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Re-engineering diaphragm valves

02 February 2018

The diaphragm valve provides an economical control solution for many process applications in a wide range of industries.

The ability to select valve seat and body materials to suit a range of fluids and pick from different control options has resulted in a very flexible product. Bürkert however has taken this a stage further in a project to re-engineer its diaphragm valves to continue to optimise performance while also improving longevity and operating efficiency.

The principal aims of the project were to increase Kv values, extend diaphragm lifetimes and improve the interface between the valve body and the diaphragm to make it easier to change the sealing materials. This would be achieved through improvements to the machining and polishing processes as well as changes to the geometry within the valve body.

Improving flow characteristics are best determined by the Kv value, which defines the flowrate through a fully open valve and is also the sizing factor used to calculate the pressure drop across the valve. As such, a higher value indicates less restricted flow and Bürkert aimed to improve the figures for the existing products by up to 40 percent. This in turn would reduce energy requirements and improve efficiency.

Improving geometry

One of the most significant changes came with the revised geometry of the forged valve bodies. Those with a nominal diameter between 8 and 50mm were re-engineered with four major alterations. The centre-line of the port connections was raised within the valve body; the bevel between the port connection and the diaphragm edge was optimised; the angle of the weir was increased, and a smoother weir edge radius was created.

These changes enabled faster flows through the valves which increased Kv values by up to 40 percent and ensured that all Bürkert’s valves in this range now exceed the industry average. This, in turn, will lead to reduced energy requirements for systems that integrate the new designs as well as improved diaphragm lifetimes.

Improving durability and versatility

The durability of the diaphragm is determined by its interaction with the valve body, the compressor and the actuator. Part of this project addressed the design of the compressor, which now has improved sealing properties as well as a bayonet coupling that is common to both elastomer and PTFE diaphragms.

This met the objective to increase the lifetime of the diaphragm and meet the additional challenge to improve the interchangeability of diaphragm materials, making it easy to change between PTFE and elastomer diaphragms. This improvement can also be implemented on valves that were manufactured prior to the introduction of the design changes in the valve bodies.

While advanced design technology has been used to create these developments, the projected improvements in performance have been confirmed through real-life test data. Processes involving steam, cold water and vacuum cycles have shown the life time of the EPDM diaphragm has been increased by a factor of 3 and to support this Bürkert diaphragm valves have successfully been tested under ASME BPE Appendix J exposure conditions (500 SIP/50 CIP exposure cycles).

The project has also made improvements to the finished surface of the forged valve body by removing the need for manual polishing and improving the electro-polishing process, with the surface roughness to less than 0.38 µm. In all, Bürkert’s development programme has made a valuable contribution to improving both the performance and the durability of its diaphragm valves.

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