Environmentally Safe Products at Work
For most machine builders, their greatest technical challenge is achieving ever-higher performance (e.g., faster, less scrap, better quality). A segment of Moog's customers face an even greater challenge, how to achieve performance objectives in extreme environments. This article profiles two examples of machinery controlled by Moog's Servovalve and Servo-Proportional Valves that are used in hazardous environments. The first is an offshore oilrig used in the North Sea in a corrosive environment with violent motion and in the presence of gas. Consider the challenges of designing machinery subject to 29-meter (95 ft.) high waves, operating in the extreme temperatures experienced well north of the Arctic Circle.
The second example is a particleboard press system that is exposed to hazardous dust environments that are potentially explosive. This machine is operating around the clock and it requires both high quantity and quality of output. In each case, Moog developed a unique solution that enabled the customer to meet safety requirements required by law as well as the practical performance requirements of a demanding application.
Moog Flame-Proof Servovalves
Following the discovery of significant oil reserves in the North Sea in the late 1960's, a whole industry has been created around developing and building the machinery to find and extract these reserves. A number of Norwegian companies have been very active in supplying equipment to operate on both exploration vessels and offshore platforms in an extremely tough environment. For example, during a storm in the North Sea in 1995 the Draupner Oil Rig was hit by a wave 29 meters (95 ft.) high. The most recent Norwegian offshore field to be developed, Snow White, is located well north of the Arctic Circle.
Machine designers for this equipment have to allow for violent motion, extreme temperatures, a corrosive environment, the presence of gas and increasingly stringent government safety regulations. As a result personnel are no longer permitted on the so-called "drill floor" during operation, meaning that much of the machinery has become highly automated. Often machines moving loads of up to 13 metric tons (28,660 lbs.) have more similarity to giant robot's arms than simple cranes.
Much of this machinery is hydraulic and Moog has been supplying both Servovalves and Servo-Proportional valves since the early 70's. These have been used on a wide range of equipment including pipe handlers, riser tension systems, top compensators, and mechanical roughnecks. Initially these valves were intrinsically safe versions of our standard products but more recently Moog has developed special flame-proof versions of both D63X Direct Drive and D66X High Flow Servo-Proportional Control Valves. These are classified according to the ATEX directive (See Note below) as Ex 2G EEx d IIC: C2H2T5.
The picture shows a group of the flameproof valves supplied to our Norwegian distributor Hydronic A/S for use on a pipe handler. Note the robust housing for the integrated electronics. This is necessary to meet the ATEX directive but it also provides environmental protection permitting the use of standard components in these extreme environments.
Moog Explosion-Proof Direct Drive Servovalves
Particleboard, a form of composition board, is made by binding wood particles together with a suitable adhesive and pressing or extruding them to form sheets. Particleboard is used as a cheaper substitute for plywood in some applications, even though it has a higher density. When properly veneered it is suitable for making furniture. These boards are produced by continuously working Particleboard Press Systems that produce endless pressed boards in consistent high quality. The Continuous Particleboard Press System is the main and most critical operation in the processing plant.
Production of particleboard involves the processing wood particles the size of flakes that also create sawdust. The presence of dust results in a hazardous environment for press systems that is potentially explosive. In addition, such press systems are frequently damaged by fire. Consequently, members of the European particleboard industry and the European regulatory bodies are working on an agreement on how to classify the environment for these machines according to the ATEX Directive (See Note below). It is very likely that the Particleboard Press System will be classified according to the ATEX Directive as Ex II 3 D, which entails that all the hydraulic valves have to be approved as explosion-proof according to this Directive.
ATEX 94/9/EC is the European Directive for equipment intended for use in potentially explosive atmospheres. Directive 94/9/EC is a designed to harmonize directives meaning it will replace existing divergent national and European legislation, which cover the same subjects. For more information, see http://europa.eu.int/comm/enterprise/atex/guide/chapfour.htm#4.4.
A continuous particle press system has 3 main sections, which are electro-hydraulically controlled by Moog Direct Drive Servovalves (D633 and D634 Series)
1. Prepress section - Moog Servovalve supplies position and force control (4 actuators)
2. Main press section - Moog Servovalve supplies position and force control (up to 90 actuators)
3. Edge control section - Moog Servovalve supplies position control (4 actuators)
At the request of a customer, who is seeking the ATEX classification, Moog modified and approved the D633 and D634 series servovalves according ATEX Ex II 3 D, as well as Ex II 2 D (one class higher than required for Particleboard Press Systems).
Moog has an extensive offering of products that are explosion-proof and suitable for a range of environmental hazards including Servovalves, Servo-Proportional valves, Servomotors, Servodrives and electric actuators. Our history of working in the world's most demanding applications means we have vast experience customizing products to ensure that they meet our customer's needs.
In the case of explosion-proof products we also work closely with the appropriate regulatory agencies around the world to help our customers meet all safety requirements as well as their own goals for machine performance. Our global scope also enables us to interface with the requirements in specific part of the world and provide our customers with confidence that wherever the product is sold or used, they have a knowledgeable partner to help.
About the Author
Martyn Waddington has worked for Moog for 38 years in a number of management functions and locations. His current position is Marketing Manager with responsibility for the distribution for Moog industrial hydraulic products in Europe.
Bernhard Zervas has been the Manager, Systems Engineering for Moog's Industrial operations in Germany for 3 years. He has over 30 years experience in the international hydraulic industry, with a focus on industrial electro-hydraulic closed-loop, electro mechanical and hybrid applications.