Headloss through Flow control Valve

Hello Martin,

The Flow Control Valve (FCV) requires the "Flow Setting (Initial)" i.e. the initial flow setting of the valve.

What parameters are you using for the FCV? What is the flow you wish to control?

In the FCV properties you have the option of specifying user defined minor loss or discharge coefficient.

Are you getting an any error using the FCV? If so please share a screenshot of the same.

Here is a reference article on modeling valves;

Modeling Reference - Valves

Hope this helps

Hi,

I'm using Flow control Valve to limit the flow downstream of the valve. 

Flow Setting (Initial) is my desired downstream flow which I'm feeding in the model. Problem is the headloss through the valve after the analysis which is 53.88 after analysis (highlighted in below figure) whereas as per valve manufacturer, it shall only be 4 metres. There is no place to specify the headloss through the valve. Changing the minor loss coefficient does not change the Headloss through the valve.

Exactly what kind of valve is this an dhow is it being controlled? Is this a true FCV which has a flow meter which provides flow rate to a PLC which determines the valve position? Or are you using the FCV element to trick the model into giving you a certain flow downstream?

A real flow control valve will throttle the flow (by increasing head loss) until the desired flow is achieved. The claim  of 4 m head loss usually refers to a certain flow rate.

Hi

This is a Flow Control Valve with an orifice Plate and is Pilot Controlled which maintains a constant pressure differential through the orifice plate to achieve a constant downstream flow irrespective of upstream flow till the time the upstream flow is greater than or equal to downstream flow. And the headloss through the valve shall always remain 4 m as specified by valve manufacturer. But problem is that Hammer does not have option to fix the headlines through a FCV element. How to achieve this ?

Hi

This is a Flow Control Valve with an orifice Plate and is Pilot Controlled which maintains a constant pressure differential through the orifice plate to achieve a constant downstream flow irrespective of upstream flow till the time the upstream flow is greater than or equal to downstream flow. And the headloss through the valve shall always remain 4 m as specified by valve manufacturer. But problem is that Hammer does not have option to fix the headlines through a FCV element. How to achieve this ?

As explained, a FCV will dynamically throttle and induce the headloss necessary to maintain the target flow, based on energy balance across the rest of the model. This is explained here: Why do I see such a large headloss through my FCV, PSV or PRV?

Basically the headloss you see is the amount that would be necessary to achieve the desired flow, based on the upstream and downstream boundary conditions, assumed demands, etc.

If you need to model a valve that throttles to induce a specific headloss of 4 m, that is done using the Pressure Breaker Valve (PBV). However, if the FCV approach predicts that the headloss would be greater than 4 m, it means that the flow through the PBV (set to 4 m of loss) would be greater than the desired flow, based on the hydraulics of the system. You may also need to look at the assumed demands and boundary conditions in your model.

You mentioned HAMMER, though. During a transient simulation, HAMMER does not have enough information to know how quickly such a valve would react, so it assumes that all valves are in a fixed position during the transient simulation, unless an Operating Rule is supplied. Read more about that here.

Dear Jesse

What you have explained is understood but my valve manufacturer is confident that for reduced flow through the flow control valve, the headloss shall not be 53.88 m (as shown by HAMMER) but 4m. How to change that in HAMMER ?

Hello Martin, 

There are multiple factors as mentioned by other colleagues, which will cause the headloss like upstream and downstream boundary conditions, assumed demands, headloss due to small pipes etc.

You need to go through all the inputs to make sure they are correct and identify reason behind this headloss. 

Please at the wiki link provided by Jesse, in his reply, which might explain the reason for your model. 

If you are in modeling stage of the water supply network and not doing transient analysis, you should be using WaterGEMS / WaerCAD for that, not Hammer. 

If required you can upload the model files for our review. 

Sharing model files 

If you were to force the 53.88 m headloss to be 4 instead, then energy would not balance across the model, for the same flow and assumed boundary conditions. As Sushma mentioned, you will need to see what might be different between your model and the conditions in the real system that would cause there to be exact 4 meters of headloss at exactly the desired flow.

Try using a PBV with the head drop set to 4 m, and adjust other model parameters until the flow reaches the desired rate.