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This feature’s valve is a snazzy Type 8560 butterfly valve toting a shiny new 1061 piston actuator topped off with a 3610 positioner. The valve exhibited a very sluggish response as it tried to exit its seat. A complete physical (Dynamic Scan Test) was performed on the valve.
The Positioner signature verified the valve’s complaint of sluggish performance as it left the seat. Here we see a very excessive Dynamic Error Band (D.E.B.) value of over 18% as the valve was initially demanded to move. A D.E.B. of less then 4% would be expected from this valve construction. The D.E.B. value is an excellent indicator as to the response of a valve assembly when the test is run per FlowScanner guidelines. The higher the D.E.B., the less responsive the valve assembly. We now realize that the valve is not responding as it should.
The tests showed that the valve’s body was in very good physical condition. There was no excessive friction during the exiting of the seat, nor through the remainder of the valve stroke as seen here in the Valve signature. The travel was within acceptable limits. The overall appearance was just what one would expect from a valve of this type. Being reasonably assured that the valve, actuator, and positioner were mechanically sound, we could now concentrate our efforts on calibration issues. In viewing the Actuator Stroke, Actuator Return, and Supply pressures against time, we realized that the Positioner’s relay crossover adjustment was much too high.
The crossover should be adjusted to approximately 75% of supply pressure to provide for adequate air spring stiffness plus allow for responsiveness of the valve. As you can see here, the crossover is bumping 100%. We were able to adjust the relay crossover to what you see below by performing a calibration procedure.
Adjusting the relay crossover to the correct pressure value resulted in the excellent (responsive) valve performance shown below. |
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