Equilibar multi-orifice diaphragm valves are now being adapted to control flow rate in complex scenarios for applications that cannot be solved by traditional flow control methods. Some of the demanding applications may include:
- Flow coefficient (Cv) ranges wider than traditional valves (>100:1)
- Extremely low DP and extremely high DP
- Two-phase, phase-change and supercritical states
- Continuous flow chemistry
- Sanitary applications
How it Works in Flow Control
In a flow control configuration, the Equilibar back pressure regulator (BPR) uses a pilot pressure controller and a flow meter in a control loop. (See schematic at right). A proportional-integral-derivative (PID) controller monitors input from a flow transmitter (FT) and adjusts the pilot pressure to control flow. An electro-pneumatic transducer (E/P) translates the electronic signal from the PID into a pressure signal for the pilot controller. Flow is decreased by raising the pilot pressure and increased by lowering the pilot pressure.
Pressure and flow have an inverse relationship, so the control scheme will be set up differently for flow and pressure control. In flow-control operations, the PID loop must be used in direct mode instead of the more common inverse mode, because pressure must be increased in response to an increase in flow. See the graph to the right for a comparison of flow through a traditional globe control valve (blue) and a direct-sealing diaphragm valve (red) in response to actuation pressure.
This video demonstrates how it works
Reasons to Consider an Equilibar Back Pressure Regulator for Flow Control
Operates Across a Wide Range of Flow Coefficient (Cv)
One characteristic of traditional flow control valves is that of limited flow range (or the max/min ratio of effective Cv). Most control valves operating in research and process industries are limited to between a 10:1 and 15:1 ratio. An Equilibar back pressure regulator can easily operate in a Cv range greater than 100:1.
Read our article in Flow Control Magazine at the right which describes a specific customer application with the range of flow Cv from 1E-5 to 2E-2 and a turndown ratio of approximately 2500:1.
Learn more about Equilibar’s flow control valve with wide flow range.
Controls Multi-Phase Fluids
The unique design of the Equilibar® back pressure regulator enables it to handle two-phase or mixed-phase flow streams while maintaining high precision. This can include gas/liquid processes, water/oil flow streams, or supercritical fluids.
Traditional back pressure regulators use a single annular valve seat, often very small, so that when slugs of liquid flood the valve throat, volumetric flow rate drops suddenly as the denser fluid is accelerated through orifice. This momentary reduction in volumetric flow disrupts the stability of the upstream process pressure.
The unique Equilibar technology uses a direct sealing diaphragm over multiple orifices to control the pressure drop. The supple diaphragm can vary its proximity to the orifices nearly instantaneously to adjust to the varying valve coefficient (Cv) requirements of the various phases.
Read our article in Flow Control Magazine at right which describes a specific customer using an Equilibar BPR for flow control of multi phase fluid.
Isolates from Downstream Pressure Changes
An Equilibar BPR provides a buffer against changes in downstream pressure. A back pressure regulator will automatically adjust to keep its inlet pressure at setpoint regardless of changes at the outlet port. When using a traditional flow control valve (FCV), any change in downstream pressure will require a PID control adjustment to remain stable.
Equilibar dome-loaded BPRs have ultra high resolution, zero hysteresis and zero dead-band. This can be useful where traditional control valve deadband (or “stiction”) do not have adequate precision. Small adjustments may be made to the differential pressure resulting in high resolution pressure control. See details for high resolution flow control application in temperature control.
Demanding Service Conditions
Equilibar BPRs have only one moving part and are therefore easily configurable for the following severe and demanding service conditions:
Continuous Flow Reactions
Controlling pressure in continuous flow chemistry is important for phase control, residence time, reaction speed and equilibrium management. For instance, reaction temperature is a key component in reaction efficiency but at high enough temperatures, a reagent can reach boiling point which negatively impacts the reaction. Controlling reaction pressure by adding a back pressure regulator to the outlet of the reactor can prevent reagent boiling.