Hydraulic System

Unit 5: Hydraulic Systems Hydraulic Components and System Operation OBJECTIVE 5a: Without reference, identify basic facts and terms relating to hydraulic components and system operation. A minimum of 11 out of 15 responses must be correct.

INTRODUCTION The C-135 has two separate, independent hydraulics systems to move flight control surfaces, landing gear doors as well as provide power to air refueling pumps to quickly off load fuel to many different aircraft. In the following section, you will learn what components each of these systems operates.

The acronym FLIP uses the initial letters of each word to represent the items operated by the left hydraulic system.

The left system operates: • Forward air refueling pumps • Landing gear and landing gear doors • Inboard spoilers • Pilot’s brake system

The acronym RAW BACON CQ uses the initial letters of each word to represent the items operated by the right hydraulic system. The right system operates: • Rudder • Aft air refueling pumps • Wing flap system • Boom • Air refueling receiver (ARR) system (if equipped) • Copilot’s instrument power supply system • Outboard spoilers • Nose steering system • Copilot’s brake system • Quick start APU system (QSAS) (if equipped)

Hydraulic System Components and Operation:

Engine Driven Pumps (4): There is one pump per engine making four total. The engine driven pump is mounted on the accessory gearbox (AGB). The engine driven pumps on the left wing are used to pressurize the left system and the engine driven pumps on the right wing are used to pressurize the right system. The pumps are variable volume, providing up to 22.5 gallons per minute (GPM) per pump

ENGINE DRIVEN PUMP PRESSURE SWITCHES. These switches are installed in the output pressure line of each engine driven pump. These switches are connected to and operate the HYD PUMP INOP lights to indicate low hydraulic pressure.

HYDRAULIC PUMP INOPERATIVE LIGHTS. Four (flashing) amber lights on the copilot’s forward instrument panel indicate low pressure by flashing when a low pressure condition exists in the output pressure line of each engine driven pump (Figure 5-2).]

SHUTOFF VALVE. The shutoff valves, shut off fluid flow to engine driven pumps. The shutoff valves are located in the outboard dry bays in the supply line to the engine driven pumps. The shutoff valves are controlled by the engine “T” handles on the glare shield, or by the red guarded hydraulic pump supply switches on copilot’s forward instrument panel

Electrically Driven Auxiliary Hydraulic Pumps In addition to the engine driven pumps, each system contains one electrically driven auxiliary hydraulic pump, located in each wing fillet area (Figure 5-4) to supply pressure to the left and right hydraulic systems. The left auxiliary pump is in the left wing fillet area and the right auxiliary pump is in the right wing fillet area. The pumps provide a means of pressurizing the hydraulic systems without operating an engine during ground maintenance. The auxiliary pumps are capable of delivering 0.71 GPM at 3,000 PSI. They can also be used to provide fluid under pressure for in-flight emergencies (IFEs). Figure 5-4 Aux. Hydraulic Pump ELECTRICALLY DRIVEN AUXILIARY HYDRAULIC PUMP PRESSURE SWITCHES. Electrically Driven Auxiliary Hydraulic pump pressure switches are installed in each auxiliary pump pressure line (located in the respective wing fillet area) to control auxiliary pump operation when the auxiliary pump control switch is in the AUTO position.

Hydraulic Control Panel Hydraulic Control Panel The hydraulic control panel is located on the pilot’s side panel and it contains switches and gauges for each hydraulic system. The left and right hydraulic pressure switches (upper two) are self-locking, two position switches that control the position of the depressurization valve. ON (up) closes the depressurization valve to allow system pressure to build-up. OFF (down) opens the depressurization valve to relieve system pressure through the return line, to the reservoir (Figure 5-5). While the bottom two switches on the control panel are known as the pump control switches. The pump control switches are separated into left and right and provide different functions as seen below (Table 5-1). Aux pump control switches Left Right Up position Auto: Energizes the left aux pump Auto: Energizes the right aux pump Center position Off: De-energizes the left aux pump Off: De-energizes the right aux pump Down position (Spring loaded to off) Reserve brake: Builds pressure in pilots reserve brake accumulator On: Builds pressure in the right hydraulic system accumulator when held down. Table 5-1 • Brake pressure is used to set brakes during normal towing operations. • Aux pump control switches receive power from the switched DC bus.

DIRECT READING GAUGES. On the hydraulic control panel there are three direct reading pressure gauges. The gauges will indicate hydraulic system pressure that exceeds the pre-charge of its respective accumulator. The gauges are listed as follows (as installed on aircraft): • Left (aft) gauge - indicates left system hydraulic pressure. • Center gauge - indicates right system hydraulic pressure. • Right (forward) gauge - indicates the pilot’s reserve brake system pressure. These gauges are connected to and reflect the pre-charge of each respective accumulator, when the systems are depressurized (Figure 5-6). Figure 5-6 Direct Reading Gauges

Depressurization Valve Located in each respective wing fillet area (Table 5-2) (Figure 5-7), the left and right hydraulic systems incorporate an electrically operated valve, which is controlled by the system hydraulic pressure switches located on hydraulic control panel (Figure 5-5). This valve provides the means of pressurizing and depressurizing the systems. Depressurization control switches Left Right Up (on) Left depressurization valve closed to build pressure Right depressurization valve closed to build pressure Down (off) Left depressurization valve open to relieve pressure Right depressurization valve open to relieve pressure Note: Relieved pressure is returned to respective reservoirs. Table 5-2 Depressurization Control Switches

Brake Hydraulic Accumulator Selector Valve The brake hydraulic accumulator selector valve is mounted in the left wing fillet area (Figure 5-8). It directs pressure to either the reserve brake accumulator exclusively or the left hydraulic system including the reserve brake accumulator. It all depends on the position of the left auxiliary hydraulic pump control switch. With the left auxiliary hydraulic pump control switch in RESERVE BRAKE, only the reserve brake accumulator receives pressure. With the left auxiliary pump control switch in AUTO, the reserve brake accumulator and all of the other left system components receive pressure.

Hydraulic System Pressure Relief Valve The left, right, and reserve brake system each have a hydraulic system pressure relief valve to protect the system against the damage caused by abnormally high pressure. The valves relieve excess system pressure back to the reservoir. The valves are set to relieve pressure at 3,500 PSI (Figure 5-9).

Accumulators There are up to eight accumulators installed on the KC-135 R model aircraft. Accumulators protect the hydraulic components against sudden pressure surges and store a supply of pressurized fluid for emergency use. Accumulators are pre-charged with nitrogen (Figure 5-10) (Table 5-3).

Total Accumulator Location 1 Left system Left wing fillet area 2 Right system Right wing fillet area 3 Reserve brake Forward bulk head of left wheel well 4 Boom Boom sighting door area 5 Rudder Tail compartment 6 QSAS APU 1 QSAS control cabinet 7 QSAS APU 2 QSAS control cabinet 8 ARR Control ceiling (If equipped)

Spoiler Hydraulic Pressure Cut Out Switches The left and right spoiler bypass valves are controlled by red guarded spoiler hydraulic pressure cut out switches that are located under the glare shield. The left switch controls the inboard spoilers, while the right switch controls the outboard spoilers

Power Rudder Switch Located on the control stand between pilot and copilot’s seat is the power rudder switch. This red guarded switch controls the source of power (hydraulically or manual) (Figure 5-12). • Switch guard is opened and switch is placed in OFF position during right hydraulic system pressurization. • Switch returned to ON position and guard is closed during right hydraulic system depressurization. Figure 5-12 Power

Rudder Switch Rudder Hydraulic System Gauge The rudder hydraulic pressure gauge is mounted on the lower left corner of the pilot’s forward instrument panel and indicates rudder hydraulic system pressure when the power rudder switch is in the ON position (Figure 5-13). Figure 5-13 Rudder System Gauge CUI CUI BLOCK V SG J3ABR2A534A018D 41

Reservoir Hydraulic fluid is supplied from two 5.0 gallon capacity reservoirs. There is one reservoir for the left system and one for the right. The reservoirs are installed in the outboard dry bay of each wing (Figure 5-14). The reservoir is serviced through an access panel in the upper surface of the wing. Prior to checking level of reservoir the following items must be accomplished: • The system must be depressurized. • The accumulators must have proper pre-charges. Figure 5-14 Reservoir Figure 5-15 Regulator RESERVOIR AIR PRESSURE REGULATOR. A pressure regulator is installed in the engine bleed air line upstream of each reservoir to regulate engine bleed air pressure in the reservoir and assist fluid flow to the pumps. The regulator is mounted in the outboard dry bay adjacent to the reservoir (Figure 5-15). RESERVOIR QUANTITY GAUGE. This dual pointer quantity gauge on the copilot’s forward instrument panel electrically indicates the quantity of hydraulic fluid in each system’s reservoir. Gauge markings are from E (empty) through 5.5 gallons. The gauge indicates up to 5.5 gallons for the air pressure, which assists the flow of fluid (Figure 5-16). Figure 5-16 Quantity Gauge CUI CUI BLOCK V SG J3ABR2A534A018D 42 Hydraulic Filters Hydraulic filters are incorporated to remove any foreign material or objects that may enter the hydraulic system lines. There are a total of six pressure filters for both hydraulic systems and two return line filters for each respective reservoir. Eight filters total (Figure 5-17). • #1-4 engine driven pump (Installed in the output pressure lines) • Left system auxiliary pump (Installed in the output pressure line) • Right system auxiliary pump (Installed in the output pressure line) • Left system reservoir (Installed in the return line) • Right system reservoir (Installed in the return line) Figure 5-17 Hydraulic Filters Hydraulic Crossover Valve A manually operated hydraulic crossover valve provides a means of selecting either the left or right hydraulic system to operate essential components during a system malfunction. This hydraulic crossover valve is used in emergency situations in flight to help get the aircraft home. The hydraulic crossover valve itself is mounted on the inboard wall of the right main wheel well (Figure 5-18) and is controlled by a handle above the copilot’s position (Figure 5-19). The three positions on the handle are as follows: • RH: Adds landing gear to the right hydraulic system. • Normal: left and right hydraulic systems operate normally. • LH: Adds Flaps, Boom, Rudder, and QSAS to the left system.