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DP Seals enjoys more sub-sea success with NOC

14 January 2015

DP Seals has delivered its first batch of critical components for the latest sensors designed at the National Oceanography Centre (NOC) in Southampton.

Photos: Kevin Saw, NOC and David Owsianka, NOC

The innovative, microfluidic sensors are among the smallest in situ oceanographic chemical sensors ever made and are to be deployed on a range of oceanographic platforms capable of operating at depths of several thousand metres.

For DP Seals, that meant designing a seal for the sensor’s seawater sampling system that would meet the most stringent standards of performance and reliability in an environment where high pressures, fluctuating chemical properties and very low temperatures would be an everyday reality.

The solution was a bonded rubber seal made from FFKM perfluoroelastomer – a material in which the company has unrivalled expertise – and with the initial order successfully fulfilled, DP Seals is now developing similar components for other applications.

“It’s the first time we’ve worked with DP Seals,” said NOC’s Kevin Saw, “and we were hugely impressed by their complete understanding of our requirements and their ability to meet our brief so effectively.

Bonded seals for miniature sensors
NOC is one of the foremost institutions of its kind in the world, and among its on-going projects in recent years has been the development of miniaturised sensors to directly measure changing nitrate levels in rivers and oceans, and variations in ocean acidity caused by increases in atmospheric CO2.

To achieve this with the accuracy and resilience required, their latest microfluidic designs needed the 3.3mm diameter pump cylinders and pistons to be sealed to an exceptionally stringent standard – something which conventional o-rings and quad rings proved incapable of achieving.

With an endurance target of 100,000 cycles, a bonded sealing element was proposed, and in October 2012, DP Seals were briefed on this vital component.

FFKM the first choice
Considering the environment in which the sensors might operate – where high pressures, fluctuating chemical properties and very low temperatures could all be critical factors – it soon became clear that only a seal made from FFKM perfluoroelastomer would meet NOC’s requirements.

While many companies believe FFKM is difficult to mould and unjustifiably expensive to produce, we knew from our previous work with the material that it not only had the outstanding characteristics essential for predictable performance and total reliability, but could also be successfully produced to a realistic budget and within a sensible time scale.

An 18-month development programme ensued and initial samples were produced, but tests showed that fluid leaked past the seal after less than 2,000 cycles – so further samples with improved surface quality and less mould artefacts were made and bench-tested in NOC’s labs.  This time there was no leakage at all until 75,000 cycles and only a slight loss of performance at the 100,000 target.

Increasing the seal diameter to eliminate the leak entirely proved to be a red herring, and after some issues with stray bonding agent were successfully resolved, the first production batch of seals was delivered and fitted. On-going bench testing at NOC has recently achieved 178,000 trouble-free cycles, far in excess of the 100,000 cycle target. “This is a fantastic result and marks a step-change in reliability for our sensors” remarked NOC’s Kevin Saw.

Eyes on the prize
In early 2014, the new oceanic sensors – complete with seals – took part in the prestigious Wendy Schmidt Ocean Health XPrize, in which 23 organisations from around the world are competing for a $2 million prize, and having successfully passed Phase 1 of the competition, the NOC team moved into Phase 2 in September.

In addition, a nitrate sensor deployed in the Hampshire Avon has completed 25,000 cycles over a ten week period without any problems – and gathered very good data in the process.

Kevin Saw was quick to credit the role we played in the project. “It’s the first time we’ve worked with DP Seals,” he said, “and we were hugely impressed by their understanding of our requirements, their insights into materials selection and their ability to meet our brief so effectively.”

As a result of this collaboration, we are now working on tooling for a similar seal for larger 9.8mm pistons and this offers NOC real potential to finally achieve its 100,000 cycle endurance target across their full range and further enhance their reputation for producing exceptionally reliable, world-leading sensors.

Key to illustration
The 3.3mm diameter piston operates in a boroslilicate glass cylinder, obtaining sample fluids and processing them in the miniaturised sensor located in the cylindrical base of the unit shown above. The unit can be used in any of the NOC's impressive fleet of Gliders and mini-subs shown here.


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