A new vision for valve maintenance
February 2008
Valves, Actuators & Pump Control
The new generation of valve sensor packages from Tyco are designed to capture and interpret the data that can be obtained from a valve when it opens and closes. The system is designed to reduce unnecessary downtime while still reliably warning plant operators in good time when intervention is needed.
Valve travel time typically might be a few hundred milliseconds for smaller valves or of the order of one or two seconds or minutes for large ones. Analysis of this travel time can yield useful information. A trend towards longer and longer time values for breakaway could indicate that something is sticking, for example, or that internal deposits are accumulating.
The AVID XR contains a Hall effect sensor which measures the exact valve position and gives precise position feedback. Pressure sensors measure the input and exhaust pressures, as well as the differential pressure between the opening and closing ports. The pressure measurement is important since it is a contributing factor to the overall travel time. The fully encapsulated electronics is equipped with serial communication via high speed fieldbus or the wireless Bluetooth protocol.
The hardware is supported by the XamineR software designed to calibrate, interrogate, and maintain the system. Raw sensor data can be displayed as in Figures 1 and 2, which are time plots of the valve's opening and closing. The red line is the position of the valve; the dark green is the air supply; the blue is the differential air pressure and the yellow is the exhaust. Inspection shows that these curves differ from valve to valve and vary with time and usage. Testing has revealed a number of different characteristics to look for in the curve shapes that indicate potential problems. To date Tyco engineers have logged about 40 specific signature errors that can be used to alert operators.
Figure 1
Figure 1 shows the opening signature of a typical, correctly functioning, quarter turn valve with single acting actuator. The actuator differential pressure (blue curve) rises sharply in the first 0,25 seconds, quickly attaining a 75% value and flattening off. The red curve represents the valve position. After breaking out of the seat, valve operation is smooth all the way to the open position. Figure 2 shows the curve of a closing valve. As soon as the actuator differential pressure drops the spring is decompressed and the valve starts to move smoothly into the closed position. Note that exhaust pressure peaks the moment the actuator is depressurised. Any deviation from the characteristic signature indicates a potential problem allowing timely intervention to prevent unnecessary downtime.
Figure 2
For more information contact Brian Allingham, Tyco Valves and Controls, +27 (0)11 454 4801, BAllingham@tyco-valves.com, www.tycovalves.com
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