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All components protected in one housing

Electrohydraulic valve actuator
All components protected in one housing

Powerful, reliable and simple valve control with integrated safety functions plays a decisive role for the smooth operation of complex plants in the chemical process industry. Hoerbiger has developed the Trivax electrohydraulic valve actuator based on these requirements. While conventional valve actuators generally consist of entirely separate technologies – mechanics, electronics and hydraulics – the Trivax combines all the components protected in a compact housing.

The author: Marcus Grödl Head of the Business Unit Valve Automation, Hoerbiger

Automated control valves are the heart of every process system: they control pressurised liquid or gaseous substance flows and ensure that chemicals and gases reach the right location at the right time. The reliability of these key components is a main area of concern for ensuring efficient operation of the plants. As a result, the control valves must operate safely over many years in production environments that are at times subject to extreme conditions in terms of temperature, pollution, material stress and maximum availability. All of these are dependent upon high power density, combined with the simple integration of safety functions. While conventional valve actuators generally consist of entirely separate technologies – mechanics, electronics and hydraulics – Hoerbigers’s system combines all the components protected in a compact housing. “Tri” in Trivax denotes the three technologies – mechanics, electronics and hydraulics – that are blended, with “vax” being the acronym for valve actuator.
The electrohydraulic valve actuator combines the advantages of hydraulic systems with the ease of installation and handling of electric valve actuators, especially for applications in the chemical industry. Unlike an all-electric drive system, this electrohydraulic design offers extensive power and torque reserves thanks to the integrated hydraulics, and is powerful and durable – yet has a comparatively low power input. This durability results in minimised maintenance as compared to conventional hydraulic valve actuators. The Trivax is equipped with an intelligent electronics system to efficiently and safely operate the process plants, and it offers numerous diagnostic and special functions to support the operator.
At the same time, its compact closed design eliminates the common weaknesses of hydraulic actuators, such as leakage and failures caused by contamination. The piping-free design assures this singular reliability, because leaks are systematically prevented. It has ultimately extended the maintenance interval of the drive system to five years. The flame-proof encapsulated housing sets new standards for safe use in extreme environments and areas prone to explosions – specifically for Ex protection according to ATEX II2GB Ex d IIB T4. The hermetic encapsulation eliminates the need for separate explosion protection of the individual components that was customary in the past. In addition, decisive factors when selecting an actuator in the process industry include specific safety features such as “Emergency Shutdown“ or ”Quick Action“, allowing actuators to completely close within fractions of a second. The Trivax valve actuator is equipped with this feature, whereby the actuating time can be set to less than one second.
Locally or remotely
The integrated electronic system allows the actuator to be locally controlled using the graphic user interface as well as remotely actuated via the control centre using analogue or digital control signals with programmable feedback options. Interfaces with standard field bus systems make it possible for the Trivax to be integrated into both new and existing automation concepts. The electronic user interface displays information about the drive position and the state of the final control element, provides intuitive communication and controls the drive. The invokable and controllable functions are supported with plain text messages in various languages and allow easy control and programming of the drive system, without the need for opening the housing or removing covers.
Easy installation
Easy installation, as we know it today from electric valve actuators, is made possible by the consistent reduction of interfaces. The Trivax has only one mechanical interface to the valve and an electrical interface to the process control system. The central hydraulic power units required for conventional hydraulic systems, featuring large tanks, accumulator elements and related piping, have been completely eliminated. Given the easy installation, which requires only the supply of electrical power and electrical control signals, the electrohydraulic valve actuator from Hoerbiger is particularly well-suited for the automation of remotely located valves.
The piping-free design prevents leakage on pipe connections. Leak-free and reliable operation is assured by the modules being mounted directly on each other, to include the drive system, within a housing. In addition, the encapsulated, closed construction protects the components inside from a wide range of environmental factors such as corrosion. The problem of internal and external leakage typical of hydraulic final control elements is elimi-nated, and the energy stored in the hydraulic accumulator is not lost over time. This guarantees a consistent position of the valve during operation. Because of the decentralised concept, hydraulic energy is generated only on demand, which lowers operating times and lessens the degradation of the hydraulic fluid. This low degradation allows for maintenance-free operation.
The valve actuators are designed for applications with torque up to 64 kNm for part-turn actuators or up to 360 kN of force for linear drives. The dimensions of 840 x 320 x 600 mm for a double-acting linear drive with a maximum force of 70 kN and travel of 220 mm are smaller than those of electrical actuators for similar forces.
Valve control in power plants
Chemical parks, where several companies are colocated, often have their own power supply plants. For cost reasons, these power plants are frequently designed as combined cycle (CC) power plants with maximum efficiency. It goes without saying that the plant operators within a chemical park rely on a powerful and continuously available power supply. With its Trivax electrohydraulic valve actuator, Hoerbiger covers an important detail for uninterrupted supply. Several of these valve control units have already been successfully employed in CC power plants in chemical parks in Germany and Scandinavia.
Such power plants obtain the required energy from high-performance gas turbines, which are operated with preheated natural gas. A water-natural-gas heat exchanger stores thermal energy, releasing it to the natural gas for preheating. This heated natural gas ensures optimal conditions for natural gas combustion. A quick-acting gate valve is installed in the water circuit to protect the sensitive components in this circuit from a sudden interruption in service. This valve must close with response times of less than one second in the event that a defined target temperature of the water is exceeded, because all the components of the water-natural-gas heat exchanger are designed for this temperature. Any time temperatures are exceeded, for example because of a defective control unit, there is a risk of permanent damage and failure of the entire power supply.
The quick-acting gate valve was complex and expensive to install, and installation in the immediate vicinity of the heat exchanger was not possible. Conventional hydraulic valve actuators often have no explosion protection feature. The valve could therefore only be installed outside the areas of the heat exchanger to which natural gas would be supplied, which necessitated additional piping for the hydraulic system. Finally, it had to be taken into consideration that the valve actuator had to be encased in a weather-proof housing because of the outdoor installation to prevent damage from corrosion. The electrohydraulic valve actuators met all these requirements. The purely electrically controlled hydraulic actuator is designed and mounted so that the user is provided with a hermetically sealed and explosion-protected valve actuator with all the Atex certifications.
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