Utility Components

Utility Components and System Operation Objective 2a: Without reference, identify basic facts and terms relating to utility components and system operation. A minimum of 11 out of 15 responses must be correct. INTRODUCTION A utility system is defined as a system used in support of another system. An aircraft’s environmental system is an example of a utility system. The C-135’s environmental systems are comprised of a pneumatic system, air conditioning system, cabin pressure control system, and oxygen system. INFORMATION Pneumatic System The pneumatic system delivers hot compressed air (bleed air) from the aircraft engine, quick start APU system (QSAS), or external ground unit and distributes the bleed air for the cabin pressure system, air conditioning (AC), and engine starts. Distribution System and Components DUCT RUNS. A duct run connects each engine and starter to the wing pneumatic manifold and contains components necessary to initially regulate engine bleed air (Figure 2-1).

Each engine has one of each of these four components (Table 2-1). Components Air Check Valve One located at each engine, APU/QSAS, and Ground Service Receptacle. Allow air flow in one direction only and close against reverse flow. Pressure Regulators Spring-loaded, pneumatically actuated valve that maintains bleed air pressure. Pre-Coolers Cools bleed air from the engine using ram air to below 350°F for use in the cabin or air conditioning system. Bleed Air Shutoff Valves Electrically controlled by bleed air switches on the air conditioning panel or by the engine “T” handles. WING PNEUMATIC MANIFOLD. The wing pneumatic manifold (Figure 2-2) extends from left to right across the leading edge of the wing and connects to each engine duct run. BLOW OUT DOORS. The blow out doors (Figure 2-3) are mounted/hinged to the wing leading edge access panels and will open when pressure inside the leading edge panel exceeds outside pressure by approximately 5 PSI.

GROUND SERVICE RECEPTACLE. A single ground service receptacle (located on the left side of the aircraft, forward of the keel beam bays) is provided as a quick connect/disconnect point for an external ground unit (Figure 2-4). APU DELIVERY DUCT. An APU delivery duct is routed from the APU/QSAS along the upper left area of the cargo compartment and delivers bleed air to the wing pneumatic manifold in the center wing equipment bay (Figure 2-5)

BLEED AIR DUCT CROSSOVER VALVE. A bleed air duct crossover valve is located in the center wing equipment bay. It is used to isolate one wing pneumatic manifold from the other in the event of a manifold failure. It is operated by the red guarded Crossover Valve Switch on the AC Panel. Air Conditioning (AC) System The air conditioning system conditions bleed air for heating, cooling (personnel & electrical equipment) and pressurization of the crew and cargo compartments. AC Panel The AC panel is located on the pilot’s overhead panel and contains various indicators and switches for controlling the AC system (Figure 2-6, Table 2-2, Table 2-3) AC MASTER SWITCH is a three-position switch that controls the operation of the AC system. Position AC Master Switch Up (RAM AIR) Opens ram air valve, which is used when emergency ventilation inflight is desired. The aircraft must be depressurized before it is placed in the ram air position. Center (OFF) Both the ram air and AC shutoff valves are closed. Down (COND AIR) Opens the AC shutoff valve allowing bleed air from the pneumatic system to enter the AC system. Table 2-2 AC Master Switch Settings CROSSOVER VALVE SWITCH. The crossover valve switch is a red guarded switch on the AC panel that electrically controls the bleed air duct crossover valve.

AC Control Panel 1. AC Master Switch 4. Cabin Pressure Controller 2. Cross-over valve 5. Manual Control Valve 3. Control Cabin Temperature Selector Figure 2-7 Cargo Compartment Temperature Selector Table 2-3 Switch Placement on AC Control Panel CONTROL CABIN TEMPERATURE SELECTOR. The control cabin temperature selector (Figure 2-6), located on the AC control panel, controls cabin temperature. The temperature has two modes of operation: Automatic and Manual.  AUTOMATIC mode - the temperature regulator automatically maintains a constant selected temperature by varying the opening and closing of the hot air bypass valve.  MANUAL mode - the temperature regulator is bypassed to directly control the hot air bypass valve. The control cabin temperature can be monitored by a temperature indicator located on AC panel that displays temperature in degrees Celsius. Cargo Compartment Temperature Selector A cargo compartment temperature selector on the left forward wall of cargo compartment (Figure 2- 7) provides additional heated air for the cargo and boom operator compartments. Operation is similar to the control cabin temperature selector. AC Shutoff Valve The AC shutoff valve (Figure 2-8) is located in the center wing equipment bay and is controlled by a master switch on the AC panel (Figure 2-6). The AC master switch position controls the valve to allow flow into the AC system or not. If the master switch is placed into the COND AIR position then the valve will open allowing bleed air into the AC system.

Airflow Controller The airflow controller (Figure 2-9), is located in the center wing equipment bay and limits (controls) the volume of bleed air entering the AC system. AC Pack RAM AIR INLET. The ram air inlet (Figure 2-10) is located at the lower left wing root leading edge. The ram air inlet directs ram air across the primary and secondary heat exchangers.

PRIMARY HEAT EXCHANGER. The primary heat exchanger (Figure 2-12), located in the left keel beam bay, is the first stage of cooling pressurized bleed air. It uses ram air (in-flight) or the ground air ejector (on the ground) for cooling air for the AC system. AIR CYCLE MACHINE (ACM). The ACM (Figure 2-12) is a two-part air cooling unit that consists of an expansion turbine directly coupled by a common drive shaft to a compressor. The compressor compresses pre-cooled air leaving the primary heat exchanger and routes it through the secondary heat exchanger. Air leaving the secondary heat exchanger is then directed to the expansion turbine to rapidly expand the air resulting in rapid cooling. Air leaving the expansion turbine, then enters the water separator. SECONDARY HEAT EXCHANGER. The secondary heat exchanger (Figure 2-12), located in the left keel beam bay, cools the air leaving the ACM compressor. It then directs the cooled air back into the ACM expansion turbine for rapid expansion. 35 DEGREE CONTROL VALVE. The 35-degree control valve (Figure 2-11) is located in the duct between the primary heat exchanger and the water separator. The 35-degree control valve opens to allow some of the air leaving the primary heat exchanger to bypass the ACM and secondary heat exchanger to mix with air entering the water separator to prevent freezing. WATER SEPARATOR. The water separator (Figure 2-12) removes moisture from the cooled air leaving the expansion side of the ACM or the 35-degree control valve. The water that is removed is either drained overboard or sprayed into the secondary heat exchanger to aid in cooling.

HOT AIR BYPASS VALVE. The hot air bypass valve (Figure 2-12) in the AC system mixes engine bleed (hot) air and conditioned (cold) air to obtain a desired temperature. The valve is controlled by the control cabin temperature selector on the AC panel (Figure 2-6). GROUND AIR EJECTOR VALVE. There is little to no airflow to cool the heat exchangers on the ground. Therefore, a ground air ejector valve is used to eject engine bleed air at a high velocity out of the ducting. The high velocity air creates a vacuum drawing air through the ram air inlet and over the primary and secondary heat exchangers to aid in cooling for cabin AC. A switch on the left main landing gear torsion link controls the ground air ejector valve. The ground air ejector valve is open when the aircraft is on the ground and automatically closes upon takeoff. Distribution Duct The distribution duct delivers conditioned air to the crew stations and the cargo compartment (Figure 2- 5). Cabin Pressure Control System The pneumatically controlled and operated cabin pressure control system provides a means of maintaining a constant low altitude cabin pressure during high altitude flight. The system responds to a pressure differential between the onboard and outside air pressures. The cabin pressure control system is located on the pilot’s overhead. Components CABIN PRESSURE CONTROLLER. The cabin pressure controller is located on the pilot's overhead panel and automatically maintains a constant selected cabin altitude (Figure 2-13).

MANUAL CONTROL VALVE. The manual control valve (Figure 2-13) is also located on the pilot’s overhead panel. It is used to regulate cabin pressure when the cabin pressure controller is inoperative. OUTFLOW SAFETY VALVES. There are three outflow safety valves (Figure 2-14), one in each main wheel well and one in the nose wheel well. The outflow safety valves respond to inputs from the cabin pressure controller and control cabin pressure by limiting the outflow of air. CABIN PRESSURE WARNING LIGHT. The cabin pressure warning light is located on the copilot’s forward instrument panel. The cabin pressure warning light will illuminate if the cabin pressure is unsafe. EMERGENCY CABIN PRESSURE RELEASE SYSTEM. The emergency cabin pressure release system (Figure 2-15) is manually controlled, which permits rapid depressurization of the aircraft for escape. The release handle is located on the pilot’s center instrument panel and is safety wired with .020 copper wire. The

release handle is connected by a cable to a spring loaded door release assembly to the blow off door. The blow off door is located forward right side of cargo compartment and safety wired with .032 nickel copper wire. Oxygen System The aircraft gaseous oxygen system provides crew members a source of breathable oxygen in emergencies. It consists of a dual gaseous oxygen (GOX) system and a portable oxygen system. Dual GOX System The dual GOX system is located on the cargo deck over the boom operator’s compartment and consists of twelve low-pressure cylinders on a dual rack (Figure 2-16). The primary rack (top row) contains six cylinders and the auxiliary rack (bottom row) contains six cylinders. SERVICING PANEL. A servicing panel (Figure 2-17), located on the lower right side of the fuselage, contains a filler valve, which provides a connection point for the GOX cart and a pressure gauge that indicates the pressure in the distribution system.

AUXILIARY OXYGEN SYSTEM CONTROL PANEL. The auxiliary oxygen system control panel (Figure 2-18) is located between the last two cylinders on the lower right aft side of the oxygen cylinder rack. This control panel has a pressure gauge, which indicates auxiliary system pressure and a filler valve to provide an alternate means of servicing the system. PRIMARY/ AUXILIARY SYSTEM SHUT OFF VALVES. The primary and auxiliary system shutoff valves provide a means of isolating either system from the distribution system. The primary rack isolation/shut-off valve is located on the top forward end of the primary rack and is secured open with .020 copper wire. The auxiliary rack isolation/shut-off valve is located between the last two cylinders on the lower right aft side of the rack and secured closed with .020 copper wire

Aircraft Oxygen Distribution The aircraft oxygen distribution system connects the system servicing valves to the GOX cylinders and delivers oxygen to and from cylinders to the individual regulators and re-charger outlets. REGULATORS. There are nine regulators (Figure 2-19) that receive pressure from the distribution system and deliver oxygen to individual masks. On the regulator panel there is a gauge which read pressure demand with a flow indicator and another which indicates distribution system pressure. The three levers on the regulator control the operation of that specific regulator. The three levers are supply shutoff, diluter lever, and emergency lever. Portable Oxygen Units Eight portable oxygen units (Figure 2-20) provide a mobile or emergency source of oxygen and are used with an oxygen mask. These low-pressure cylinders have a regulator on each bottle. The regulator consists of an oxygen pressure gauge (indicating pressure in the unit) and an altitude selector that controls the rate oxygen is delivered (M=1,000ft). It also provides a covered connection point for the oxygen mask hose. Recharger outlets located in the control cabin, cargo compartment, and boom compartment are used to service the portable oxygen units.