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VEGA Americas: replacing displacers with guided wave radar saves money and increases efficiency

Published by , Editorial Assistant
Hydrocarbon Engineering,

Displacer measurement technology has been around for decades, so it comes as no surprise these mechanical sensors are a popular liquid level and interface measurement technology for refineries everywhere. Technology, however, is always changing, and electronic guided wave radar sensors offer refineries significant improvements in measurement accuracy and reliability with little to no effort to upgrade.

Displacer technology’s method of operation has remained mostly unchanged since its inception. A torque tube or spring-loaded float uses a liquid’s buoyancy to output a level or interface measurement. Because of this, fluctuating temperatures, build-up, and changing specific gravity can affect measurement accuracy. Additionally, vibrations, turbulence, corrosion can lead to mechanical failures.

Guided wave radar uses a probe to ‘guide’ microwave pulses to a product surface, which reflects some of the energy back to the sensor, and time-of-flight is used to calculate level and interface. These measurements are unaffected by changing pressure, temperature, or a product’s specific gravity. And with no moving parts, guided wave radar sensors can operate maintenance-free for years.

Displacers used in refineries are prone to constant maintenance, routine cleanings, frequent recalibrations, and regular replacements. The cost of ownership adds up quickly, especially when considering the number of measurements at a single refinery. Switching to guided wave radar is both easy and cost-effective.

Retrofitting new technology is a simple swap

Replacing displacer technology with an electronic sensor alternative is the ideal solution to stopping the merry go round of maintenance and cleaning. Guided wave radar sensors are commonly installed in bridles, bypass chambers, and pipes, all of which closely resemble a displacer cage. Retrofitting a guided wave radar into one of these displacer cages is a simple swap. It’s just a matter of identifying the type of displacer cage and configuring the guided wave radar to fit.

Displacer cages come in four different configurations: side to side, side to bottom, top to bottom, and top to side. Configurations without a pipe coming from the top – side to side and side to bottom – can easily be retrofitted. It’s simply a matter of removing the displacer electronics and float and installing a new, more reliable guided wave radar and a necessary flange. The other two configurations containing a vent pipe at the top require a little more creativity and finesse.

Different displacer configurations.

Traditionally, a guided wave radar requires a process connection at the top of the bridle or bypass chamber. Normally, this would prohibit using guided wave radar sensors in displacer cages with top to bottom and top to side configurations without costly pipe rerouting. Fortunately, level measurement instrumentation manufacturers such as VEGA have developed a more economical solution that provides reliable results.

Decreasing costs and reducing maintenance with creative solutions

A large refinery in the US had a failing displacer with a top to bottom configuration on their naphtha reboiler. Constant maintenance and repairs related to this displacer kept adding up, chipping away at the productivity and efficiency of the facility. It was time for a permanent fix.

The VEGAFLEX 81 is a guided wave radar, and users can order this sensor with a 90° bent rod segment. This way, the piping above and below remains intact, and maintenance crews only need to install the new guided wave radar where the displacer once was. The VEGAFLEX 81 can be customised and configured to fit any application. In addition to the 90° bent rod segment option, multiple flange possibilities can fit any process connection, a secure Bluetooth connection makes set-up and adjustment simple, and multiple communication outputs, including Modbus, HART, or Dual 4-20 mA, ensure this sensor can fit with any control system.

Refinery maintenance crews installed and calibrated the new guided wave radar in a single maintenance shift during a planned shutdown. Since then, the VEGAFLEX 81 has been working reliably and maintenance-free. This has not only saved the refinery time and money, but is it now getting a more reliable measurement on its naphtha reboiler.


Refineries have been using displacers for level and interface measurements for decades. These mechanical measurements take a lot of labour and time to keep them reliable and functional, and unfortunately, many refineries have grown accustomed to the extra costs. The single displacer at the West Coast refinery mentioned above needed maintenance every six to eight weeks, and it had become routine.

Breaking these costly habits and retrofitting displacer technology with guided wave radar sensors requires a fraction of the time and cost of maintaining old displacers. When refineries are willing to pause for a moment to take the long view, they may just find they can get a big return on investing in upgrades today. Newer level measurement technology will allow them to operate more productively, efficiently, and competitively for years to come.

Author: Tai Piazza, Industry Manager – Refining, VEGA Americas.

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