Valves need Actuators

Valves and pumps are common components in many plants, but in many ways valve actuators are the antithesis of pumps. Generally, pumps are running virtually all of the time, whilst valve actuators can be inactive for up to 99% of their working life. The only exception is control valve actuation, but even here the activity is rarely continuous.

On an isolating valve the actuator’s function for most of the time is to communicate data about the valve’s position and condition to the controller. However, when asked to change the valve position the actuator must respond with absolute reliability, especially as some valves only open or shut for safety reasons. It is also essential that the actuator communicates a signal to confirm that the requested action is being performed, or sends an alarm if it is not or cannot be completed.

Valves come in a range of designs, each with differing operating requirements for which various valve actuators are available, with a choice of power source encompassing electricity, air or hydraulics. Generally, electric actuation is in the ascendancy for reasons of economy, simplicity and ease of maintenance, although there are industries and applications where fluid power is preferred. For example, electric actuators are designed to stay-put on power failure, leaving the valve in the position to which it was last moved, but there may be important reasons to open or close a valve under these conditions. Because it is easy to equip a pneumatic actuator with a spring that will operate the valve if the power fails, this type of actuator is traditionally specified for such failsafe applications.

Figure 1
Economiser re-circulation pipework at the UK Ratcliffe power station, equipped with failsafe Rotork Skilmatic SL and SHL linear and SQ quarter-turn modulating actuators, together with Rotork IQ range isolating actuators.

Electric actuators can be used, but failsafe operation is usually only possible if a stored energy source such as batteries or an uninterrupted power supply is provided, adding to the cost and complexity. To avoid this problem, the Rotork Skilmatic actuator has been developed to offer spring-operated failsafe benefits with the convenience and cost-effectiveness of electrical operation. The Rotork Skilmatic actuator design incorporates a totally sealed electro-hydraulic power unit with a spring-return actuator. When electric power is applied the hydraulic fluid is pumped to the actuator to operate the valve and compress the failsafe spring, which operates the valve in the reverse direction or in the event of power failure.

The majority of locations for valves, and therefore actuators, are in exposed positions, usually subject to the extremes of the environment, sometimes including flooding. It is therefore essential that the mechanical and, in particular, the electrical components of the actuator are fully protected from the corrosive effects of the atmosphere.

Manufacturers like Rotork have always recognised that environmental sealing is the most important contributor to long-term electric actuator reliability. Rotork introduced ‘double-sealing’ – isolating the terminal compartment from the rest of the actuator’s electrical equipment – as long ago as the 1960’s, and builds virtually all its actuation products to the demanding IP68 watertight and temporarily submersible enclosure specification.

Reliability was further enhanced by the introduction of the ‘non-intrusive’ actuator design, pioneered by the Rotork IQ intelligent actuator range in the early 1990’s. These actuators use a hand held setting tool – rather like a TV programmer – with a secure, dedicated infrared link to the actuator to perform all the switch setting and commissioning functions that were previously only achieved by removing electrical covers. The advantages are significant. Not only is it quick and simple to programme the actuator, it can also be performed in any weather without jeopardising the actuator’s integrity and in hazardous areas with complete safety. Commissioning can also be achieved without the actuator connected to the mains supply.

Now in its second generation, the inherent reliability of the Rotork IQ design has enabled the actuator to incorporate sophisticated electronic control, monitoring and memory functions as standard, all of which are securely contained within the permanently sealed enclosure and are accessible for programming and downloading by the infrared link.

Figure 2
A Rotork engineer ‘non-intrusively’ commissions an IQ intelligent valve actuator at the Scottish Water Daldowie sludge treatment works near Glasgow.

The inclusion of a data logger within the IQ actuator enables an event-by-event history of valve activity to generated, including the torque profiles created by opening and closing the valve. This information can be used to identify potential valve problems before they occur, or to plot a valve wear graph that will predict when maintenance will be required. These abilities enable plant utilisation to be optimised and minimise the risk of disruptive and expensive breakdowns or interruptions.

Figure 3
An IQ actuator data logger screen generated by IQ-Insight software, showing valve torque in the opening and closing directions.

The IQ-Insight software that is used to access, review, analyse and reconfigure the actuator’s set up and data logger information is designed to run on a common PC or laptop, using Microsoft Internet Explorer 4+ or later. Using the infrared link, a laptop can be directly connected to the actuator in the field for set-up, adjustment or analysis purposes; alternatively a PC in a central control room can communicate with the actuator via a modem and cell phone. Settings can be saved and reloaded into the same or another actuator, adding convenience and saving time in many commissioning and fine tuning activities.

Figure 4
IQ-Insight software loaded on a laptop computer is a convenient way of communicating with IQ actuators.

Although these sophisticated electronic monitoring and control features have been developed for Rotork’s electric actuators, the company has also developed derivatives that enable the same benefits of remote control and indication to be applied to the pneumatic and hydraulic actuators built by its Fluid System division. This has the advantage of simplifying the control interface on sites where the different actuator types are used and standardising the information dialogue between site and supervisory system.

The proliferation of data generated by plant equipment such as actuators would be very expensive to transmit to the centralised controller by traditional hard-wired methods. However, the development of two-wire digital bus system protocols has not only solved this particular problem but also enabled more and more useful information to be gathered. Today there is a choice of open systems designed to interface with all the elements of the plant – valves, pumps, flowmeters, level controls etc. – with different industries tending to adopt preferred protocols.

For example, Foundation Fieldbus is popular with the international oil and gas industries and all Rotork actuator designs can be specified with factory-fitted, Foundation Fieldbus cards with a comprehensive list of functions for both monitoring and control. The Rotork Foundation Fieldbus card comprises fourteen digital input, digital output, analogue input, analogue output and PID blocks, in addition to the standard resource and transducer blocks, enabling the actuator to be the controller of complex processes on the Foundation Fieldbus loop.

As well as FF, Rotork offers DeviceNet, Profibus and Modbus connectivity with virtually all of its actuator ranges to meet the preferred requirements of all industries. As a pioneer of digital communication in its own right, Rotork has also developed its own dedicated two-wire control system, known as Pakscan, which has been installed throughout the world on numerous installations, especially in the oil, gas and petroleum industries.

Each Rotork Pakscan master station can operate up to 240 valve actuators, pumps, solenoids, sensors and transmitters on a single loop, creating a data base containing information from each element on the loop. The data is accessed using Modbus protocol and is continuously updated by field unit polling. The master station interfaces with plant supervisory PLC’s or can be operated by a standard PC running Rotork In-Vision software.

Figure 5
A plant overview screen generated by Rotork In-Vision software.

Each In-Vision package is capable of operating plants containing up to 480 Pakscan controlled valves or other devices. In-Vision enables a totally customised, full-colour visual display of the site to be used to monitor and operate the plant using information collected on the Pakscan two-wire control bus.

Figure 6
In-Vision provides individual status screens for every actuator on the Pakscan control loop.

Customisation options include the ability to include the ability to include photographic images on animated screen overviews and close-ups that display general plant conditions. Detailed examinations of chosen plant areas can be performed using enlargements featuring coloured animations to highlight alarms or areas requiring attention. To further facilitate plant operation, every In-Vision system incorporates multiple windows providing status and alarm information and showing the condition of every actuator and master station on the Pakscan system. Audible warnings and action confirmation dialogue boxes can be added to enhance safety where plant controls are critical.

Historical event and alarm data is automatically logged by In-Vision and may be viewed, printed or exported for further analysis on spreadsheets or similar applications. When used with IQ actuators, additional displays may be incorporated to show a graph of torque values as the valve opens or closes. This information is used with historical operating data to maximise plant availability and prepare accurate preventative maintenance schedules.
Rotork Pakscan or the other open two-wire digital control systems are available with all Rotork’s ranges of actuators. With the electric actuators the field units are fitted within the standard actuator enclosure, either in the factory during manufacture or on-site when the plant is being updated.

Fluid System actuators differ from electric actuators in the way that they are built. Generally, the two-wire interface is included in the ‘packaging’ of the actuator which is built to order for a specific contract. The packaging of electrical control equipment, solenoids, switches and manual overrides is very common practice with pneumatic and hydraulic actuators. Rotork, which manufactures its Fluid System actuators in factories in the USA and Italy, therefore complements these facilities with packaging centres of excellence in Canada, Singapore and the UK to service the diverse requirements of its international customers.

The growth of these centres of excellence is evidence of the truly worldwide nature of the industrial valve and actuator market. Rotork supports its products with subsidiary companies, sales and service centres and agencies on every continent, ensuring that even the most remote actuator installation is not beyond the reach of local support. Rotork also recognises the benefits of providing local support, wherever possible, in the language and culture of the end user.

This policy has paid dividends throughout the company’s near-fifty year history. As the international valve actuator market has grown and demand for Rotork’s products has increased, the company has expanded its product ranges and its scope of services to achieve a true ‘one-stop-shop’ status for valve actuation. The product range now includes Rotork electric and Fluid System actuators for valves of virtually every size and configuration, from small factory air lines to massive penstocks and huge, high pressure pipelines. In addition, Rotork Gears has completed its offering of manual and actuated gear operators with the introduction of ranges designed for sub sea applications whilst Rotork Valvekits is a leading manufacturer of valve accessories such as handwheels, chainwheels, switchboxes and actuator adaptation kits.

Finally, whilst the large majority of valve actuators are supplied for new valves, there is also an important market for retrofitting actuators on existing manually operated plants, or replacing obsolete actuators as a part of modernisation programmes. This is another activity that Rotork pioneered in the early 1960’s and now performs internationally. Retrofitting offers a high level of flexibility to the valve end users. It is an economical way of improving plant efficiency and safety or meeting the demands of increasingly stringent legislation. For example, the current introduction of ATEX hazardous area classifications can result in plants requiring improved actuator specifications, or the conversion of emergency shut down valves from manual operation to actuated.

In many cases, retrofit projects include a mix of activities beginning with a survey of existing actuation equipment. This enables a decision to be made about refurbishing rather than replacing some of the actuators, or moving them to alternative duties after they have been replaced, rather than scrapping them. Rotork’ Retrofit’s abilities in these areas enable significant economies to be achieved without any compromise to the overall plant improvement.

Figure 7
Rotork P range quarter-turn failsafe pneumatic actuators installed on the Imperial Oil Resources Ltd Mahkeses Project at Cold Lake Alberta, Canada.