through the PRV Reverse flow through a PRV is allowed when the "Status (initial)" is set to Inactive. When the PRV's "Status (initial)" is set to Active, reverse flow is not allowed and "Status (Calculated)" will be set to Closed. Example First, check how the system behaves without the PRV by setting the PRV's attribute "Status (Initial)" to Inactive (ie. fully open) and then computing the model: Downstream Pressure = 90psi Downstream Hydraulic Grade = 260ft Next, check how the system behaves when the PRV is completely closed by setting "Status (Initial)" to Closed and then computing the model: Downstream Pressure = 35psi Downstream Hydraulic Grade = 130ft Therefore, the PRV can control the downstream pressure to be between 35-90psi, or control the hydraulic grade to be between 130-260ft. Now, switch "Status (Initial)" to Active to let the PRV's initial settings determine the valve status. The scenarios below give an idea of when the PRV's calculated status would be inactive, active and closed. For: "Setting Type" = Pressure Pressure Setting (Initial) Status (Calculated) 0psi Closed (1) 60psi Active (2) 100psi Inactive (3) (1) If the PRV's downstream pressure can't be lowered to the value defined for the "Pressure Setting (Initial)", then the "Status (Calculated)" is set to Closed to provide the minimum downstream pressure. (2) If the PRV's "Pressure Setting (Initial)" is below the downstream pressure when "Status (Initial)" is set to Inactive, and throttling the PRV will allow the "Pressure Setting (Initial)" to be maintained, then "Status (Calculated)" is set to Active (ie. partially open). (3) If the PRV's "Pressure Setting (Initial)" is above the downstream pressure when "Status (initial)" is set to inactive, then the "Status (Calculated)" is set to Inactive (ie. fully open) as there is no throttling necessary. This is because even with the PRV fully open, the downstream pressure is already lower than required and any throttling would just decrease the pressure more. Similarly, for: "Setting Type" = Hydraulic grade Hydraulic Grade Setting (Initial) Status (Calculated) 125ft Closed (4) 190ft Active (5) 265ft Inactive (6) (4) If the PRV's downstream hydraulic grade can't be lowered to the value defined for "Hydraulic Grade Setting (Initial)", then the "Status (Calculated)" is set to Closed to provide the minimum downstream hydraulic grade. (5) If the PRV's "hydraulic Grade Setting (Initial)" is below the downstream hydraulic grade when "Status (Initial)" is set to Inactive, and throttling the PRV will allow the "Hydraulic Grade Setting (Initial)" to be maintained, then "Status (Calculated)" is set to Active (ie. partially open). (6) If the PRV's "Hydraulic Grade Setting (Initial)" is above the downstream hydraulic grade when "Status (Initial)" is set to inactive, then the "Status (Calculated)" is set to Inactive (ie. fully open) as there is no throttling necessary. This is because even with the PRV fully open, the downstream hydraulic grade is already lower than required and any throttling would just decrease the hydraulic grade more. How is the headloss across the PRV determined? The headloss across the PRV is calculated based on the difference between the upstream and downstream HGL's. The upstream and downstream HGL's are determined from the boundary conditions of the model, which include tank, reservoir, or valve hydraulic grades. How does the PRV operate during a transient simulation in HAMMER? During a transient simulation in HAMMER, by default, PRVs are assumed to operate at a fixed position based on the initial conditions, unless the modulation option is used. See: Using Modulating PRVs See Also How does the Pressure Sustaining Valve (PSV) work?
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Forum Post: RE: How to design interconnected (via culverts) balancing ponds (without any real outfall) in CIVIL STORM????
Thanks alot Scott..... i was doing my model with the second option you have given but i was missing the outfall in the last pond... you have resolved my problem .... Cheers
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