View from the Other Side
Industrial users comment on their valve actuators
Earlier this year, CPLloyd Consulting performed a focused survey of industry end users in North America. The object was to gain a direct insight into their experiences and opinions on their electric valve actuators.
The facilities canvassed, included a major Canadian pipeline company, a large oil refining facility near San Francisco and a potable water treatment plant near Philadelphia, amongst other facilities. Collectively they operate several thousand valve actuators.
The actuators used are predominately the three phase electric type, although the refinery did have some pneumatic actuators on their modulating control valves.
The survey covered their opinions on the reliability, technical aspects and performance of the actuators. It also covered issues of training and support as well as additional features that could enhance the actuator performance.
Here are some of the edited highlights.
The overall opinion of the reliability of the actuators was very high. Little maintenance was required other than routine checks. In most cases these were the responsibility of the plant maintenance technicians, but in some instances the manufacturer’s support was required. All stressed that, when needed, they required almost instantly available telephone support and on-site support within 24 hours. The collective opinion of the support provided by their actuator manufacturers was quite positive.
Actuator failures were rare and usually the result of some external issue, such as vibration.
The biggest maintenance issue was the interface between the actuator and valve on threaded stem valves. The drive nut and stem require the most regular inspection and maintenance. This is because most stems are exposed to the elements and either the lubricating grease dissipates, or it collects dirt and grit that accelerates wear on the stem nut. At present there is no “smart” method of regularly measuring stem nut wear and occasionally the stem nut may fail. None of the companies interviewed regularly measure stem nut wear on their actuators. The current method of monitoring is a subjective visual check.
Advanced technology features
There were mixed views on the technology available in “smart” actuators. The pipeline companies were focused on reliability and although there was an appreciation of the capabilities of the smart features, they experienced difficulty in educating their technicians on interpreting the collectable data. This was also true of the refineries, but in one instance an individual took on the role of actuator specialist and regularly processed the data collected from the actuators.
Some technicians suggested that the information available to the end user could be displayed in a more user friendly and intuitive format. There seems to be an overload of information available from modern actuators. If this could be processed into information that requires no manufacturer-specific knowledge and was easily understandable by maintenance technicians, then it would be more helpful.
The refineries liked the digital bus communications facilities available with smart actuators, not only for control and indication, but also for diagnostic information. Often, a plant may have sophisticated asset management data collection and calibration capability, but not have the available expertise to utilize it.
The water treatment plant however, was disinterested in the additional data from the actuators. They had their own maintenance programs which did not need additional alerts or historical data from the actuators. This data was considered an unnecessary complication.
Commonly occurring problems
Sizing - When tendering equipment for a plant, a supplier of a motor operated valves (MOV) will have to bid competitively. The actuator has to be sized so that it is big enough to operate the valve, but no so big that it is uncompetitive. Most users in our survey, at one point, had been the victim of under-sizing by a supplier. This results in a failure of the MOV to operate after the effects of plant ageing have occurred. Ideally, correct sizing and the use of adequate factors of safety by the specifying engineers, contractors and suppliers should obviate this problem, but the issue still continues.
Most of those interviewed mentioned the difficulty of setting limit switches to reflect the valve closed position, particularly on gate valves. Although in theory this is straightforward, in practice the build-up of media in the valve or icing in cold climates, can restrict the valve travel. This prevents the tripping of the positions switch and so the control room does not receive the confirming closed signal. This is such a fundamental function of the MOV that it’s surprising it is still an ongoing problem.
Electric valve actuators are generally well regarded by their end users.
But when there are extended contractual chains such as in the valve industry, the manufacturer can sometimes become insulated to the end users experience in the field. There is still some scope for improvement in automated valve design and dialogue with end users can highlight issues that could be eliminated by design improvements.
Published in Valve User Magazine Issue 38
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