Penny + Giles has supplied its ICS100 linear potentiometers to provide positional feedback for Xylem Flow Control’s range of electro-hydraulic actuators, which provide a solution for the operation of choke and control valves used in the oil and gas industry; and for water & wastewater transport and treatment applications.
Xylem has worked closely with Penny + Giles for over twenty years since specifying the company’s HLP100: predecessor of the current ICS100 potentiometer fitted to Xylem’s range of electro-hydraulic actuators.
As Xylem’s engineer John Smallshaw explains: “We specialise in the design and manufacture of electro-hydraulic actuation for control valves for both onshore oil and gas pipelines and pumping stations and offshore topside choke pressure and flow control applications, where there is either Zone 0 (constant hazard) or Zone 1 (occasional hazard) risk from explosive petrochemical gas.
“A typical application is to provide an actuator control system to meet the operating parameters of the specified size of valve based on the working stroke, the fail action and operating thrusts for opening and closing the valve against process operating conditions. The process valve must be capable of handling the specified pressure or volume of oil or gas determined by the valve manufacturer, and the actuator is sized to meet the operating conditions for that particular application. It is our decision to select the position feedback device that will provide optimum accuracy and performance for the system.” he says.
As an example, for Zone 0 applications Xylem would normally use a potentiometer or an alternative intrinsically-safe certified device. The potentiometer is invariably the easiest and most cost-effective device to apply, however the selection of the feedback device may be determined by the hydraulic operating fluid as the position feedback device is of the ‘in-cylinder’ type and therefore immersed in hydraulic fluid.
The company prefers to work with mineral-based hydraulic fluids as they are generally suitable for use with potentiometers. For systems incorporating water-based fluids such as water glycol, special consideration has to be given to the selection of the feedback device or the method of mounting the potentiometer. It is possible to locate the potentiometer within a special oil chamber that is mechanically linked to the actuator but operating outside the hydraulic medium.
Xylem uses Penny + Giles in-cylinder devices, which is why it is predominantly the ICS100 that is installed in the back of its hydraulic actuators. Linear actuating devices are used on linear choke and plug valves rather than rotary units because potentiometers provide an intrinsically safe feedback signal from a relatively low power source. Equally important for safety reasons, unlike inductive feedback devices, potentiometers aren’t capable of producing a current to generate a spark.
Typical applications include valve systems installed topside on oil and gas production platforms, helping to control the flow of media as it is being transferred up through the special risers that transport media from the well itself; and on to the pipelines that eventually transport it ashore for storage or processing. Automatic feedback from the potentiometer, delivered via a closed-loop system, allows pressure and flow to be monitored and analysed and the position of the valve adjusted as required.
A nominal 5 volt signal is supplied to the ICS100 from the Xylem positioner controller, which operates on an input signal from a control panel to tell what valve adjustments are needed to maintain the required flow or pressure – 4 milliamps signal is the closed position and the signals between 4 and 20 milliamps represent 0-100%. So if the valve receives a 12 milliamp signal it will recognise the change in voltage as its new 50% position, based on feedback from the Penny + Giles potentiometer.
Plug and globe valves are normally modulating as they respond to changing process conditions caused by flow and pressure variations. However, choke valves fitted topside of the wellhead to control the flow/pressure of media coming out may remain in one position for extended periods and only change as the oil or gas pressure in the well depletes in order to allow flow to be maintained.
Xylem has actuators operating within onshore oil and gas pipelines in Turkey, India and, most recently, a crude oil pipeline in Abu Dhabi. They are also used to control valves in pumping stations, where the oil and gas is compressed and re-charged to enable it to be transported through the pipeline. For these applications ICS100 potentiometers are fitted to the actuators to provide the feedback that monitors pressure and flow control valves.
Summing up, John Smallshaw says the migration from Penny + Giles’ HLP100 to the new, metric ICS100 was virtually seamless as the models are interchangeable; so when he needs to replace HLPs or supply spares, even after all this time, it is natural to specify the ICS.
He adds: “In-cylinder potentiometers play a crucial role in our actuator business in terms of performance, reliability, safety and value, which is why we buy Penny + Giles. The ICS100 is very easy to specify and install, it is competitively priced and the company listens to our input and responds quickly to any issues we have.”