Traditional back pressure valve (BPV) designs use a rising stem globe type valve to modulate the flow of the process fluid. The back pressure control valve can really only influence the flow and cannot control the pressure directly. To control the pressure an external control loop is required. These control loops can be a complicated mechanical feedback regulator but are more often an electronic PID loop using a pressure transmitter as feedback.
Equilibar Valves are Simpler and More Accurate
Equilibar back pressure valves work in a completely different way than traditional back pressure control valves. Equilibar back pressure valves control pressure in a precise one-to-one ratio to a pilot signal that is applied to the top of a diaphragm. The other side of the diaphragm is exposed to the process media pressure that is being controlled. The diaphragm moves in response to a sensitive and precise 1:1 force balance between the media pressure and the pilot pressure. The pilot pressure is provided by a simple mechanical regulator or with a remotely controlled electronic pressure regulator. The internal operation of the Equilibar valve can be seen in the cross section diagram. The diaphragm is the only moving part and acts as the valve member by directly sealing against the internal orifices.
Advantages of Equilibar Over Back Pressure Control Valves
Easiest Control Loop
The diaphragm inside the Equilibar back pressure valve is its own closed loop system. The precise 1:1 pressure balance maintained by the diaphragm means that the Equilibar valve will automatically modulate the flow rate to keep the upstream pressure matched to the pressure setpoint. A complicated feedback regulator or hard to tune PID loop is not required
Accurate and Stable Back Pressure Control
The diaphragm inside the Equilibar is frictionless and sensitive to very small changes in the upstream pressure. This diaphragm compensates for system changes automatically and immediately to keep the pressure matched to the pilot pressure.
High Speed Response
The diaphragm is loaded with a compressed gas pilot signal. This allows the diaphragm to respond to changes in the upstream pressure or flow rate within 10mS. The compressed gas on the pilot does not inhibit or dampen the diaphragm’s ability to respond quickly.
High Flow Rate Turn Down Ratio
The Equilibar back pressure valve controls pressure using a multiple orifice design. As the flow rate increases or decreases more or fewer orifices will be brought in to play by the action of the diaphragm. Only one orifice might be required to modulate for very low flow rates while multiple orifices will be used when higher flow rates or surges in the flow occur. Flow rate turn down ratios of over 100,000:1 are achievable.
High Pressure Turn Down Ratio
The diaphragm inside the Equilibar regulator is flexible and strong as it is manufactured from modern polymers. This diaphragm allows the valve to control back pressure over a very wide range. In example, a 1000psi control valve could be expected to control pressures as low as 25psi while maintaining accuracy.
A Note About Back Pressure Valve Terminology
The term back pressure valve and back pressure regulator are often used interchangeably. The Equilibar valves shown on this page are more accurately called back pressure regulators. However, Equilibar uses the term back pressure valve to describe regulators which are 1.5 inch size or larger while reserving the term back pressure regulator to describe products that are smaller than 1.5 inches. For a full discussion on this topic see the page BPV versus BPV.
Typical control valve using PID feedback control to accomplish back pressure control. This approach can be complex, sluggish, and has limited flow range
An electronic pressure regulator can directly command the pilot of the Equilibar back pressure valve, with no PID, tuning, or sluggish performance. The Equilibar is capable of handling flow rate variations up to 1000:1, compared to 15:1 for most traditional control valves.