Flow Control | Equilibar Back Pressure Valves in Complex Applications

Flow Control Using Equilibar Back Pressure Regulators

How Equilibar BPRs offer advantages for complex applications

  • schematic of how equilibar back pressure regulator works in flow control
Some complex manufacturing processes require process control solutions that can perform in demanding applications. Equilibar® direct-sealing diaphragm valves with dome-loaded actuation have been used for over 10 years to control back pressure. They are especially well-suited for processes where high turn down ratio, high precision and two-phase flow are required. Equilibar multi-orifice diaphragm valves are now being adapted to control flow rate in complex scenarios and offering advantages for applications that cannot be solved by traditional 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

How it Works

For this application, the Equilibar back pressure regulator (BPR) operates using 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 up to the media supply pressure. It is increased by lowering the pilot pressure below the media supply pressure.

Pressure and flow have an inverse relationship, so the control scheme will be set up differently for each one. 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.

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Reasons to Consider an Equilibar Back Pressure Regulator

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.

Isolation from Downstream Pressure Changes

By using an Equilibar BPR, your system is automatically buffered 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 FCVs, any change in downstream pressure will require a PID control adjustment that may be disruptive to your process.

High Resolution

Equilibar dome-loaded BPRs have ultra high resolution and 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.

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.

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GS4 Back Pressure Regulator with QPV pilot

Equilibar® direct-sealing diaphragm valve with dome-loaded actuation

schematic of how equilibar back pressure regulator works to control flow

How the Direct-Sealing Diaphragm Valve works in Flow Control Operation

Graph of flow versus actuation for globe valve and Equilibar valve

 

March 2019 Flow Control Magazine

Equilibar is featured in the March 2019 issue of Flow Control. Read the full article here.

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