SIL3 actuator control valves for safety instrumented systems
Midland-ACS announced that many of its actuator control valve products have undergone third-party assessment to the IEC 61508 functional safety standard, and are now certified to support SIL (safety integrity level) 3 capability. Control valves with this high level of safety integrity are increasingly being specified by process industries to protect personnel and plant, by ensuring fail-safe operation of critical functions such as emergency shutdown. By using SIL3 capable stainless steel valves and actuation controls, designers of safety instrumented systems are able to more easily comply with the risk reduction requirements of the IEC 61508 and 61511 technical safety standards.
As part of the process of attaining IEC 61508 certification, Midland-ACS worked closely with the conformity assessment solutions specialist SIRA. "The certification process is all-embracing," said James Kingham of Midland-ACS. "The first part involved analyzing each valve to component level, evaluating the risk, mode and consequences of failure. The second part comprised a comprehensive audit of company processes, including our engineering, production, quality assurance and sales operations."
He said the company is submitting low service temperature poppet and spool valves, along with further hydraulic products, for assessment.
The first tranche of products to receive SIL3 capability status include direct-acting solenoid and pilot operated poppet valves, pilot operated spool valves, and a number of pilot operated and direct-acting solenoid hydraulic valves for use in ballast control systems. The introduction of such a diverse range of SIL3 capable products provides designers of pneumatic and hydraulic actuation systems with significant configuration flexibility.
All variants of Midland-ACS’ 70 Series direct-acting solenoid 3/2 poppet valves are now certified in accordance with IEC 61508 to have SIL3 support capability. Offering a choice of 1/4, 3/8, and 1/2 in. ports, these valves are designed primarily for actuator control using pneumatic or low-pressure hydraulic media. Two types of solenoid are available, certified to protection classes EExd IIC T6 and T4.
A number of 3/2 body ported poppet valves from Midland-ACS’ 1750 Series now support SIL3 capability. These compact pilot air operated valves feature large flow paths to minimize pressure drop. Certified models include standard temperature service (-20 to 180 C) valves with Viton seals, spanning port sizes from 1/4 to 1-1/2 in., as well as 2- and 3-in. port size valves with Nitrile seals.
The standard temperature service versions of pilot operated 3/2 spool valves from Midland-ACS’ 1500 and 1600 Series also now support SIL3 capability. These Viton-sealed valves offer a choice of 1/4 and 1/2 in. port sizes.
Many Midland-ACS hydraulic valve products for ballast control systems are also now certified for SIL3 capability. These include the DN5, DN10 and DN15 Series pilot-operated valves, as well as the DN3 Series direct-acting solenoid valves. All these designs feature an integral balanced piloting system that enables the low-powered solenoid to switch the valve at high pressures. The DN5, 10 and 15 Series products have metal-to-metal seats, while the DN3 Series employs a ceramic ball and a stainless steel seat. The SIL3 capable version of the DN3 offers a stay-put manual override facility, and is available certified for protection classes ExD IIC T6 and T5.
All Midland-ACS products certified to SIL3 capability are supplied with copies of the Sira certification, which contains all the information that engineers and designers need to calculate the safety integrity level of the complete system, based on its component parts.