ENVIRONMENTAL CONTROL SYSTEMS
LEARNING OBJECTIVES: Explain the role of environmental control systems used in guided-missile launching systems. Identify the major components or systems used in this process.
All GMLSs contain a variety of auxiliary systems that protect the launching equipment and missiles from excessive environmental conditions. Environmental control systems perform the basic functions of heating and cooling. Ship operations in the tropical climates will create high internal magazine temperatures and humidity levels. These conditions affect the reliability of missile propellant grains and play havoc with solidstate electronic control circuits. The colder climates also affect missile propellant performance and launcher component operation. If ice forms around movable guide-arm components, it could feasibly freeze or lock those components in place.
In many cases, the GMLS auxiliary systems rely on the ship's "hotel services" to operate. These services are the responsibility of the ship's engineering department. Steam from the boilers and chilled water from the cooling plants are two such services supplied to our equipment. In such cases, a little interdepartmental cross-training can be valuable.
Every GMLS has some type of auxiliary system that prevents the accumulation of ice formations around critical moving components. One such system is referred to as an anti-icing or circulating system. It is used to circulate a heated fluid throughout the equipments exposed to the weather. Another type of system uses an electrical coil or strip-type heating element to protect the exposed equipment.
Regardless of style, each system has the same end purpose-to melt the ice. Each GMLS also has its own version of an anti-icing system. We will briefly describe atypical system and then point out any unique differences between the GMLSs.
A Typical Anti-Icing System
The typical anti-icing system is an enclosed pressurized fluid system. Its main component is a heat exchanger tank (fig. 8-36). It is normally located in an auxiliary equipment room near the magazine and serves as a reservoir and heater for the anti-icing fluid. This fluid is normally a 50:50 mixture of ethylene glycol and water. The solution is similar to the antifreeze mixture in the radiator of your car.
Inside the heat exchanger tank is a coiled network of steam tubes. They are supplied by ship's auxiliary steam from the main or auxiliary (donkey) boilers. The tubes transfer heat to the anti-icing fluid as it (the fluid) flows through the tank. An air bladder (accumulator)
Figure 8-36.-Anti-icing heat exchanger tank.
inside the tank is charged with low-pressure air. The bladder acts on the fluid to keep a constant pressure in the system. The bladder also compensates for changes in fluid volume caused by temperature variations and minor leakage.
A steam control valve and a temperature-sensing valve monitor and regulate the temperature of the fluid. The sensing valve is installed in the return fluid line of the system and connects to the steam control valve. The sensing valve is adjusted to open and close the steam control valve within a selected temperature range. This action automatically maintains the antiicing fluid within the desired heat range. Although the design specifications of each GMLS will vary, return fluid temperature is generally maintained between 40°F and 60°F. A thermometer is installed in the return line to monitor the temperature of the system.
A small electric motor is used to drive a centrifugal-type pump. The pump draws heated fluid from the tank and discharges it into the system. The supply and return fluid piping networks route the fluid throughout the critical areas of the GMLS. The piping system includes the normal variety of flow control, relief, and air-bleed valves. Strainers and distribution manifolds are also used. In many systems, anti-icing fluid is circulated through special internal passageways drilled or machined in a component.
In addition to circulating heated fluid, anti-icing systems can also run unheated. This optional feature circulates a cool fluid mixture used to help dissipate the heat created by a missile blast.
The anti-icing system in the Mk 26 is also used for missile blast cooling. When blast cooling is selected and a missile is fired, the system starts and runs automatically to circulate anti-icing fluid in the guided-missile launcher, blast door, jettison devices, blowout plates, and platform. The system runs for approximately 10 minutes after the last missile is fired.