APU/Hydraulics

Description

Auxiliary Power Unit Image

Fuel System

Fuel Tanks

Auxiliary Power Unit Locations

APU Meters and Switches on Panel F8

Improved APU Fuel System Schematic

APU Fuel TK VLV Switches and Circuit Breakers on Panel R2

Fuel Tank Isolation Valves

Fuel Pump

APU Information on BFS SM SYS SUMM 2 Display

Fuel Control Valves

Gas Generator and Turbine

Lubricating Oil

APU OIL TEMP Meter and Switch on Panel F8

Electronic Controller

APU Start

APU Speed Control

APU Auto Shutdown

APU Ready-for-Start Talkback Indicator Logic

APU/HYD Ready to Start Talkbacks on Panel R2

APU Operate Switches on Panel R2

APU Speed Select Switches on Panel R2

APU AUTO Shut Down Switches on Panel R2

APU Overspeed/Underspeed Detection

Injector Cooling System

APU Injector Cooling

Fuel Pump and Gas Generator Valve Module Cooling

APU Heaters

APU Heater Controls on Panel A12

Water Spray Boilers

Nitrogen Supply System

Water Spray Boilers

Water Spray Boiler Unit

SM APU/HYD Display (DISP 86)

Water Spray Boiler

Water Supply System

Boiler Switches on Panel R2

Temperature Control

APU FUEL/H2O QTY Meter and Switch on Panel F8

Heaters

Main Hydraulic Pump

HYD MAIN PUMP PRESS 1,2,3 Switches on Panel R2

Hydraulic System Schematic

HYDRAULIC PRESSURE and QUANTITY Meters on Panel F8

Hydraulic Reservoir

Hydraulic Accumulator

Circulation Pump and Heat Exchanger

BFS SM SUMM 2 Display

HYD CIRC PUMP Switches on Panel R2

Hydraulic System Controls on Panel A12

SM HYD THERMAL Display (DISP 87)

Hydraulic Heaters

Operations

APU/HYD Caution and Warning Summary

APU/HYD Caution and Warning Lights on Panel F7

APU/HYD Summary Data

APU/HYD Rules of Thumb

APU/Hydraulic Overview

Panel R2

Panel F8

Panel 12

DISP 79 SM SYS SUMM 2 Display (PASS and BFS)

SM HYD Thermal Display (PASS DISP 87)

SM APU/HYD Display (PASS DISP 86)

APU/Environ Therm (PASS DISP 88)

Auxiliary Power Unit Image

Description

The orbiter has three independent hydraulic systems. Each consists of a main hydraulic pump, hydraulic reservoir, hydraulic bootstrap accumulator, hydraulic filters, control valves, hydraulic/Freon heat exchanger, electrical circulation pump, and electrical heaters.

Each system provides hydraulic pressure to position hydraulic actuators for:

1. Thrust vector control of the main engines by gimbaling the three SSMEs

2. Actuation of various control valves on the SSMEs

3. Movement of the orbiter aerosurfaces (elevons, body flap, rudder/speed brake)

4. Retraction of the external tank/orbiter 17-inch liquid oxygen and liquid hydrogen disconnect umbilicals within the orbiter at external tank jettison

5. Main/nose landing gear deployment (system 1)/(system 1 or 2)

6. Main landing gear brakes and anti-skid

7. Nose wheel steering (system 1 with backup from system 2).

Each hydraulic system is capable of operation when exposed to forces or conditions caused by acceleration, deceleration, normal gravity, zero gravity, hard vacuum, and temperatures encountered during on-orbit dormant conditions.

Three identical, but independent, improved auxiliary power units (APUs; also called IAPUs) provide power for the orbiter hydraulic systems. The APU is a hydrazine-fueled, turbine-driven power unit that generates mechanical shaft power to drive a hydraulic pump that produces pressure for the orbiter’s hydraulic system. Each unit weighs approximately 88 pounds and produces 135 horsepower.

Each APU consists of a fuel tank, a fuel feed system, a system controller, an exhaust duct, lube oil cooling system, and fuel/lube oil vents and drains. Redundant electrical heater systems and insulation thermally control the system above 45° F to prevent fuel from freezing and to maintain required lubricating oil viscosity. Insulation is used on components containing hydrazine, lube oil, or water to minimize electrical heater power requirements and to keep high surface temperatures within safe limits on the turbine and exhaust ducts.

The three APUs and fuel systems are located in the aft fuselage. Each APU fuel system supplies storable liquid hydrazine fuel to its respective fuel pump, gas generator valve module, and gas generator, which decomposes the fuel through catalytic action. The resultant hot gas drives a single-stage, dual pass turbine. The turbine exhaust flow returns over the exterior of the gas generator, cooling it, and is then directed overboard through an exhaust duct at the upper portion of the aft fuselage near the vertical stabilizer.

The turbine assembly provides mechanical power through a shaft to drive reduction gears in the gearbox. The gearbox drives a fuel pump, a hydraulic pump, and a lube oil pump. The hydraulic pump supplies pressure to the hydraulic system. The fuel pump increases the fuel pressure at its outlet to sustain pressurized fuel to the gas generator valve module and gas generator. The lube oil system supplies lubricant to the gearbox reduction gears and uses the reduction gears as scavenger pumps to supply lube oil to the inlet of the lube oil pump to increase the pressure of the lube oil system.

The lube oil of each APU is circulated through a heat exchanger in a corresponding water spray boiler. Three water spray boilers (WSBs), one for each APU, cool the lube oil systems. The hydraulic fluid of each hydraulic pump driven by an APU is also circulated through a hydraulic heat exchanger in the corresponding water spray boiler to cool hydraulic fluid during hydraulic system operation. The three WSBs are also located in the aft fuselage of the orbiter.

Fuel System

The APU fuel system (one for each of the three APUs) includes the fuel tank and fuel isolation valves, the fuel pump, and fuel control valves. The improved APUs use passive heat sinks and heat shields to minimize the effects of heat soakback.

Fuel Tanks

The APU fuel tanks are mounted on supports cantilevered from the sides of the internal portion of the aft fuselage. The fuel is storable liquid anhydrous hydrazine. The hydrazine is stored in a fuel tank with a total capacity of about 350 pounds. The fuel tank, which incorporates a diaphragm at its center, is serviced with fuel on one side and the pressurant (gaseous nitrogen) on the other. The nitrogen is the force acting on the diaphragm (positive expulsion) to expel the fuel from the tank to the fuel distribution lines and maintain a positive fuel supply to the APU throughout its operation. Each typical prelaunch fuel tank load is approximately 325 pounds. The fuel supply supports the nominal power unit operating time of 90 minutes in a mission or any defined abort mode, such as an abort once around, when the APUs run continuously for approximately 110 minutes. Under operating load conditions, an APU consumes approximately 3 to 3.5 pounds of fuel per minute.

Auxiliary Power Unit Locations

 

The fuel tanks are 28-inch-diameter spheres. Fuel tanks 1 and 2 are located on the port side of the orbiter’s aft fuselage, and tank 3 is located on the starboard side. Each fuel tank is serviced through its respective fill and drain service connections, located on the corresponding side of the aft fuselage. The gaseous nitrogen servicing connection for each fuel tank is located on the same panel as the fuel servicing connections on the corresponding side of the aft fuselage. The fuel tank is pressurized to 365 psi prelaunch.

Each fuel tank’s temperature and gaseous nitrogen pressure are monitored by the APU controller and transmitted to the GPC, where quantity is calculated and transmitted to the APU FUEL/H2O QTY meters on panel F8. When the switch below the meters on panel F8 is positioned to FUEL, the quantity in APU fuel tanks 1, 2, and 3 is displayed simultaneously in percent. The fuel quantity of 100 percent on the meter is equivalent to 350 pounds. Fuel pressure (psia) is shown on the FUEL PRESS meter on panel F8. Fuel quantity in percent is also displayed on the BFS SM SYS SUMM 2 display (FUEL QTY).

The gaseous nitrogen pressure in each fuel tank exerts a force on the tank’s diaphragm to expel the hydrazine fuel under pressure to the fuel distribution system. Filters are incorporated into each distribution line to remove any particles. The fuel distribution line branches into two parallel paths downstream of the filter. An isolation valve is installed in each parallel path, providing redundant paths to permit fuel flow to the APU or to isolate fuel from the fuel supply tanks.

APU Meters and Switches on Panel F8

Improved APU Fuel System Schematic

APU Fuel TK VLV Switches and Circuit Breakers on Panel R2

Fuel Tank Isolation Valves

Both isolation valves in each APU fuel distribution system are electrically powered solenoid valves, which are controlled by the corresponding APU FUEL TK VLV 1, 2, 3 switches on panel R2. They are energized open when the corresponding switch is positioned to OPEN; both valves are closed when the switch is positioned to CLOSE, or if electrical power is lost.

Each valve has a reverse relief function to relieve pressure on fuel trapped in the fuel distribution line downstream of the fuel tank valves when both valves are closed. The valve relieves the downstream pressure when the pressure increases 40 psi to 200 psi above fuel tank pressure due to heat soakback following APU shutdown.

The IAPU fuel tank isolation valves are cooled by fuel flow when the valves are open. Each valve has redundant temperature measurements (two per valve, four per APU). One temperature reading for each valve is displayed on the BFS SM SYS SUMM 2 display and the APU/HYD, DISP 86 display (Ops 201) beside the FU TK VLV AT and BT labels. There are two tank isolation valve circuit breakers per APU (one per valve) located on panel R2. These can be pulled to disconnect electrical power from the solenoid if a valve fails open or shorts. The valve heating profile, when the fuel is stagnant, is gradual and, in the event of a failed open valve or short, permits adequate time for corrective action.

Fuel Pump

Each APU fuel pump is a fixed-displacement, gear-type pump that discharges fuel at approximately 1,400 psi to 1,500 psi and operates at approximately 3,918 rpm. A fuel filter is located at the fuel pump outlet, and a relief valve relieves at approximately 1,725 psi back to the pump inlet if the filter becomes clogged.

Each fuel pump is driven by the turbine through the reduction gearbox. The fuel pump reduction gear is located in the lube oil system gearbox, and a shaft from the reduction gear drives the fuel pump. Seals are installed on the shaft to contain any leakage of fuel or lube oil. If leakage occurs through the seals, it is directed to a drain line that runs to a 500-cubic centimeter catch bottle for each APU. If the catch bottle were overfilled, it would relieve overboard at approximately 28 psia through a drain port. On ascent or entry, the flight crew can monitor the catch bottle’s line pressure on the BFS SM SYS SUMM 2 display (PMP LK P).

APU Information on BFS SM SYS SUMM 2 Display

Fuel Control Valves

The APU’s operating speed is controlled by the primary and secondary fuel control valves, which are installed in series downstream of the fuel pump. These are solenoid-operated pulsertype valves. In the normal APU operating mode, the primary control valve pulses to maintain the APU’s speed at about 74,000 rpm (103%), while the secondary control valve is powered fully open. If the APU is taken to high via the APU SPEED SELECT switch on panel R2, the primary valve is unpowered and goes to fully open, while the secondary valve begins pulsing, and controls APU speed at about 81,000 rpm (113%). If the secondary valve subsequently fails open, the primary valve will begin pulsing to maintain APU speed at about 83,000 rpm (115%) in the backup speed control mode. If the secondary valve loses power, it goes to the closed position and shuts down the APU. As noted above, the primary valve goes to full open if it loses power, allowing the secondary valve to take over automatically and control at high speed (113%).

The crew can see APU speed on the BFS SM SYS SUMM 2 display (APU SPEED %) in percent (100 percent = 72,000 rpm). The speed fluctuates due to the nature of the pulsemodulated fuel flow system.

For safety reasons, each APU has an automatic shutdown feature that will shut the APU down if the speed falls below 80 percent (57,600 rpm) or rises above 129 percent (92,880 rpm).

Gas Generator and Turbine

Each gas generator consists of a bed of Shell 405 catalyst in a pressure chamber, mounted inside the APU exhaust chamber. When the hydrazine fuel comes into contact with the catalyst, it undergoes an exothermic reaction, decomposing into a hot gas at approximately 1,700° F. The gas expands rapidly and makes two passes through a single-stage turbine wheel, passes over the outside gas generator chamber and exits overboard through its own independent exhaust duct, located near the base of the vertical stabilizer. The temperature of the hot gas at the exhaust duct is approximately 1,000° F.

The shaft power from the spinning turbine is sent to the hydraulic main pump associated with the APU via a speed reduction gearbox. It is also used to drive the APU’s fuel pump and lubrication oil pump.

The normal speed of the hydraulic main pump, APU fuel pump, and APU lube oil pump are 3,918 rpm, 3,918 rpm, and 12,215 rpm respectively. The lube oil system is necessary to lubricate the APU gearbox and the fuel pump.

The temperatures of the gas generator bed, the gas generator fuel injector, and the turbine exhaust gas are visible on the BFS SM SYS SUMM 2 CRT display (GG BED, INJ, TEMP EGT). While the APU is running, the gas generator bed temperature transducer goes offscale high at approximately 500° F. On orbit, when the APU is shut down, the gas generator bed temperature transducer is useful for monitoring the bed temperature when the bed is kept warm by heaters.

Lubricating Oil

The APU lube oil system is a scavenger-type system with a fixed-displacement pump. Each APU turbine through its gearbox drives a lube oil pump at 12,215 rpm. The system is pressurized with gaseous nitrogen to provide adequate suction pressure to start the lube oil pump under zero-gravity conditions. Each lube oil system has its own nitrogen gas storage vessel, which is pressurized to approximately 140 psia. The pressurization system for each lube oil system has a valve controlled by its corresponding APU controller. The gaseous nitrogen pressurization valve for each power unit is energized open by its corresponding controller when the gearbox pressure is below 5.2 psi, plus or minus 1.3 psi, to ensure that gearbox pressure is sufficiently above the requirements for proper scavenging and lube pump operation.

The pump increases the lube oil pressure to approximately 60 psi, directs the lube oil system through the corresponding water spray boiler for cooling, and returns the lube oil to the accumulators and gearbox. The two accumulators in each lube oil system allow thermal expansion of the lube oil, accommodate gas initially trapped in the external lube circuit, maintain lube oil pressure at a minimum of approximately 15 psia, and act as a zero-gravity, all-altitude lube reservoir.

The following information is transmitted to the BFS SM SYS SUMM 2 display by the APU controller via the GPC: lube oil pump outlet pressure (OIL OUT P) at approximately 45 psia, outlet temperature at approximately 270° F and return temperature from the water spray boiler (OIL IN, OUT) at approximately 250° F for each APU. The lube oil temperature of each APU is also monitored on the APU OIL TEMP meter on panel F8. The APU is selected by the switch below the meter.

APU OIL TEMP Meter and Switch on Panel F8

APU OIL TEMP Meter and Switch on Panel F8 (Note: EGT indicator on meter is driven by "TEMP EGT" transducer seen on BFS SYS SUMM 2 CRT Display.)

Electronic Controller

Each APU has its own digital controller. The controller detects malfunctions, controls turbine speed, gearbox pressurization, and fuel pump/gas generator heaters. Each controller is controlled by its corresponding APU CNTLR PWR switch on panel R2. When the switch is positioned to ON, 28-volt dc power is sent to that controller and APU. The controllers are redundantly powered via dual internal remote power controllers. When the switch is positioned to OFF, electrical power is removed from that controller and APU.

APU Start

An APU/HYD READY TO START talkback indicator for each APU is located on panel R2. The talkback signals gray when that APU hydraulic system is ready to start; that is, when the APU gas generator temperature is above 190° F, APU turbine speed is less than 80 percent, WSB controller is ready, corresponding APU fuel tank isolation valves are open, and corresponding hydraulic main pump is depressurized. When the APU is started, and its turbine speed is greater than 80 percent of normal speed, the corresponding indicator shows barberpole.

NOTE

A barberpole APU/HYD READY TO START talkback will not inhibit a start.

APU OPERATE 1, 2, 3 switches are located on panel R2. When the switches are positioned to START/RUN, the corresponding APU controller activates the start of that unit and removes electrical power automatically from the unit’s gas generator and fuel pump heaters.

To start the APU, fuel expelled from the hydrazine tank flows through the open tank valves and filter to the gas generator valve module, which contains a primary and secondary fuel control valve in series. The primary pulse control valve is normally open, and the secondary pulse control valve is energized open. Fuel flowing through the pump bypass valve is directed to the gas generator, because the fuel pump is not being driven at that moment by the APU turbine.

The fuel in the gas generator decomposes through catalytic reaction, creates hot gas, and directs the hot gas to the single-stage turbine, which begins to rotate. The turbine’s mechanical shaft drives the reduction gears, rotating the fuel pump, lube oil pump, and hydraulic pump. The fuel pump increases the fuel pressure at its outlet and sustains pressurized fuel to the gas generator valve odule and gas generator.

The startup logic delays the APU underspeed logic check for 10.5 seconds after the start command is issued. This allows the APU to reach normal operating speed before the shutdown logic begins checking for a speed lower than 80 percent. The auto shutdown capability of the controller can be disabled by taking the APU AUTO SHUT DOWN switch on panel R2 to INHIBIT.

The startup logic does not delay the APU overspeed logic. If an overspeed is detected at any time by the controller, the F7 and MASTER ALARM will annunciate. If the AUTO SHUT DOWN on panel R2 is ENABLED, the controller will automatically close the tank isolation valves and close the secondary control valve.

CAUTION

After an APU auto shutdown, the APU FUEL TK VLV switch must be taken to CLOSE prior to inhibiting auto shutdown logic. Failure to do so can allow the fuel tank isolation valves to reopen and flow fuel to an APU gas generator bed that is above the temperature limits for safe restart.

APU Speed Control

When the APU turbine speed exceeds the control target (103 percent for NORMAL and 113 percent for HIGH) the appropriate control valve closes. The fuel is then diverted through a bypass line back to the fuel pump inlet. When the turbine speed drops below the control target, the appropriate valve opens directing fuel to the gas generator and closing off the bypass line. The primary fuel valve pulses to maintain APU speed. The frequency and duration of the primary fuel control valve pulses are functions of the hydraulic load on the unit.

The secondary fuel control valve normally stays fully open during the operation of the primary. If the primary valve loses power, it goes to the fully open position, and the secondary valve begins pulsing and controlling APU speed. If the secondary valve loses power at any time, the APU is shut down. If the auxiliary power unit is taken to a high speed (by the APU SPEED SELECT switch on panel R2), the primary valve is unpowered and goes to the fully open position while the secondary valve controls the unit’s speed.

Each APU controller controls the speed of each unit upon the activation of the APU SPEED SELECT switch for each APU on panel R2. The NORM position controls the speed at 74,160 rpm, 103 percent, plus or minus 8 percent. The HIGH position controls the speed at 81,360 rpm, 113 percent, plus or minus 8 percent, with a second backup of 82,800 rpm, 115 percent, plus or minus 8 percent.

APU Auto Shutdown

The APU AUTO SHUT DOWN switches on panel R2 enable the automatic shutdown feature in the associated APU controllers. When the switch is positioned to ENABLE, each controller monitors its corresponding APU speed. If that APU speed falls below 57,600 rpm (80 percent) or rises above 92,880 rpm (129 percent), the controller automatically shuts down that unit. Each shutdown command closes that unit’s secondary fuel valve and the tank isolation valves.

APU Ready-for-Start Talkback Indicator Logic

When an APU AUTO SHUT DOWN switch is positioned to INHIBIT, the automatic shutdown sequence for its APU controller is inhibited. If the turbine speed falls below 80 percent or rises above 129 percent APU UNDERSPEED or APU OVERSPEED caution and warning lights on panel F7 will be illuminated, and a tone will be generated, even though the APU AUTO SHUT DOWN switch is in INHIBIT.

CAUTION

An APU should not be restarted after an overspeed shutdown. Uncontained overspeed and turbine wheel breakup could occur if restart is attempted.

APU/HYD Ready to Start Talkbacks, APU Operate Switches, APU Speed Select Switches, APU AUTO Shut Down Switches on Panel R2

APU Overspeed/Underspeed Detection

 

Injector Cooling System

The gas generator injector water cooling system is used only when the normal cool-down period of approximately 180 minutes is not available. The system sprays water to reduce the temperature of the gas generator injector branch passages to less than 400° F in the event that a hot APU must be restarted after it has been recently shut down. The water cooling ensures that the hydrazine will not detonate in the fuel line leading into the injector due to heat soakback from the gas generator. The injector is cooled by circulating water through it. The water from the gas generator injector is exhausted into the aft fuselage.

APU Injector Cooling

 

A single water tank located in the aft fuselage of the orbiter serves all three APUs. The water tank is 9.4 inches in diameter and loaded with 9 pounds (plus or minus 0.5 pound) of water. The water tank is pressurized with gaseous nitrogen at a nominal pressure of 120 psi. The pressure acts on a diaphragm to expel the water through three 0.25-inch-diameter lines to three control valves. When the APU OPERATE switch on panel R2 for APU 1, 2, or 3 is positioned to INJECTOR COOL, the water valve of that unit opens and directs the water into the gas generator injector to cool it.

If the injector branch (internal) temperature of an APU is above 400° F from heat soakback, or if the catalytic bed heater temperature is above 430° F, the flight crew must cool the injector for 3.5 minutes before starting the APU. Operational data from hot APUs shows that the GG INJ temperature does not accurately reflect the drop in injector branch temperatures. The crew is safe to attempt a restart if the GG INJ temperature is decreasing and at least 3.5 minutes of continuous injector cooling has been completed. A Class 3 alarm with message "APU 1 (2) Cooldown" will annunciate 225 seconds after APU injector cooling is initiated.

CAUTION

Care must be taken not to delay in the OFF position when taking the APU OPERATE switch to START/RUN. If cooldown is terminated more than 2 to 3 seconds prior to starting the APU, the injector branch temperatures may increase above start limits, and detonation may occur without another cooldown cycle.

The water tank supply is sufficient for about six hot starts, two per APU. The unit’s injector temperature can be monitored on the BFS SM SYS SUMM 2 display (INJ).

Fuel Pump and Gas Generator Valve Module Cooling

The fuel pump and gas generator valve module are cooled by passive cooling. The improved APUs have passive heat sinks and heat shields to absorb conductive and radiant heat. This prevents excessive heat soakback in the gas generator valve and fuel pump assemblies. There are no water tanks or associated plumbing for this module with the APUs. The crew has no requirement to do anything to provide cooling. This passive cooling system, in conjunction with active injector cooling, is used to allow for contingency restarts in the event a deorbit becomes necessary within approximately 180 minutes of APU shutdown.

CAUTION

An APU may not be restarted if the temperature of the fuel pump is above 210° F or the temperature of the gas generator valve module is above 200° F, because hydrazine detonation may occur.

APU Heaters

The APU HEATER TANK/FUEL LINE/H2O SYS 1A, lB, 2A, 2B, 3A, 3B switches on panel A12 operate the thermostatically controlled heaters located on the corresponding APU fuel system and water system. The fuel tank, fuel line, and water line heaters for each APU are divided into redundant A and B systems for each unit. For example, for APU 1, 1A and 1B, the TANK/FUEL LINE/H2O SYS 1A switch controls the A heaters, and the thermostats provide automatic control. Only one set of heaters is used at a time. The 1B switch controls the 1B heaters, and the thermostats provide automatic control. The APU fuel tank and line heater thermostats maintain the temperatures between a nominal 55° F and 65° F. The water system heater thermostats maintain the temperatures between 55° F and 65° F. The OFF position of each switch removes power from the respective heater circuits.

The APU HEATER GAS GEN/FUEL PUMP 1, 2, 3 switches on panel A12 operate thermostatically controlled heaters located on the corresponding APU, fuel pump, and gas generator valve module, and provide power to the gas generator bed heater. The thermostats control a series of heaters on the gas generator valve module, fuel pump, and all the fuel lines and the water lines from the fuel pump spray manifold to the gas generator valve module. The heaters are divided into redundant A and B systems for each APU. The A AUTO switch controls the A heater, and the A thermostat automatically controls the corresponding APU fuel pump heater, maintaining fuel pump and gas generator valve module temperatures at about 100° F. The gas generator bed heater is maintained between 360° and 425° F by a compactor in the APU controller, which receives its signal from the bed temperature transducer. The gas generator temperature range ensures efficient APU startup through efficient catalytic reaction. The B AUTO switch position provides the same capability for the B heater system. The gas generator and fuel pump heaters are automatically deactivated by the corresponding controller at APU start. The OFF position of each switch removes power from the respective heater circuits. These heater switches also provide redundant power to the gas generator and gearbox pressure signal conditioners for use while the APU controller is off.

The lube oil system lines on each APU also have a heater system. These heaters are controlled by the APU HEATER LUBE OIL LINE 1, 2, 3 switches on panel A12. The lube oil line heaters for each APU are also divided into an A and B system: e.g., for 1, A AUTO and B AUTO. The A AUTO switch controls the A heater, and the thermostat automatically controls the corresponding lube oil system heater, maintaining the lube oil line in the temperature range of 55° F to 65° F. The B AUTO switch position provides the same capability to the B heater system. The OFF position of each switch removes power from the respective heater circuits.

APU Heater Controls on Panel A12

 

Water Spray Boilers

The water spray boiler (WSB) system consists of three identical independent water spray boilers, one for each APU and hydraulic system. The boilers are located in the aft fuselage of the orbiter. Each WSB cools the corresponding APU lube oil system and hydraulic system by spraying water onto their lines; as the water boils off, the lube oil and hydraulic fluid are cooled. The steam that boils off in each water spray boiler exits through its own exhaust duct, located on the starboard side of the vertical stabilizer.

Each WSB is 45 by 31 inches long by 19 inches wide, and including controller and vent nozzle, weighs 181 pounds. They are mounted in the orbiter aft fuselage between Xo 1340 and 1400, at Zo 488 minus 15, and at Yo plus 15. Insulation blankets cover each boiler. The boiler's water capacity is 142 pounds.

Each WSB stores water in a bellows-type storage tank pressurized by gaseous nitrogen providing positive water expulsion to feed the boiler. Hydraulic fluid passes through the boiler three times. APU lube oil passes through the boiler twice. The hydraulic fluid tubes are sprayed with water from three water spray bars, and two water spray bars spray the APU lube oil. Separate water feed valves allow independent control of the hydraulic fluid spray bars and APU lube oil spray bars. Redundant electrical controllers provide completely automatic operation.

The boiler system maintains APU lube oil temperature at approximately 250° F and the hydraulic fluid in the range of 210° to 220° F. The crew can see the WSB water quantity (H2O QTY), nitrogen tank pressure (N2 P), nitrogen regulator pressure (REG P), and nitrogen tank temperature (N2 T) on the right side of the SM APU/HYD (DISP 86) display on orbit.

Water Spray Boiler Unit

SM APU/HYD Display (DISP 86)

Water Spray Boiler

 

Nitrogen Supply System

The gaseous nitrogen pressure for each WSB is contained in a corresponding 6-inch spherical pressure vessel. The pressure vessel contains 0.77 pound of nitrogen at a nominal pressure of 2,400 psi at 70° F. The gaseous nitrogen storage system of each WSB is directed to its corresponding water storage tank. Each storage vessel contains sufficient nitrogen gas to expel all the water from the tank and allow for relief valve venting during ascent.

The nitrogen shutoff valve between the pressure valve and water storage tank of each boiler permits the pressure to reach the nitrogen regulator and water tank or isolates the nitrogen supply from the water tank. Each nitrogen valve is controlled by its respective BOILER N2 SUPPLY 1, 2, or 3 switch on panel R2. The nitrogen shutoff valve, which is latched open or closed, consists of two independent solenoid coils that permit valve control from either the primary or secondary controller.

A single-stage regulator is installed between the nitrogen pressure shutoff valve and the water storage tank. The gaseous nitrogen regulator for each water spray boiler regulates the highpressure nitrogen between 24.5 and 26 psig as it flows to the water storage tank. A relief valve is incorporated inside each nitrogen regulator to prevent the water storage tank pressure from exceeding 33 psig. The gaseous nitrogen relief valve opens between 30 to 33 psig.

Water Supply System

The water supply for each boiler is stored in a positive-displacement aluminum tank containing a welded metal bellows separating the stored water inside the bellows from the nitrogen expulsion gas.

Boiler Switches on Panel R2

Redundant pressure and temperature sensors located downstream from the gaseous nitrogen pressure vessel and on the water tank for each boiler transmit the pressures and temperatures through each controller to the systems management general-purpose computer. The computer computes the water tank quantity from the pressure, volume, and temperature, and transmits the water tank quantity to panel F8 for each boiler. The switch below the meter on panel F8 is positioned to H2O to allow the water quantity of each boiler to be displayed on the APU FUEL/H2O QTY 1, 2, or 3 meter. Water quantity is available when either the A or B controller is powered.

Downstream of the water storage tank, the feedwater lines to each water boiler split into two parallel lines: one line goes to the hydraulic fluid flow section and one to the lube oil section of the WSB. The H2O spray valves in each feedline are controlled independently by the boiler controller.

Temperature Control

The two boiler controllers are operated by the respective BOILER CNTLR/HTR 1, 2, and 3 switches on panel R2. When the applicable switch is positioned to A, the A controller for that boiler is powered; if it is positioned to B, the B controller is powered. The OFF position removes electrical power from both controllers.

APU FUEL/H2O QTY Meter and Switch on Panel F8

 

The BOILER PWR 1, 2, and 3 switches on panel R2 enable (provide the automatic control functions) the specific controller A or B selected for that boiler by the BOILER CNTLR/HTR 1, 2, and 3 switches on panel R2. When the applicable controller A or B is enabled for that boiler, a ready signal is transmitted to the corresponding APU/HYD READY TO START indicator on panel R2 if the following additional conditions are met: gaseous nitrogen shutoff valve is open, steam vent nozzle temperature is greater than 130° F, and hydraulic fluid bypass valve is in the correct position with regard to the hydraulic fluid temperature.

The core of each WSB is a stainless steel crimped-tube bundle. The hydraulic fluid section is divided into three 17-inch-long passes of smooth tubes (first pass-234 tubes, second pass-224 tubes, and third pass-214 tubes). The lube oil section of the APU comprises two passes with 103 crimped tubes in its first pass and 81smooth tubes in the second pass. The tubes are 0.0125 of an inch in diameter with a wall thickness of 0.010 of an inch. Crimps located every 0.24 of an inch break up the internal boundary layer and promote enhanced turbulent heat transfer. Although the second pass is primarily a low-pressure drop return section, approximately 15 percent of the unit's lube oil heat transfer occurs there. Three connected spray bars feed the hydraulic fluid section, while two spray bars feed the power unit's lube oil section in each boiler.

When the orbiter is in the vertical position on the launch pad, each boiler is loaded with up to 3.5 pounds of water, which is referred to as "pool mode" operation. When each APU/hydraulic system and WSB are in operation 5 minutes before lift-off, the APU lube oil tube bundle is immersed in the boiler water precharge. Liquid level sensors in each water boiler prevent the water feed valves from pulsing to avoid water spillage or loss. As the vehicle ascends during launch, the lube oil system of the APU heats up, eventually the boiler water precharge boils off, and the boiler goes into the spray mode about 8 minutes after launch. The hydraulic fluid usually does not heat up enough during ascent to require spray cooling.

When the APU/hydraulic combination is started for atmospheric entry, the hydraulic fluid and power unit lube oil flow commences, fluid temperatures rise, and spraying is initiated as required. During the lower part of entry, when the boiler temperature reaches 188° F, the water spray boiler returns to the pool mode. The spray bars begin discharging excess water to fill the boiler. When the water reaches the liquid level sensors, the spray is turned off so that the boiler is not overfilled. During entry, because the orbiter's orientation is different from that of launch, the boiler can hold up to 14 pounds of water.

The enabled controller of the operating WSB monitors the hydraulic fluid and lube oil outlet temperature from the APU. The hydraulic fluid outlet temperature controls the hydraulic fluid H2O spray control valve, and the lube oil outlet temperature controls the lube oil water spray control valve. Signals are based on a comparison of the hydraulic system fluid temperature to its 208° F set point and of the lube oil of the power unit to its 250° F set point. When the respective water feed valve opens, instantaneous flows of 10 pounds per minute maximum through the hydraulic section and 5 pounds per minute maximum through the lube oil section enter the water boiler through the corresponding spray bars to begin evaporative cooling of the hydraulic fluid and APU lube oil. The steam is vented out through the overboard steam vent. The separate water feed valves modulate the water flow to each section of the tube bundle core in each WSB independently in 200-millisecond pulses that vary from one pulse every 10 seconds to one pulse every 0.25 of a second. Because of the unique hydraulic system fluid flows, control valves are located in the hydraulic system fluid line section of each WSB.

Normally, hydraulic system fluid flows at up to 21 gallons per minute; however, the hydraulic system experiences 1- to 2-second flow spikes at up to 63 gallons per minute. If these spikes were to pass through the boiler, pressure drop would increase ninefold and the boiler would limit the flow of the hydraulic system. To prevent this, a relief function is provided by a spring- loaded poppet valve that opens when the hydraulic fluid pressure drop exceeds 48 psi and is capable of flowing 43 gallons per minute at a differential pressure of 50 psi across the boiler. A temperature controller bypass valve allows the hydraulic fluid to bypass the boiler when the fluid temperature decreases to 190° F. At 210° F, the controller commands the bypass valve to direct the fluid through the boiler. When the hydraulic fluid cools to 190° F, the controller again commands the valve to route the fluid around the boiler. Bypass valve (BYP VLV) status is available on the following displays: SM SYS SUMM 2 (PASS AND BFS) and PASS DISP 86 APU/HYD.

Heaters

Each water boiler, water tank, and steam vent is equipped with electrical heaters to prevent freeze-up in orbit. The water tank and boiler electrical heaters are activated by the corresponding BOILER CNTLR/HTR 1, 2, and 3 switches on panel R2. The A or B position of each switch selects the A or B heater system and is automatically controlled by the corresponding A or B controller. The steam vent heaters are also activated by the BOILER CNTLR/HTR 1, 2 and 3 switches but only if the BOILER PWR 1, 2 or 3 switch on panel R2 is ON. The water tank and boiler heaters are cycled on at 50° F and off at 55° F. The steam vent heaters are not operated continuously in orbit; they are activated approximately two hours before APU startup. The steam vent heaters are cycled on at 150° F and cycled off at 175° F.

Main Hydraulic Pump

The main hydraulic pump for each hydraulic system is a variable displacement type. Each operates at approximately 3,900 rpm when driven by the corresponding APU. Each main hydraulic pump has an electrically operated depressurization valve. The depressurization valve for each pump is controlled by its corresponding HYD MAIN PUMP PRESS 1,2, or 3 switch on panel R2. When the switch is positioned to LOW, the depressurization valve is energized to reduce the main hydraulic pump discharge pressure from its nominal range of 2,900 to 3,100 psi output to a nominal range of 500 to 1,000 psi to reduce the APU torque requirements during the start of the APU. "APU Press Low" is one of the inputs required to get a gray READY TO START talkback.

NOTE

An APU cannot be successfully started with HYD MAIN PUMP PRESS positioned to NORM.

After an APU has been started, the corresponding HYD MAIN PUMP PRESS switch is positioned from LOW to NORM. This de-energizes the respective depressurization valve, allowing that hydraulic pump to increase its outlet pressure from 500 to 1,000 psi to 2,900 to 3,100 psi. Each hydraulic pump is a variable displacement type that provides 0 to 63 gallons per minute at 3,000 psi nominal with the APU at normal speed and 69.6 gallons per minute at 3,000 psi nominal with the APU at high speed.

Main pump outlet pressure (HYD PRESS) can be seen by the crew on the BFS SM SYS SUMM 2 or PASS DISP 86 APU/HYD displays. A high pressure relief valve in the filter module for each hydraulic system also relieves the hydraulic pump supply line pressure into the return line in the event the supply line pressure exceeds 3,850 psid.

A separate pressure sensor (sensor A) in the filter module for each hydraulic system monitors the hydraulic system source pressure and displays the pressure on the HYDRAULIC PRESSURE 1, 2, and 3 meters on panel F8. This hydraulic pressure sensor also provides an input to the yellow HYD PRESS caution and warning light on panel F7 if the hydraulic pressure of system 1, 2, or 3 is below 2,400 psi.

HYD MAIN PUMP PRESS 1,2,3 Switches on Panel R2

Hydraulic System Schematic

HYDRAULIC PRESSURE and QUANTITY Meters on Panel F8

Hydraulic Reservoir

Hydraulic reservoir pressure is maintained using an accumulator bootstrap mechanism. The bootstrap uses a variable area piston assembly to convert high pressure to the accumulator to lower pressure in the reservoir (roughly 40:1). This reservoir pressure maintains adequate hydraulic inlet pressure at both the main pump and circulation pump to prevent cavitation during startup and operation. When the main hydraulic pump is in operation, the high-pressure side of the piston and the bootstrap accumulator are pressurized to 3,000 psig from the main pump discharge line. When the main hydraulic pump is shut down, the priority valve closes, and the bootstrap accumulator maintains a pressure of approximately 2,500 psi. The 2,500 psi on the high side results in a main pump inlet (low side) pressure of approximately 62 psia. The minimum inlet pressure to assure a reliable main pump start is 20 psia (which corresponds to a high-pressure side of 800 psi). This prevents the main pump from cavitating (not drawing hydraulic fluid), which could damage the pump.

The quantity in each reservoir is 8 gallons. The hydraulic fluid specification is MIL-H-83282, which is a synthetic hydrocarbon (to reduce fire hazards). The reservoir provides for volumetric expansion and contraction. The quantity of each reservoir is monitored in percent on the HYDRAULIC QUANTITY meters on panel F8. A pressure relief valve in each reservoir protects the reservoir from overpressurization and relieves at 120 psid.

Hydraulic Accumulator

The accumulator is a piston type precharged with gaseous nitrogen at 1,650 to 1,750 psi. The gaseous nitrogen capacity of each accumulator is 96 cubic inches, and the hydraulic volume is 51 cubic inches.

Circulation Pump and Heat Exchanger

The circulation pump is actually two fixed displacement gear-type pumps in tandem, driven by a single motor. One is a high pressure, low-volume pump (2,500 psig), which is used to maintain accumulator pressure while the hydraulic system is inactive in orbit. The other is a low pressure, high-volume pump (350 psig), which is used to circulate hydraulic fluid through the orbiter hydraulic lines while the hydraulic system is inactive in orbit in order to warm up cold spots. The hydraulic fluid is circulated through a Freon/hydraulic fluid heat exchanger to pick up heat from the orbiter Freon coolant loops. A temperature-controlled bypass valve directs the hydraulic fluid through the heat exchanger if the temperature at the heat exchanger inlet is less than 105° F. The bypass valve bypasses the fluid around the heat exchanger if the temperature is greater than 115° F.

An unloader valve at the circulation pump outlet directs the high pressure output from the circulation pump into the accumulator until the accumulator pressure is greater than 2,563 psia, then redirects the high pressure output to combine with the low pressure output to the hydraulic lines.

BFS SM SUMM 2 Display

HYD CIRC PUMP Switches on Panel R2

 

Each circulation pump can be manually turned on or off with the corresponding HYD CIRC PUMP switch on panel R2. If the switch is placed in GPC, the pump will be activated and deactivated by the SM GPC according to a control software program based on certain hydraulic line temperatures and/or accumulator pressure. This program activates the appropriate circulation pump when any of the control temperatures drop below either 0° F, or - 10° F, depending on their locations, and deactivates the circulation pump when all of the control temperatures for that system are greater than 20° F, or after 15 minutes for system 1 and 10 minutes for systems 2 and 3. The activation/deactivation limits for these control temperatures can be changed during the flight by crew or Mission Control.

The program also includes a timer to limit the maximum time a circulation pump will run, and a priority system to assure that only one circulation pump is on at a time (because of excessive power usage if more than one circulation pump is on). Each circulation pump uses 2 kW of electrical power. This software will also automatically provide for the repressurization of the hydraulic accumulator when the pressure lowers to a value of 1,960 psi. In this contingency, the circulation pump will first receive the highest priority to operate and will be turned ON while other circulation pumps are operating in thermal mode (this means that two pumps can be operating simultaneously). After the pump has been repressurized, the accumulator above 1,960 psi, or a period of 2 minutes (this value can be changed by Mission Control Center uplink) has elapsed, the circulation pump will be commanded to OFF. It is possible to run all three circulation pumps at the same time to repressurize accumulators. The circulation pump is automatically disconnected when its corresponding APU Run command is issued by the APU controller. Each circulation pump can be powered by one of two orbiter main electrical buses, selectable by the

HYD CIRC PUMP POWER switches on panel A12.

The crew can see circulation pump outlet pressure as well as the hydraulic line and component temperatures on the PASS SM HYD THERMAL display, DISP 87.

Hydraulic System Controls on Panel A12

SM HYD THERMAL Display (DISP 87)

The SM APU/HYD display (DISP 86) shows the hydraulic system pressure, reservoir temperature, reservoir quantity (in percent), and hydraulic accumulator pressure.

Hydraulic Heaters

Areas of the hydraulic lines that cannot be warmed by fluid circulation while the system is inactive on-orbit are warmed by heaters. These heaters are automatically controlled by thermostats to maintain the hydraulic line temperatures in a specified range. Each heated area has redundant heaters (A and B), which are controlled by the HYDRAULIC HEATER switches on panel A12.

Operations

The WSB controllers are powered up at launch minus 8 hours, and the boiler water tanks are pressurized in preparation for APU activation. The controllers activate heaters on the water tank, boiler, and steam vent to assure that the water spray boiler is ready to operate for launch.

APU start is delayed as long as possible to save fuel. At T minus 6 minutes 15 seconds, the pilot begins the prestart sequence. The pilot confirms that the WSB is activated, then activates the APU controllers and depressurizes the main hydraulic pump. Depressurizing the main pump reduces the starting torque on the APU. The pilot then opens the fuel tank valves and looks for three APU ready-to-start indications (gray talkbacks). At T minus 5 minutes, the pilot starts the three units by setting the APU OPERATE switches to START/RUN and checks the hydraulic pressure gauges for an indication of approximately 800 psi. Then the pilot pressurizes the main pump and looks for approximately 3,000 psi on the gauges. All three hydraulic main pump pressures must be greater than 2,800 psi by T minus 4 minutes, or the automatic launch sequencer will abort the launch.

The APUs operate during the ascent phase and continue to operate through the first OMS burn. At the conclusion of the main engine purge, dump, and stow sequence, the APUs and WSBs are shut down. The same sequence applies for a delayed OMS-1 burn. If an abort once around is declared, the APUs are left running, but the hydraulic pumps are depressurized to reduce fuel consumption. The units are left running to avoid having to restart hot APUs for deorbit and re-entry.

Six hours after lift-off, or as soon as they are required, depending on the environment, the gas generator/fuel pump heaters are activated and are in operation for the remainder of the orbital mission. The fuel and water line heaters are activated immediately after APU/HYD SHUTDN in the post OMS-1 timeframe to prevent the lines from freezing as the APUs cool down.

Two hours after lift-off, the steam vent heaters of the WSBs are turned on and left on for about 1.5 hours to eliminate all ice from the steam vents.

Two hours and twenty minutes into the flight, while in the Post Insertion Checklist, the hydraulic thermal conditioning is enabled by taking the hydraulic circulation pumps to GPC. Further, the HYD CIRC PUMP POWER switch(es) on panel A12 will be configured to distribute electrical loads when appropriate.

While the vehicle is in orbit, the hydraulic circulation pumps are in the GPC mode--automatically activated when hydraulic line temperatures become too low and automatically deactivated when the lines warm up sufficiently.

On the day before deorbit, one APU is started to supply hydraulic pressure for flight control system checkout. (Hydraulic pressure is needed to move the orbiter aerosurfaces as part of this checkout.) The associated WSB controller is activated, landing gear isolation valves 2 and 3 are closed, and one APU (selected by the Mission Control Center) is started. The hydraulic main pump is set to normal pressure (approximately 3,000 psi), and aerosurface drive checks are made. After about 5 minutes, the checks are complete, and the APU is shut down. Normally, the unit does not run long enough to require WSB operation. The landing gear isolation valves on hydraulic systems 2 and 3 are reopened after the APU is shut down.

At 2.5 hours before the deorbit burn, the boilers' steam vent heaters are activated to prepare the system for operation during atmospheric entry. At about the same time, the landing gear isolation valves on hydraulic systems 2 and 3 are closed, and the circulation pumps are turned off.

At 45 minutes before deorbit, the WSB water tanks are pressurized, the APU controllers are activated, and the main hydraulic pumps are set to low pressure. The pilot opens the fuel tank valves and looks for three gray APU/HYD READY TO START talkbacks. The pilot then closes the fuel tank valves. This procedure takes place while the crew is in contact with the ground so that flight controllers can observe APU status. Five minutes before the deorbit burn, one APU (selected by Mission Control) is started to ensure that at least one unit will be operating for entry. The hydraulic pump is left in low-pressure operation. The APU operates through the deorbit burn. At 13 minutes before entry interface (400,000-foot altitude), while the orbiter is still in free fall, the other two APUs are started, and all three hydraulic pumps arepressurized to normal. Two main engine hydraulic isolation valves are cycled open and then closed to ensure that the engines are stowed for entry. Two minutes later, if required, the aerosurfaces are put through an automatic cycle sequence to make sure warm hydraulic fluid is available in the aerosurface drive units.

After touchdown, a hydraulic load test may be done to test the response of the auxiliary power units and hydraulic pumps under high load (i.e., high flow demand) conditions. This test cycles the orbiter aerosurfaces with one hydraulic system at a time in depressed mode (the remaining two APUs and hydraulic pumps have to drive all the aerosurfaces). This is typically done on the first flight of a new vehicle. Then the main engine hydraulic isolation valves are opened again, and the engines are set to the transport position. At this point, the hydraulic systems are no longer needed; the APUs and WSBs are shut down.

APU/HYD Caution and Warning Summary

The yellow APU TEMP caution and warning light on panel F7 is illuminated if the APU 1, 2, or 3 lube oil temperature is above 290° F.

The yellow APU OVERSPEED light is illuminated if APU 1, 2, or 3 turbine speed is more than 92,880 rpm (129%). If the APU AUTO SHUT DOWN switch on panel R2 is in ENABLE, an automatic shutdown of that APU will occur.

The yellow APU UNDERSPEED light is illuminated if APU 1, 2, or 3 turbine speed is less than 57,600 rpm (80%). If the APU AUTO SHUT DOWN switch for that APU is in ENABLE, an automatic shutdown will occur.

Placing the APU AUTO SHUT DOWN switch in INHIBIT only inhibits the automatic shutdown of that APU if its turbine speed is less than 80% or more than 129%. The APU UNDERSPEED or APU OVERSPEED light will always illuminate, and a tone will be generated.

The yellow HYD PRESS light illuminates when hydraulic system 1, 2, or 3 drops below 2,400 psi for any reason.

The blue SM ALERT illuminates, and the C/W tone is sounded if turbine speed falls below 80% or rises above 129%.

 The red BACKUP C/W ALARM illuminates if hydraulic pressure of system 1, 2, or 3 drops below 2,400 psi.

 

APU/HYD Caution and Warning Lights on Panel F7

 

APU/HYD Summary Data

The APU is a hydrazine-fueled, turbine driven power unit that generates mechanical shaft power to drive a hydraulic pump that produces pressure for the orbiter's hydraulic system.

The three orbiter hydraulic systems provide pressure to position hydraulic actuators for: gimbaling SSMEs, actuating SSME control valves, moving orbiter aerosurfaces, retracting ET disconnect umbilicals, deploying landing gear, and providing brake power, anti-skid, and nose wheel steering.

The APUs are located in the aft fuselage of the orbiter.

Each APU/HYD system has an independent water spray boiler for APU lube oil and hydraulic fluid cooling. Water is used after APU shutdown for injector cooling if a hot restart is required. The APUs share a central supply tank for injector cooling.

The three APUs are started 5 minutes before lift-off. They continue to operate throughout the launch phase, and are shut down after the main engine propellant dump and stow are completed (post OMS-1). The APUs are restarted for entry: one APU prior to the deorbit burn, and the other two prior to entry interface.

Each APU fuel tank load is approximately 325 pounds of hydrazine.

APU/HYD controls are located on Panel R2; heater controls are on panel A12.

CRTs that display APU/HYD information include the PASS and BFS SM SYS SUMM 2 display (DISP 79), APU/HYD display (DISP 86), HYD THERMAL (DISP 87), and APU/ENVIRON THERM (DISP 88).

Several meters for monitoring APU/HYD parameters are located on panel F8.

APUs can be manually shut down and restarted after completion of a full injector water cooling cycle (3.5 minutes), or after approximately 180 minutes of passive cooling on orbit.

APU/HYD Rules of Thumb

APU fuel usage rates vary with loading, but average 1% per minute (3 to 3.5 lbs/minute). Usage rates are reduced by about half if the hydraulic main pump is taken to low pressure (HYD MAIN PUMP PRESS switch on panel R2 set to LOW), as is done during the abort once around deorbit coast period.

The APU injector cooling tank shared by all three APUs contains enough water for 21 minutes of continuous flow. This is enough for six complete 3.5-minute hot restart injector cooling cycles.

If all water spray boiler cooling is lost to the lube oil after an APU reaches full operating temperatures, only 2 to 3 minutes of operating time are available before bearing seizure occurs.

APU/Hydraulic Overview

 

Panel R2

Panel F8

Panel 12

DISP 79 SM SYS SUMM 2 Display (PASS and BFS)

SM HYD Thermal Display (PASS DISP 87)

SM APU/HYD Display (PASS DISP 86)

APU/Environ Therm (PASS DISP 88)