operate it. Hydraulic SE is used to service and test hydraulic systems and components. To use the equipment, you must understand each piece of hydraulic SE so you can maintain aircraft hydraulic systems. The maintenance and operation of specific SE units are described in applicable manufacturer’s operation and service instructions manual (listed in the NAPI, under "Test Equipment,” 17 series group), and in the maintenance instructions peculiar to the specific aircraft. TYPES OF SUPPORT EQUIPMENT All maintenance levels use SE. General types of hydraulic SE are portable hydraulic test stands, hydraulic fluid dispensing equipment, and stationary hydraulic test stands. Portable Hydraulic Test Stands Portable hydraulic test stands are mobile sources of external hydraulic power. They can be connected to an aircraft hydraulic system to provide power normally obtained from the aircraft hydraulic pumps. The test stands provide a means of energizing the aircraft’s hydraulic systems. SE is used on the flight line and in hanger work areas. In addition, portable test stands are important tools for hydraulic con- tamination control. They are the primary means of aircraft hydraulic decontamination. Several types of portable stands are available. Their primary difference is their prime power source (electric motor or engine driven), functional features, and maximum flow capability. Hydraulic Fluid Dispensing Equipment Hydraulic fluid dispensing units are portable. They are used to replenish hydraulic fluid lost or otherwise removed from a system. They provide a means of dispensing new filtered fluid under pressure, in a manner that minimizes the introduction of external contaminants. Several different types of hydraulic fluid dispensing equipment are available. Stationary Hydraulic Test Stands Stationary hydraulic test stands are permanently installed equipment used for shop-testing hydraulic system components. Except for specialized equip- ment, such as hose burst test stands, they are general-purpose equipment capable of performing a variety of tests on components such as hydraulic pumps, actuators, motors, valves, accumulators, and gauges. Typical component test stands consist of adjustable sources of hydraulic and shaft-driven (for pump drive) power, with associated regulator and indicating devices that let you monitor performance under simulated operating conditions. Stationary hydraulic test stands are used at the intermediate- maintenance level, ashore and afloat, and for depot-level maintenance. CHECKING AIRCRAFT HYDRAULIC FLUID LEVELS There are specific procedures for checking hydraulic fluid levels in each model of aircraft. These procedures must be followed to make sure the system operates at the required fluid level. Fluid level is generally determined by an indicating device at the system reservoir. The type of indicator used varies with the aircraft model. Sight-glass, gauge, and piston-style indicators are commonly used. There is close tolerance between the operating parts of equipment used in aircraft hydraulic systems and the level of hydraulic fluid contamination; therefore, do not introduce foreign matter into a system being serviced. All servicing must be accomplished by qualified personnel using authorized fluid-dispensing equipment. The information contained in this section gives general guidance and requirements to follow when fluid servicing hydraulic systems and components. Remember, you need to follow the procedures contained in the applicable technical manuals when you actually service hydraulic systems and components. When you service these systems, use approved fluid-dispensing equipment that is equipped with 3-micron (absolute) filtration. Maintain equipments according to the applicable MIM and MRC. Keep hydraulic fluid dispensing equipment clean. Store it in a clean, protected environment. Service this equipment on a periodic basis, including filter servicing. Protect all fittings or hose ends with approved metal closures when not in use. Use the correct fluids for each piece of fluid-dispensing equipment, and mark the equipment to indicate the type of fluid. Use the specified hydraulic fluid to service hydraulic systems. Take precautions to avoid accidental use of any other fluid. Do not leave hydraulic fluid in an open container any longer than necessary, particularly in dusty environments. Exposed fluid will readily collect contaminants, which could jeopardize system 4-21