Chemical Technology August 2016

FOCUS ON PUMPS AND VALVES

Valves, the actuators that move them, and the electronic circuits that control them, are all subject to the effects of aging soon after they are in- stalled. The valve seat wears not only from the repeated seating of the valve, but from the liquid or gas that passes through it. Depending on the application, a valve can be stroked fromhundreds to tens of thousands of times over a one-year period. This amount of mechani- cal motion inevitably causes screws to reposition, springs to weaken and mechanical linkage to loosen. In addi- tion, electronic components change value over time. The results are valves that don’t fully open or close, close prematurely, or operate er- ratically and cause improper regulation of the gas or liquid under its control. This is more commonly referred to as “cali- bration drift.” To keep a systemoperating properly, a good preventative maintenance program that mandates periodic checks of valve positoners is required. These checks need to be conducted quickly to mini- mise down time. When these checks reveal calibration drift, recalibration of the elec- tronic valve positioner must be performed quickly. With the varied locations in which a valve can be installed and the difficulty in removing it, the equipment used to perform the checks must be brought to the valve positioner itself. Therefore, this “in-field” tester must be portable, easy to use and rugged. In-field valve positioner checks using a handheld ProcessMeter

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The tester, with signal sourc- ing, must simulate a controller connected to a valve position- er’s input. Through the controls on the ProcessMeter, the op- erator can set the positioner’s input current to a specified level and visually inspect the reaction of the valve’s position using the mechanical posi- tion indicator, the valve stem position or flow indicators. In addition, the process meter must continuously adjust the source current in a ramping or stepping fashion, allowing the user to check the valve’s linear- ity and response time. Always ensure that the per- sonnel responsible for the process you are working on are informed of your intentions prior to making any checks of valve operation. Be alert when touching any moving machinery. For more information contact: 010 595 1821 or email sales@comtest.co.za

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Features of GEMÜ Hygienic Valves: • FDA, USP, EHEDG approved • Safe sealing system • Optimal draining • Customized solutions • Manual, pneumatic or motorized actuation

GEMÜ VALVES AFRICA (PTY) LTD Stand 379, Northlands Business Park Hoogland Ext. 45

Northriding, Randburg Phone: (0)11 462 77 95 info@gemue.co.za www. gemu-group .com