Page 557 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

554 CHAPTER 20 Tooling and Sensor Deployment
FIGURE 20.24
Sub-Atlantic servo valve pack.
configurable digital control system for ROV and tooling applications. The valve pack can be set up in 6, 8, 12, and 16 station versions. In industry vernacular, these types of simple valve packs are often termed “bang-bang” valves as they are typically either fully open or closed (and the valve makes a banging noise as it is opened and closed once the valve hits the stops).
A variation on the general valve pack is the servo or servo-proportional valve pack. These devices convert an analog or digital instruction set into precisely controlled valve movements for smooth operation of hydraulic equipment. This allows movement of multiple actuators simultaneously for accurate control of equipment position, velocity, and force. Tool movements can be much more smoothly controlled with the servo accelerate/stop controls along with dampening capabilities.
Sub-Atlantic’s 8-station servo valve pack is shown in Figure 20.24. The compact servo valve pack weighs 33 lb (15 kg) in seawater and provides precise control of propulsion thrusters on underwater vehicles or can be used to control any tool requiring a variable speed or reversible func- tion. The pack incorporates eight 20 US gpm (77 lpm) rated servo valves that provide low pressure drop on most standard ROV applications.
20.2.4.4 Hydraulic compensators
All oil-filled systems require some type of pressure compensation in order to avoid water intrusion into the hydraulic system from pressure-related volume contraction of entrapped air bubbles as the vehicle descends. Compensation can be provided via flexible covers or specifically designed com- pensators. One manufacturer provides four sizes (270, 370, 860, and 2700 cc) of rolling diaphragm, positive pressure compensators in corrosion-resistant plastic suitable for ROV and tooling applica- tions (Figure 20.25). The range of sizes available is suitable for compensating thrusters, oil-filled junction boxes, valve packs, etc.
(Courtesy Sub-Atlantic.)