FCV closure

Question

Dear Jessi: 
 This case without using the PRV upstream the FCV valve: 
 Kindly, I have a model a gravity system controlled by a FCV that restrict the flow up to 1141.6m^3/hr where the pipeline is DN700 Ductile and of length 33.5 km. I follow all the steps to modify the FCV to TCV. As a result, The Cv initial = 0.81278m^3/sec/mH2O^0.5 based on hl = 57.86 m and the Cv at full open = 67.76146 m^3/sec/mH2O^0.5 based on inactive initial condition for the FCV and a minor loss coefficient =0.24 (this value for butterfly valves for 5dgree from manufacturer). in this way the TCV works as FCV for maximum flow = 1141.6m^3/hr 
 
 The next step: 
 I proposed an operating rule as shown in the following figure below.

I select the butterfly as a Valve type , and after reviewing the curve of the valve closure % and Cv %; I want to the initial closure to be 5%. As for the curve of the selected valve type, the Cv% will be 91% closure, accordingly, the calculated initial Cv = 0.91*67.76146 = 61.66293m^3/sec/mH2O^0.5 to be inserted as initial CV:

After computing initial condition, no problem shown about the closure I have selected, but since the CV initial value is changed to new value 61.66293m^3/sec/mH2O^0.5; the TCV as a FCV didn't control the flow up to 1141.6m^3/hr it leave the system to a larger flow 1,802.357m^3/hr as in the original system without FCV and the Compute Tool didn't work for surge. Please advice. 
 
 Some other questions: 
 -is there is a preferable operating rule ranges for FCV or as the designer believe? 
 - is the minor loss coefficient i selected acceptable for full open 0.24? 
 
 The following represent the results if i build the model without PRV: 
 Kindly, I have a model to a FCV to restrict the flow up to 1141.6m^3/hr where the pipe line is DN700 DI and of length 33.5 km. I follow all the steps to modify the FCV to TCV. As a result, The Cv initial = 0.08274 m^3/sec/mH2O^0.5 based on hl = 14.68m and the Cv at full open = 3.47495 m^3/sec/mH2O^0.5 based on inactive initial condition for the FCV and a minor loss coefficient =0.24. Note that there is a PRV just upstream the FCV just to reduce the pressure up to 2 bars as per requirement of the design). 
 The next step : 
 I proposed an operating rule as shown previously.

I select the butterfly as a Valve type , and after reviewing the curve of the valve closure % and Cv %; I want to the initial closure to be 5%. As for the curve of the selected valve type, the Cv% will be 91% closure, accordingly, the calculated initial Cv = 0.91*3.47495 = 3.162 m^3/sec/mH2O^0.5 to be inserted as initial CV:

After computing initial condition, no problem shown about the closure I have selected, but since the CV initial value is changed to new value; the TCV as a FCV didn't control the flow up to 1141.6m^3/hr it leave the system to a larger flow 1,802.357m^3/hr as in the original system without FCV and the Compute Tool didn't work for surge. Please advice.

Scott Kampa · Accepted Answer

Hello Sawsan, 
 
You are using an older version of HAMMER. If you have a Select contract with Bentley, I would recommend upgrading. 
 
The first thing you should do is watch the units you are using. It appears that some of your discharge coefficients are using US units instead of metric. This will obviously have an impact on the results. I would simply be consistent, making sure to us metric units if the rest of the model is metric. 
 
The following steps would be the recommended workflow for this sort of analysis. Starting with the model with the FCV in the model, you would get the discharge coefficient and relative closure results for when the FCV is active and when it is inactive. This will be used for the TCV you will be modeling. The values below will be for the case without the PRV upstream of FCV. The steps will be similar for the case with the PRV in the model. 
 
First, you will compute the model with the FCV active and with a setting of 1141.6 m^3/hr and a minor loss coefficient of 0.24. After computer, the resulting discharge coefficient is 0.04166 m^3/s/(m H2O)^0.5. Please note also that the relative closure is 89.5%. Next, change the initial status of the FCV to Inactive and compute the model again. In this case, the discharge coefficient is 3.47878 m^3/s/(m H2O)^0.5 (the relative closure is 0%, as expected). These are the values that you will be using when you change the FCV into a TCV. 
 
Now, in the model with the TCV, you will enter the values found above for the TCV discharge coefficient values. The fully open discharge coefficent for the TCV will be set to 3.47878 m^3/s/(m H2O)^0.5. The initial discharge coefficient will be set to 0.04166 m^3/s/(m H2O)^0.5. With those settings, the calculated flow through the TCV about 1141.6 m^3/hr. 
 
However, the relative closure for this case is 89.5%. You state in your email that you want a relative closure of 5%, however this will not correspond to the flow that you want. If you need the flow to match the flow from the FCV, you will need to use the larger relative closure for the start of the operating rule. 
 
So you know, the basic information for the steps above can also be found at the following link: communities.bentley.com/.../6905.modeling-existing-valves-as-throttle-control-valves-in-hammer 
 
As for your question on the operating rule, the operating rule used will be up to your engineering judgment. The operating rule basically defines how quickly the valve will close. If you wanted a conservative result, you may want to have a relatively fast closure time. However, if you have general information for how the valve will close based on field results or valve operation, you should use that information. 
 
Regarding your question on the minor loss, you may need to check an engineering reference to see if you have information on minor losses for the valve you are using. In HAMMER's engineering library (Components > Engineering Libraries) there is a minor loss library. Butterfly valves are not listed among the available minor losses though. Your valve manufacturer may have the information you need for this. 
 
Regards, 
Scott