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Water is commonly used in ships to provide stability and counteract against uneven loads. Depending on the weight and distribution of the load in the hull, ballast-valve control systems open or close valves to either flood or empty the ballast tanks within a ship’s hull. Known as trimming, it generates counterweights on demand, keeping the ship stable.
Trimming it Up
Traditionally, rotary hydraulic valve actuators have been used to trim operations. Hydraulic actuators are small and powerful, but they require two fluid lines: one for supply and one for return. Plus, with today’s increased environmental awareness, the potential for fluid leaks becomes an issue. Electrical valve actuators could also be used, but ensuring safe operation in these rugged, underwater applications makes them expensive.
Wouter-Jan Hunsche, of Aventics’ Marex Group, explains, “Shipyards want to avoid the expense of installing two runs of tubing for each actuator. At the same time, operators increasingly are adopting the safe and environmentally friendly medium air.”
This application also demonstrates how pneumatics technology can be the most economical solution. Pneumatic tubing and other components are significantly less expensive than their hydraulic counterparts. Hunsche adds, “Shipyards have confirmed a cost advantage of around 30% compared with hydraulics.” Another advantage he cites is that crew members can easily service pneumatic systems on the high seas with tools on board.
Hunsche points out another important requirement of these systems: “The system has to continue functioning if a power failure occurs, even if the valves are completely submerged.” The pneumatic actuators of the Marex Valve Control System (VCS) can be mounted in the ballast tanks and adjusted with no need for electricity. Pneumatic transmission prevents short circuits in the ballast tanks. An active pneumatic position display, the feedback line, sends the valve position to a controller without current, ensuring reliable monitoring.
Depending on the size of the ship, a Marex VCS can work up to 100 ballast and quick-release valves, including air preparation and all necessary operating and control modules. The standard working pressure is 5 to 7 bar, and if a power failure occurs, the crew can generate working pressure using one or more manual pumps.
In the Control Room
Marex AMC operating and control modules can control the ballast-valve control system. This automation system, used extensively in shipping, allows structured access to all ballast-valve control-system information and functions. Furthermore, it groups and displays additional systems, such as the engine, reversing gear, and other functions.
The modular system communicates with the ballast-valve control system via CAN bus. It features a self-explanatory touchscreen controller that mimics the ship’s movements and simplifies operation—a major demand within the shipping industry.
If the main system fails, the valves can be controlled via a backup control and backup system, which are located outside the engine control room. This includes one or more manual pumps that ensure the ability to function in the event of a power outage.
These purely pneumatic actuators function in a wide range of environments: ballast, bilge, and heavy fuel-oil tanks. The Marex systems meet ATEX specifications for all ships and installations with explosive protection requirements.
Hunsche adds that the Marex VCS is certified for use in ships and offshore installations by the world’s leading classification societies. “The system is based on large-scale series components that are available across the globe.”
For more information on Marex and other Aventics products and services, visit www.aventics.us or call (859) 259-3817.
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