Optimising pharma-grade water flow measurement

Damien Moran, Field Segment Manager, Hygienic-Pharmaceutical at Bürkert, discusses surface acoustic wave (SAW) technology and its comparison to traditional measurement sensors for purified water and clean utilities

For any purified water metering device in the pharmaceutical sector, hygiene is fundamental. Measurement of water for clean utilities applications, from OEMs developing skids through to end users requiring process flush cycles, demands a hygienic flow meter. This means a sensor that’s free of mechanical obstructions where bacteria can accumulate, and with a free flow that enables complete flushing and prevents collection of water residue. For processes that involve purified water (PW), deionised water (DI) and water for injection (WFI), the sensor also has to be able to accurately measure fluids with low conductivity.

Volumetric or mass flow measurement?

Combined with the essential hygienic design and low conductivity measurement capability, the flow meter requires the necessary accuracy to achieve product quality and to help maintain process cost efficiency. For these reasons, mass flow meters (MFM), such as those featuring Coriolis sensors, are often specified.

However, for purified water hygienic pharmaceutical applications, measurement of volumetric flow, rather than mass-flow, is most commonly the only requirement. Providing the flow meter can accurately measure real time flow rate, total flow and flow velocity, the additional technology of an MFM to measure grams and kilograms is redundant and an unnecessary extra cost. What’s more, an MFM is also bettered in hygienic terms.

Surface acoustic wave technology

Measurement using surface acoustic waves (SAW), which occur naturally such as in seismic activity, is tried and tested technology dating back to 1885. Used for the in-line flow measurement of fluids, the technology provides highly accurate volumetric measurement.

Bürkert’s FLOWave flow meter generates surface acoustic waves that travel from the tube’s surface, through the process fluid at a controlled angle in both directions. Calculating time differences of the waves proportional to the flow, FLOWave determines real time flow rate, total flow and flow velocity in m3/hr or l/min, measuring irrespective of water conductivity.

Hygienic design

Based on a completely obstruction-free tube, the key advantage of SAW technology is its hygienic performance, making FLOWave the most hygienic design of flow meter for purified water applications. The straight-through measuring tube means there are no protruding components to come into contact with the purified water, removing the potential threat of contamination through accumulated bacteria. Some MFMs incorporate a u-bend, preventing water from fully draining away with the potential for bacterial growth. Instead, FLOWave enables free-draining flush for a hygienic clean in place (CIP) process.

Constructed from 316L stainless steel, this prevents corrosion of the flow meter and the bacteria that can develop within it. The smooth, polished design also conforms with the highest grades of pharmaceutical standards.

Measurement performance

As a result of the precision of the surface acoustic wave technology, FLOWave flow meters achieve an accuracy of 0.4% of the measured value, repeatable to just 0.2%. These margins are capable of providing the required performance for any purified water pharmaceutical application including batching, and as there are no moving parts to wear, this level of accuracy endures over time. For the same reason, FLOWave is also maintenance-free, saving time and cost.

FLOWave can also simultaneously measure real time flow rate, total flow and velocity. Measurement of flow velocity in a clean utility application is useful to ensure that a minimum flow rate within the loop, for example 0.9 – 1.5 m/s turbulent flow, is maintained at all times. This prevents build-up of biofilms and helps maintain total hygiene, and it can also be used to confirm water availability at points of use (POU) across the facility. Flow rate and velocity can be combined to measure usage at certain points in the system, with flow meters on both the supply and the return, to optimise water use and increase process efficiency.

For improved operational use, FLOWave also maintains water pressure throughout the tube, meaning that it doesn’t create a pressure drop at the outflow that would otherwise require a higher pressure at source. Unlike a meter with obstructions within the flow, FLOWave’s straight-through tube is free of pressure-reducing restrictions. The advantages of a zero pressure drop flow meter also accumulate with a greater number of flow meters incorporated into a system, for example if multiple POUs are monitored.

Easy, compliant integration

Compared to other flow meters typically used for purified water pharmaceutical applications, FLOWave is extremely lightweight and compact. As a result, it can be easily integrated into an existing process and takes up less factory footprint for newly designed systems and skids. As FLOWave can be held in one hand, it’s also fast and simple to install by a single technician and doesn’t require lifting apparatus. The flow meter is also configured for all modern digital communication protocols.

Crucially, FLOWave also meets the essential pharmaceutical industry compliance, including an FDA certificate of conformity and certification of compliance ASME BPE, meaning that it’s approved to the most robust regulations.

The tried and tested SAW technology not only makes FLOWave an accurate and effective flowmeter for purified water pharmaceutical applications, but also means that it is extremely cost-effective. If volumetric flow measurement for low conductivity hygienic applications is required, SAW technology flow meters should be considered.

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