Globe valves carrying out control
May 2016
Valves, Actuators & Pump Control
Quite often, a simple On/Off function is not sufficient to exert flexible influence on the volumetric flow in a pipe. In order to do so the valve must precisely adjust to the range adapted to the regulating task. Therefore, regulating globe valves are equipped with specially designed cones instead of the conventional open/closed valve plugs. No matter whether in the chemical industry, power stations, food processing or in any other application of the process industry, regulation of fluids covers a wide area. In order to achieve the desired control the characteristics of different types of regulating cones are chosen to suit the application.
GEMÜ globe valves can be equipped with different types of regulating cones, providing precise opening within a defined regulation curve. With increasing opening of the valve, the regulating cone changes the annular gap at the valve seat providing the requested control characteristics. A suitable valve equipped with the right type of regulating cone and a suitable actuator is necessary for optimum functionality. The most frequently used control characteristics are linear and equal-percentage 1:25 and 1:50. Linear means that the flow increases linearly with the opening stroke of the valve. The flow is 50% at the 50% open valve position. This provides perfect valve control, over the whole stroke range.
Depending on the type of globe valve and the nominal size, control valve bodies may have widely different geometries. In the case of small nominal sizes and high pressures, regulating ‘needles’ are used for their high precision control function. For larger valve sizes, modified regulating ‘cones’ or ‘cages’ are preferred.
The GEMÜ 536 is a pneumatically operated 2/2-way valve having a low maintenance membrane actuator. It is constructed to cover all universal operations over a long life cycle with low maintenance requirements. The valve plug is fixed to the spindle in such a way as to allow flexing during closure, in order to ensure tight shut-off. The valve spindle is sealed by a self-adjusting gland, which provides reliable sealing over a long service life. A wiper ring fitted in front of the gland packing protects it against contamination and damage. These features result in advantages such as robust design, adapted flow capabilities, exact controllability and usability in a broad range of operating pressures and temperatures. The valve can be equipped with a series of accessories, for instance stroke limiter, optical and electrical position indicator, manual override and electro-pneumatic positioner.
Depending on the application details and operating conditions, GEMÜ´s team of specialists will assist to find the best solution. This ensures benefits like safety for operators and the environment at the best cost-performance ratio.
For more information contact Claudio Darpin, GEMÜ Valves Africa, +27 (0)11 462 7795, [email protected], www.gemue.co.za
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