Control Valve vs. Regulators for Gas Pressure Reduction? – How to Decide
November 27, 2018 Welcome
Pressure regulators and pressure relief or control valves are important instruments in the oil and gas industry used for the same purpose – automated fluid control. However, the two instruments differ fundamentally in operation and design.
It is important for operators, engineers, and other relevant stakeholders to understand the differences between these devices in order to determine the most suitable choice for various applications.
So, for Control Valve vs. Regulators: How do you decide which is right for you?
To get a clearer picture about how both devices work, it’s important to first understand the basics of a process control loop.
The Control Loop System
A control loop is a system designed to apply or restrict a measured process variable based on its degree of deviation from a predetermined set point. Controlled process variables can be anything from temperature to pressure, volume, level etc.
How It Works
In a typical control loop, a process variable is first detected and measured by a sensor which transmits information concerning its value to a host or Distributed Control System (DCS). The DCS then interprets the information in relation to a predetermined set point value designed to allow or restrict that process and relays a signal to an actuator about the degree to which it must open or close to return the process to the original set point.
Process Control in Oil & Gas
In the downstream oil and gas industry, a control loop system is used to allow or restrict the flow of hydrocarbons through a system based on predetermined set point values. These might be used in LACT Skids or for oil surge system management.
There are various types of equipment used for flow control are:
- Pressure control valve (PCV)
- Pressure relief valve (PRV)
- Pressure regulator
- Flow control valve
Pressure Control Valve
A pressure relief valve or pressure control valve (PCV) determines the degree to which a valve opens or closes in response to an electrical signal generated from one or more process variables. Pressure control valves are based on the standard control loop system. A good example is a PCV used to control fluid pressure through a pipeline.
A pressure regulator is a device designed to allow or restrict the flow of process fluids through a channel by applying the process fluid to the surface of a diaphragm. The fluid will either be allowed or prevented from flowing based on the set point pressure.
Difference Between Pressure Regulator and Pressure Control Valve
A pressure control valve controls fluid flow by opening or closing a valve based on an electrical signal generated from a process variable (e.g. temperature, pressure, level etc.), a regulator is controlled directly by the process.
For instance, a pressure regulator does not require an external source of power to function i.e. pressure from the fluid on the diaphragm is what activates the open/close action of the valves.
The PCV will open an outlet valve to permit hydrocarbons only is its pressure is equal to or slightly below the set point pressure to which the pipeline is rated. Automating fluid control in this way is quite beneficial for maintaining a safe transport pressure as well as accurate metering of the commodity.
Difference Between a Pressure Control Valve and a Pressure Relief Valve
A pressure relief valve (PRV) and a Pressure control valve (PCV) are both used for pressure control purposes but differ in operation.
A PCV serves as the primary line of defense in an oil field which prevents overpressurized flow line of hydrocarbons through a channel. A PRV is a static secondary safety device used to ‘bleed off’ excess pressure from an oil and gas well or pressurized system.
Pressure Regulator vs. Pressure Relief Valve
A Pressure regulator differs from a PRV in a few ways. Like a PCV, a Pressure regulator is a primary safety device used for pressure control in oil and gas facilities. On the other hand, a PRV is secondary safety device used for secondary (non-critical) pressure control.
Pressure Safety Valve (PSV)
A pressure safety valve or PSV is an automatic safety device used to immediately relieve pressure on a compressible fluid vessel to avoid critical failure and loss of life due to overpressurized vessel conditions.
Difference Between PCV and PSV
A PSV is closely related in function to a PCV. The main difference between PSV and PCV is that a PSV’s valves open almost fully immediately a fluid achieves set point temperature unlike the PCV which opens up gradually.
Choosing the Right Control Instrument – Speed of Response
Since they are process-controlled and do not require an intermediate relay system for control, pressure regulators generally have a faster response time than pressure control valves.
PCVs need to rely on continuity between DCS, sensors, and actuators. Thus, the entire system is subject to instrumentation failure when one component is defective.
High-precision Custody Transfer with Integrated Flow Solutions
The experts at Integrated Flow Solutions (IFS) are oil and gas skid manufacturers that design and produce configured-to-order liquid measurement systems and engineered-to-order pumping and process systems optimized for all key players across the energy industry value chain. Contact us today for information about how we can improve your process systems with our high-efficiency skids.