Taking the weight out of pressure regulation
31 May 2016
Suzanne Gill reports on the development of an innovative design for pressure regulation devices which results in a longer life, lightweight solution with a small footprint.
The knowledge gained in the research and development of turbines, jet engines and scramjets has been harnessed to create an innovative pressure regulation/pressure reducing valve (PRV) technology by Oxford Flow, a technology business originating from Oxford University.
Professor Tom Povey was behind the development, which aimed to create a regulator solution capable of handling the very high pressure and flows typically found when conducting research and development into applications for gas turbines, jet engines and scramjets.
The majority of traditional pressure regulation and control products on the market today utilise a diaphragm as the measuring element. This modulates with the changing pressure and so needs to remain flexible to provide accurate control. Loss of flexibility of the diaphragm is one common route cause of pressure regulator failure through fatigue, erosion or embrittlement, and so the devices require frequent inspection and regular replacement.
Prof Povey and his team have developed a compact, high precision regulator with only one moving part which eliminates the need for the more complex and failure prone diaphragm arrangements found in most regulator designs.
Prof Povey explained: “Our design is not based on any current regulator design. We went back to the drawing board to look at new design concepts having identified the minimum requirements for a device and went on to create something from first principles which would offer a devices able to provide advanced and accurate pressure control.” The design features just one moving part and has only one deformable part – a seal – so the wear life is anticipated to be very long, making it suitable for use in applications where the cost of failure is greatest – for example in subsea oil and gas applications.
The resulting PRV is based around a direct sensing piston regulator which has simplified pressure regulator design and removed the need for a diaphragm. The design of the Oxford Flow PRVs enables them to be manufactured from a variety of different materials to suit a wide range of applications including corrosive atmospheres and extremes of temperature.
Being designed to fit between standard flanges in a pipeline the original IHF series Oxford regulator is a very compact device. One side of the piston is exposed to downstream pipeline pressure; the other is balanced against a pressure cavity controlled by a pilot regulator. The sleeved piston actuator operates over an optimised feed hole configuration to provide precise, stable control across the entire operating range.
During operation, the piston moves inward, reducing the size of the cavity when the downstream pipeline pressure exceeds that within the pressure cavity set by the pilot regulator. The movement of the piston actuator progressively covers the feed holes, reducing the flow rate to maintain a stable downstream pressure.
When demand increases the downstream pressure falls below that set by the pilot and the reverse operation occurs. The cavity expands, as the pilot feeds it, uncovering the feed holes, which increases flow and maintains a stable downstream pressure.
Extensive testing of the IHF PRV against market-leading pressure regulators was conducted in a dedicated test facility. The comparisons across all performance parameters demonstrate its benefits, including:
• Maximum flow rates up.
• Increased accuracy – response times down.
• Minimum pressure drops reduced.
• Lower noise emissions.
The tests also demonstrated that the Oxford Flow device provides new levels of outlet pressure control accuracy across varying inlet pressures and flow rate demands.
“The product range continues to evolve,” said Prof Povey. “Fundamental design principles remain the same but we are developing the technology to suit the needs of other industry sectors by offering it in different configurations.” The Oxford Flow design, for example, can result in a pressure regulator that are less than 10% of the weight of a typical pressure regulator in high pressure applications.
With its combination of compact size along with reliable precision pressure control for all gases, including natural gas and other fuel gasses such as LPG, the IM PRV, for example, is well suited to use in natural gas pipelines because it is a compact device and is completely non-venting. It could also be utilised in high-specification clean application high-pressure fluid lines – such as nuclear reactors and high pressure water and steam systems.
The IM offers ultra-high flow capacity and accuracy for gas and fluid applications. It is suited to use a monitor regulator with active IM or an IHF series regulator. The optimised flow path has minimal restrictions reducing turbulence, noise and minimum pressure differentials. This also makes the design suitable for handling liquids and dirty fluids such as crude oil or drilling fluids. Manufactured in 316 stainless steel and rated to 110 Bar, the IM regulator saves space and fits neatly between standard flanges in a wafer-type installation.
The IP is another variant of the original design, developed to offer a low-cost solution for the water industry. “The specification drivers in the water sector are installation cost and ongoing maintenance costs and size,” said Prof Povey. The Oxford Flow IP PRV is designed to control regional pipes of around 4-6in in diameter. The regulators weigh around 2kg, compared to a more traditional regulator designed to do the same job at between 50kg and 70kg. This size and weight reduction enables operators in the water sector to minimise trench access and with just one moving part, helps reduce the need for maintenance and replacement. Further, the device can be manufactured from polymers that are approved for potable water use.
The team at Oxford Flow are continuing to innovate, and are developing more product variants based around the same design concept. The products are manufactured in the UK.
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