Back Pressure Valves vs.
Back Pressure Regulators
A Back pressure valve provides a similar function to a back pressure regulator, though the feedback mechanism is typically different. This article compares and contrasts the function and performance of each.
For applications up to 3" in size, learn how Equilibar can provide lightning fast back pressure control through very wide flow rate ranges.
How Back Pressure Valves work
A back pressure valve is a control valve that is configured to control the pressure upstream. Back pressure control valves open to lower the upstream pressure and close to increase the upstream pressure. In recent years, the most common control method is the digital process controller with PID (proportional / integral / derivative) algorithm. A pressure transmitter upstream of the back pressure valve sends the process value to the controller, and the controller sends a variable output to the control valve so that the ultimate set point is achieved. The process controller can be tuned to react as fast as the valve actuator and fluid compressibility will allow. In large systems, however, there can be a lag in responsiveness of several seconds if the flow rate through the piping changes abruptly.
In former years, back pressure control valves were also pilot-actuated by pnuematic feedback loops.
Back Pressure Regulators
A back pressure regulator functions in a similar way, working to control its upstream pressure. It also opens to lower upstream pressure and closes to raise upstream pressure. All regulators also have a type of valve mechanism inside as well. However, the common use of the term "regulator" implies that the control is close-coupled through a direct or native feedback mechanism. Most spring type pressure regulators balance pressure on the wetted side of a diaphragm against an adjustable spring force on the other side of the diaphragm. The diaphragm is coupled directly to a type of control valve that responds to slight movements of the diaphragm. In the case of a back pressure regulator, the spring holds the control valve closed until the inlet pressure (exposed to the wetted side of the diaphragm) is able to raise the diaphragm and control valve stem up and establish flow. The system natively finds the proper position where the inlet pressure is held at the desired set-point. This simple mechanical feedback mechanism is extremely fast and reliable.
Choosing between Back Pressure Valves and Back Pressure Regulators
For larger pipe sizes, typically above 2", back pressure control valves are considered a more economical solution. This is probably due to the fact that it is expensive and awkward to expose a large wetted stream to the underside of a wetted diaphragm. By using a control valve configured for back pressure control, the size of the wetted valve is minimized, and the controller can command the valve by one of several means, such as a motorized actuator or pneumatic actuator.
For smaller piping, the relative cost of having the wetted diaphragm chamber is considered minor compared to the expense of installing, tuning, and maintaining an active PID control loop. These smaller systems benefit from the simplicity and fast responsiveness of the mechanical regulator, even if a process computer and pressure sensor is present in the system.
Equilibar Back Pressure Control
Equilibar precision back pressure regulators work in a different way from spring-type back pressure regulators. They use an air pressure on the top of the diaphragm instead of a spring, and also use direct diaphragm sealing instead of a traditional valve seat. However, their lightning fast response and zero hysteresis give them certain performance advantages over either the spring type back pressure regulator or the back pressure control valve.
Equilibar back pressure regulators are currently provided in sizes up to 3" pipe size. However, larger size regulators can be built upon request. Learn more about our unique back pressure regulator technology and our product details.
