This article describes how valve actuator instrument tubing can be subject to abuse and damage from vibration and environmental extremes, and shows how Fisher actuators solve these types of problems.
Valve actuator instrument tubing is often subject to abuse. It can be damaged by rough handling during shipping or transport. Workers tend to lean ladders against it, stand on it, pick up valves by grabbing onto the tubing, overtighten connections and hang onto it for support.
Mike Sommerlot, Product Marketing Manager for Fisher Sliding Stem Valves at Emerson Automation Solutions, describes how to solve these and other problems in his article, Eliminating Troublesome Tubing:
Excessive vibration can damage a control valve’s actuator tubing by causing fatigue damage at or near the nut/ferrule location, resulting in leakage. Leakage causes pressure to be lost, and without pressure in the tubing, the actuator cannot be controlled. Leakage also requires increased supply pressure, adding to operational costs.
Emerson conducted market research, including a customer analysis along with surveys to our sales offices and service sector, in order to identify what issues customers bring up most often with respect to spring and diaphragm actuation. Mike adds:
Along with these activities, we reviewed our Quality Assurance archive for a three-year period to understand the root-causes and frequency of actuation-related warranty claims. We determined that the two biggest problems for customers were tubing/fitting issues and actuators being assembled incorrectly, often directly related to tubing and fittings.
A solution to both of these issues was eliminating external tubing. Emerson created an internal air passage in the actuator yoke to eliminate external tubing, and cast an internal air passage into the yoke of a Model 667 size i pneumatic actuator. Mike explains how this solves problems:
This eliminates the need for external tubing from Emerson’s Fisher FIELDVUE digital positioner to the actuator diaphragm casing. This configuration eliminates potential leak paths that can develop at tubing and fitting connections, as well as reduces the possibility of damage to tubing through improper use.
The internal air passage also simplifies installation. The Model 667 size i allows the FIELDVUE positioner to mount using 50% fewer mounting parts, reducing installation time and expense. Also, there is no tubing to bend or cut, no ferrules or nuts to attach, and no chance of losing or mismatching those parts.
Mike summarizes the benefits:
Eliminating external tubing is a significant improvement in actuator technology. By eliminating tubing, valve actuators become more reliable, less prone to vibration problems, and immune to damage from misuse and inclement weather.