Emerson Exchange 365

One common misconception about pressure regulators is that they only control pressure immediately upstream or downstream of the valve. However, most pilot-operated regulators and some self-operated regulators operate using an external control or sensing line. This line can be used to control pressure at a remote location in the process pipeline, and there are a variety of reasons for doing so.

Some reasons for using an external control line include:

-          Wanting to control pressure more accurately at a specific location in the process upstream or downstream from the regulator

-          Lack of space which might require a remote regulator installation

-          Regulator monitor setups that  require an external control line

Whatever the reason for using an external control line, it is important to remember that the control line is the nervous system of the regulator. One common cause of system pressure control issues is incorrect installation of control lines. Some things to keep in mind when using control lines are:

1. When using a control line, keep the line as short and straight as is feasibly possible.  The shorter the sensing line the quicker the regulator can sense and respond to changes in system pressure.
2. Minimize any elbows, tees, valves and other friction and restriction causing devices in the control line.  When using isolation valves remember to use full port valves
3. The control line should be connected 6 to 10 pipe diameters downstream of any turbulence generators (e.g. valves, swages, elbows)
4. The pressure is being controlled exactly at the point where the control line is tied into the main line and not at the regulator, so design pressure of the regulator and equipment prior to the sensing lines should be reviewed to ensure they meet process safety requirements
5. Control line diameter should start at the connection size provided on the regulator. As the control line length increases, so too should the size of the control line. A good rule of thumb is to increase control line size every 10-15 feet of run

The above tips are just general guidelines, and as every application is different customers may find themselves unable to follow them to the letter. If you have questions about control line installations or best practice recommendations, please feel free to comment.