PC-APR22-PG31.1_Layout 1 11/04/2022 16:09 Page 31


PUMPS, VALVES & ACTUATORS


demands system designers and operators give maximum attention to the mechanical elements required for optimum performance. One of those essential elements is the valve. Where the valve performs the role of a throttle device, weir type and straight-through diaphragm valves provide the most appropriate function. The diaphragm valve is an economic


ENCLOSED DIAPHRAGM DELIVERS BENEFITS T


KSB outlines some of the design benefits of its diaphragm valve range


he transfer of liquids in process operations is an everyday function in many sectors of industry, and therefore


recess on the cover flange of the valve body (Fig. 1). KSB says that its concept of the enclosed diaphragm delivers considerable advantages over other valve types. KSB’s diaphragm valve


solution for applications where the media being handled is corrosive or toxic, and where high levels of safety are paramount and normally satisfied by alloy metal valves which can be positioned close to pumps, bends, and in both horizontal and vertical pipelines. Furthermore, it has the advantage of eliminating the presence of a dead zone in the fluid chamber, preventing the accumulation of deposits. The general appeal of industrial diaphragm


valves is that none of the actuating elements in the valve bonnet come into contact with the media at any point in its passage through the valve. There can be no functional impairment or corrosion of the components. Valve operating reliability is, therefore, ensured at all times whether operation is intermittent or just once every few years. Common to virtually all makes of


diaphragm valves is the external body shape and internally the pre-drilled diaphragm, this being sandwiched between the bonnet and the valve body. However, there is an exception to this concept and it comes from KSB. Externally its weir type valves look just like all other diaphragm valves, but internally there is a difference: the diaphragm is wholly enclosed in the valve chamber within the


Sandwich design Diaphragm is fitted between bonnet and body in full force closure.


range encompasses the SISTO-KB straight- through valve and the SISTO 16/SISTO-20 weir type valves with enclosed diaphragm and spiral spring support (Fig. 2). Compliant with all relevant international standards, these valves are all available with a variety of linings, coatings and diaphragms and can be equipped with a range of actuators and accessories. “KSB’s unique sealing system consists of a


chambered diaphragm enclosed in the valve body backed up by a spiral spring support on the back of the diaphragm,” explained Marc Walker, UK Valves sales manager. “This


Fig.1: The diaphragm is wholly enclosed in the valve chamber within the recess on


the cover flange of the valve body


arrangement ensures that 100% of the diaphragm surface area is supported from the back at all times and prevents uneven pressure points when the valve is closed or in an intermediary position. On top of this the diaphragm pin is screwed into the compressor and is held through a balanced suspension while remaining manoeuvrable. This avoids specific point loading on the diaphragm during closure so that when pressure is increased the diaphragm cannot tear.” The perfect tightness and fixed position of


the diaphragm in its recess provides hermetic sealing to the atmosphere, thereby minimising the potential for media leakage and maximising the service life and the pressure limit of the diaphragm. The lining/coating technology used to


Fig. 2: The SISTO 16/SISTO-20 weir type valves with enclosed diaphragm and spiral spring support


Body-bonnet bolts go through the diaphragm. Risk of medium entering the bolted area unnoticed (thus, related risk of corrosion). No spiral support. Full pressure on the diaphragm (which can lead to deformation and faster rupture of the diaphragm).


KSB sealing system Diaphragm is chambered in the valve body with only partial force closure along the defined sealing area (instead of full force closure). Maximises the durability. Avoids material wear. Bolts are outside the diaphragm. In the case of leaks the latter become immediately noticeable.


Diaphragm is supported by spiral spring Pressure on the diaphragm is evenly absorbed by metal spring. Longer durability of the diaphragm due to reduced strain.


protect the valve body from abrasion and corrosion is another critical element in its appeal to a range industrial users. Ease of maintenance and replacement is a further advantage. Should it be necessary to replace the diaphragm this can be done without having to dismantle the valve body and without using specialist equipment or measuring tools. “KSB operates a vertically integrated


production and in-house manufacturing operation incorporating research and development resources,” continued Walker. “For example, use of FEM analysis in the development of diaphragms has allowed the company to speed up the introduction of new concepts, as well as contributing to reliability and performance”. KSB’s SISTO 16/SISTO-20 weir type diaphragm


valves and the swing check valve RSK/RSKS are available in the UK directly from its operating base in Loughborough.


KSB www.ksb.com


APRIL 2022 | PROCESS & CONTROL 31


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