Artist’s rendering of offshore oil drilling platform using Moog ATEX Digital Interface Valve and Manifold.

In the oil and gas industry, design engineers use servo valves for flow and pressure control with hydraulic motors. To meet the rugged requirements for oil and gas drilling, engineers are designing servo valves with onboard microprocessing. These valves combine rugged construction with fieldbus functionality to offer machine builders around the world the ability to communicate seamlessly with other fieldbus devices and obtain advanced functionality and system diagnostics. With the correct servo valve, a design engineer can eliminate the need for separate flow and pressure control valves. This reduces the complexity of hardware on a drilling platform, which means quicker start-up, easier troubleshooting and simplified maintenance.

ATEX-certified valves for oil and gas drilling

The term ATEX (which comes from a European Union directive describing the kind of equipment allowed in an explosive atmosphere) applies to a work environment like an oil platform where the presence of dust vapour or gases may ignite or explode. There are a range of certifications required for products used where fire or explosion hazards exist due to the presence of flammable gases or vapours, and flammable liquids. ATEX is a global certification for products such as servo valves that are used in these environments and it is typically required by companies that sell into the European Union.

A range of levels is defined by the regulations (e.g., II 2G Ex d e IIC T6/T5/T4/T3 Gb) and machine builders together with maintenance staff look for technologies that can obtain the performance needed to ensure compliance with these regulations. To ensure servo valves can withstand high vibration, engineers must also complete the qualification for vibration transmission and test a valve (according to DIN EN 60068-2-6) with a specific sinusoidal vibration across a hertz range in all axes. ATEX-certified servo valves meet the safety requirements for explosive gas atmospheres.

The application and its challenges

To better understand how an ATEX Digital Valve can benefit a machine builder, we examined an application with a major energy systems company looking to improve the way its employees control a large hydraulic motor in a drilling subsystem.

Although the pressure and flow rates were easily achieved at 210 bar (3,000 psi) and 190 lpm (50 gpm) respectively, the drilling environment is demanding (heavy use, constant vibration and the potential to release underground gas pockets).

Initially, the energy systems company’s request was for advanced flow control to dynamically control the hydraulic motor speed with minimal pressure drop and to reduce piping connections. While working with the customer’s engineers, we learned that future systems could benefit from pressure control that would allow repeatable output torque at slow speed.

Greater functionality drives new opportunities

Our solution consisted of the single stage ATEX Digital Interface Valve with a unique 4-way spool configuration and a custom manifold package, consolidated piping connections with mounting for the servo valve, a solenoid valve, backpressure valve and a drainable pressure filter.

In the ATEX Valve, sensors coupled to onboard electronics provide closed-loop control for both flow and pressure, which correlate to highly accurate control of speed, torque, position and force. In the past, only pressure or flow control was possible with explosion-proof valves. With the ATEX Valve, the energy company can now control both pressure and flow with a single valve, offering machine builders a way to simplify motion control and maintenance.

The application evolved over time as more functionality of the digital valve was used. Initial models provided proportional flow control with a 4-20 mA analogue interface. Later configurations used more advanced valve features with combined flow and pressure control (pQ control) and the Profibus-DP® fieldbus interface. The pQ-configured valve is capable of closed-loop speed control through the hydraulic motor’s encoder and closed-loop pressure control through a pressure sensor within the valve for active control of the motor’s output torque.

The manifold package and internal passages were modelled in 3D, which we used for fluid velocity and internal stress validation to ensure we could maintain calculated pressure drops and a 4-to-1 factor of safety. Once validated, the customer directly imported the detailed, solid model into their higher-level system schematics.

How does the ATEX Div work?

We completely integrated control electronics within the ATEX Valve, incorporating a microprocessor-based system for executing all key functions via embedded software. This offers flexibility for the valve to adapt to a wide range of operating conditions, while maintaining a high level of accuracy and repeatability. In particular, it enables highly optimised system performance even with significant variations in pressure and temperature.

2. With an easy adjustment to 1 or 2 set points, the setting time and amount of overshoot can be changed to quickly meet the application requirements for no overshoot.

Since a customer may download control parameters using the fieldbus or a high level PLC programme, operators can tune the valve control function during the machine operating cycle. Integrated continuous monitoring of a range of important valve and system functions and remote diagnostics are possible.

With an electrically isolated fieldbus interface, operators can change valve parameters on site or remotely. The built-in fieldbus interface (e.g., CANopen®, Profibus-DP® or EtherCAT®) enables adjustment of operating parameters, controlling the valve and monitoring of performance. In a safe, private or virtually private network, the energy systems company we worked with could communicate directly with the valve from anywhere in the world. These valves are also available in a version without a fieldbus interface that is controlled using analogue inputs and includes a service connector for setting parameters.

3. Hydraulic Motor Control package includes Moog DCV Valve with on-board digital electronics.

To reduce downtime due to installation and maintenance, we incorporated a unique feature in the ATEX Digital Interface Valve Series called hot plugged connector capability. This enables the user to connect and disconnect the valve with the electrical supply switched on. These connectors meet the demands of shock and vibration. For use in rough environments like offshore applications, all provided power and data cables are mud-protected.

The result

We completed initial builds of the system in 16 weeks from date of order with integration during start-up. The new version of the valve configuration software helped make setup, diagnostics and tuning easier for the energy services company. The initial application has led to projects in areas where customers did not typically use proportional control.

4. ATEX-certified Digital Interface Valves.

The ATEX Digital Interface Valve series is available in sizes 03 and 05 (according to ISO 4401) and pilot operated valves are available in sizes 05 to 10 and the maximum operating pressure is 350 bar (5,000 psi).

The valves are certified according to ATEX guideline II 2G Ex d e IIC T6/T5/T4/T3 Gb, which defines various environmental conditions of the locations where customers can use the product. The products can operate reliably in a range of -20 to +60 °C (-4 to +140 °F) for ambient temperature and -20 to +80 °C (-4 to +176 °F) fluid temperature. These temperature ranges depend on certified temperature classes according to ATEX. Applications for low temperatures down to -40 °C (-40 °F) are also available upon request. The IP protection class is IP66. 

About the Authors.

Thomas Röhlig started at Moog GmbH in 2006 as Development Engineer for hydraulic pumps, with responsibility for mechanical design and construction. Mid 2009 the field of responsibility for mechanical design and construction has expanded to servo and proportional valves. He studied Mechanical Engineering at the University of Applied Sciences in Jena, Germany.

Kevin Kolmetz started at Moog in 2011 as Product Sales Manager for the Topside Oil & Gas Market. Kevin has spent 11 years supporting electro-hydraulic & pneumatic actuation needs of customers in the aerospace, defence & industrial markets. He earned degrees in mechanical engineering and new product development from Rochester Institute of Technology, Rochester, NY USA.

Thomas Röhlig, Development Engineer,

Moog GmbH, thomas.rohlig@moog.com

Kevin Kolmetz, Product Sales Manager,

Moog Inc., kevin.kolmetz@moog.com