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Changing Pressure control loop to Flow control loop while the valve originally designed for Pressure control

Hi,

One of the operational requirement is to change the Pressure control loop to Flow control loop.

All setup are available like below:

1. Pressure & flow transmitter are available.

2. Loop change in control system can be done easily.

The question is "The design of the control valve is for pressure control", now will it perform properly in "Flow control loop" ? What are the factors should be taken care?

I will communicate with local Emerson design team to get their concurrence, but before that, want to have general opinion. The process medium is Gas.

Goms

• 22 Oct 2020 7:21 AM
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1 Reply

• Jeffrey Mach

  

  • 27 Oct 2020 1:34 AM

  I think the folks at Emerson are going to ask for more information on what you mean by: "The design of the control valve is for pressure control". They will want to know what kind of valve it is and any information you could share about the valve characteristic data and actuator. For example: If you have a dome-loaded pressure regulator, then maybe it will be difficult to use it as a flow regulator. That said, if you have the gas flowing through a downstream orifice where you can maintain sonic flow across your normal operating range, then a pressure regulator becomes a flow regulator.
  
  Different types of valves are better or worse at controlling flow. So whether you can use the existing valve will also strongly come down to your process. How variable is are the inlet and outlet conditions (pressure, flow rate)? What is your allowable output variance / accuracy? If you have a relatively slow and steady process, and your allowable accuracy is loose, you may be able to make just about any analog valve work for you. On the other hand, it may not be reasonable to attempt to have your current valve do the job, and you will need to replace it with one better suited for the job.

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