18 July 2019
In this blog, I would like to explain to you how our back pressure regulators can be applied to not only control pressure, but also to control flow. Even in situations with many unknowns! This blog was also published as a Linkedin article – please share!
Unknown parameters in your process
Before you, as an engineer, build an experiment set-up, the conditions under which your process will operate need to be defined. The optimal process conditions often either are the parameters that need to be investigated or are not yet determined. Therefore the process conditions often are only defined very broadly or unknown, leaving you with a difficult task: You don’t want to limit your operating conditions to boundaries upfront, as you don’t know your required values yet. You will thus often end up with a large variation in design specifications. In many cases, commercially available instrumentation will not adequately meet these requirements.
Flow rates with 1:50 turndown ratio combined with a pressure range with a 1:50 turndown ratio and media with a large variation in density and viscosity are no exception. Wouldn’t it be great to have a valve that doesn’t limit the operating conditions before you start your experiments? Would you prefer a valve that allows you to try out all possible variations in flow rate, pressure range, and media density and viscosity?
How Equilibar ® technology can help
Equilibar dome-loaded back pressure regulators are uniquely designed to hold pressure over an extremely wide flow and pressure range. This is achieved by balancing three-way-pressure around a diaphragm in the regulator
that seals the multiple inlet- and outlet orifices. When the diaphragm sealing the orifices is pushed onto the body, the flow is blocked. By modulating the pressure against the diaphragm, the flow changes. This way, the characteristic working principle of the Equilibar Back Pressure Regulator can also benefit level or flow control applications.
Imagine a standard lab scale flow sensor with onboard PID controller being connected to a direct operated proportional valve, in turn being integrated into the cap of a dome-loaded Equilibar regulator. The upstream pressure from a gas or liquid supply is set at the inlet of the Coriolis sensor; a gas bottle with N2 or air is used to set the reference pressure.
On the right you see a schematic drawing of such a set-up – a larger version of this image is at the top of this article – and an example with the Bronkhorst Cori-Flow below.
How does it work?
When the setpoint to the mass flow controller is set to zero, the integrated proportional valve needs to be fully open. This can be achieved by inverting the control signal in the PID controller. With the proportional valve fully opened, the diaphragm is pushed onto the orifices of the dome-loaded valve resulting in zero flow. When a setpoint > 0 is applied, the integrated proportional valve will close. A small bleed through a – specifically for this purpose designed- flow restrictor, allows a bit of reference gas to escape from the dome of the Equilibar regulator, causing a decrease of the reference pressure. Once the pressure on top of the diaphragm matches the upstream pressure in the Coriolis sensor, the diaphragm will lift, allowing an increase of the flow through the sensor. The PID controller will now find the right position for the proportional valve to balance the flow into the dome and the bleed allowing the diaphragm to find the exactly right position to keep the flow constant, at the requested flow rate.
Do you think this sounds complicated? The Equilibar® Back Pressure Regulator with its unique features is capable of finding this pressure balance without friction and at high precision.
Benefits of two-stage-control-loop
If you can control the required flow with a direct valve, it may be advisable to do so. However, more and more applications have an increasing demand for a larger turndown ratio than traditional valves can offer. This demand is caused by a combination of flow turndown ratio, a large variation of inlet and/or outlet pressure, and changing properties of the controlled media affecting the flow-coefficient of the valve.
The accuracy and broad control rangeability of the Equilibar ® Back Pressure Regulators are primary reasons for choosing this product combination and satisfy this demand. Another great benefit of this combination is the possibility to control pressure independently of the delta-P over the valve. Most direct control valves are only capable of working with a fixedpressure drop.
When you choose this combination with an Equilibar Back Pressure Regulator, you can handle variable pressure drops in your process from 2 up to 200 bar, because the pressure drop is overcome in the outlet orifices of the valve.
Another unique feature is the huge rangeability: One valve can handle a flow coefficient turndown ratio of 1:100.000, allowing it to operate with both liquid and gas. The Cv range of the combination shown below goes all the way from 10E-8 up to 0,05.
Furthermore, Equilibar back pressure regulators can handle supercritical media as well. This means we can build compact mass flow controllers for applications with supercritical CO2, propylene, ethelene, etc. that can both measure and control flow with unsurpassed accuracy and stability without blocking or clogging the valve due to freezing effects.
Last but not least, Equilibar valves are famous for it easy maintenance. Each valve contains only 5 parts, held together with 6 or 8 bolts. Disassembling and cleaning is very easy. After assembling the valve it is ready to operate. No special adjustments are required. This blog and video show you just how easy rebuilding really is.
Want to know more?
Since no process is the same and you know your application better than anyone, we encourage you to share your flow control challenge with us. We will be glad to help you configure your set-up in such a way that you can get the most out of your application and process. Based on our experience with previous buyers and users of the patented and innovative Equilibar ® Back Pressure Regulators, we can promise that its unique capabilities and performance will not disappoint you!