EFTA00609974.pdf

Title Page Prey Page Next Page TOC Submit PCR GULFSTREAM IV MAINTENANCE MANUAL AIR CONDITIONING AND PRESSURIZATION SYSTEM - SYSTEM DESCRIPTION 1. General A. Description The environmental control system provides for pressurization, heating, cooling, ventilation and the means for reduction of humidity in flight or on the ground. True air conditioning is classified as heating or cooling as necessary to maintain a specific level of temperature within the occupied areas of the aircraft, regardless of the ambient temperatures or the operating conditions. Pressurization is the control over the pressure within the occupied areas. Supplemental cooling air to the left radio rack, right radio rack, nose compartment, cockpit pedestal, Cathode Ray Tube (CRT) display No. 1 and CRT display No. 2 is provided by mounted fans. The cooling fans help to prevent avionics and electronics equipment from overheating and malfunctioning by circulating air over and around equipment. The air conditioning system is a 3-wheel, air bearing, Air Cycle Machine (ACM), packaged refrigeration unit, which controls the cabin and cockpit temperature by means of mixing hot compressed air and refrigerated compressed air. The dual pack concept provides redundancy in case one unit fails. By air cycle, it is meant that cooling is provided by means of a thermodynamic cycle using only air as the medium (as opposed to vapor cycle systems which employ Freon or other similar gases). The system also employs water separation for humidity reduction. The pressurization system consists of electronic sensing and regulating devices which control the amount of air leaving the aircraft. A pneumatic safety valve is also incorporated, which will automatically regulate the maximum pressure in the aircraft should the automatic electronic control system fail to function properly. If required, the safety valve will limit the maximum pressure buildup within the pressurized areas (safety pressure relief) and also is the primary control device over the maximum negative pressure (vacuum differential). Suitable controls and indications for the system are located in the cockpit to enable the crew to perform programming, select automatic or manual modes of control, observe the status of the system with appropriate indicators and be alerted to possible malfunctions by means of appropriate warning devices. During normal in-flight operation, hot compressed air is supplied from the bleed air manifold. This is High Pressure (HP) bleed air which is temperature and pressure controlled and can be obtained from either or both engines by the selection of the crew. Cooling is provided by air cycle cooling equipment consisting of a primary heat exchanger, a secondary heat exchanger and a air cycle machine which are capable of reducing the temperature of the air from the bleed air manifold to values below ambient. Humidity reduction is accomplished by a mechanical water separator. Temperature control of the occupied areas is accomplished by varying the amounts of hot bleed air manifold air which bypasses the cooling equipment. Separate temperature control is provided for the cabin and the cockpit through controls located in the cockpit overhead panel. A feature of the air conditioning system is that it functions independently when on the ground. Although the main engines are not operating, and without a ground pneumatic supply (ground cart) or external electrical supply, complete air conditioning is provided by the auxiliary power unit supplying the hot compressed air for the bleed air manifold. The ground operation of the air conditioning system is essentially the same as in flight except that air flow across the heat exchangers is achieved by the use of a pneumatically driven cooling fan which is rigidly attached to the ACM turbine wheels by a common drive shaft. Provisions are also supplied for an external air connection, whereby an external ground hot compressed air source may be used to supply the bleed air manifold and in turn the air conditioning system. Should either or both engines be operating, the crew may select either or both engines as a supply of hot compressed air for the bleed air manifold and in turn the air conditioning system, in the same manner as for the in-flight operation. 21-00-00 Page 1 April 30/13 EFTA00609974 Title Page Prey Page Next Page TOC Submit PCR GUI.FSTREAM IV MAINTENANCE MANUAL Ram air ventilation is provided from the dorsal fin ram air duct during certain emergency procedures. Normal control over occupied area pressure is exercised by the crew through a completely electronic pressurization system, which features two modes of control over the outflow valve from two different electrical sources, backed up by a purely pneumatic safety valve in the event of total electrical malfunction. Normal flight operation is programmed by the crew through controls located in the overhead panel and copilot lower outboard instrument panel. A minimum of actions are required in flight since the majority of the programming can be accomplished by the crew while on the ground before takeoff. The system features barometric correction capabilities and programming of all flight and landing settings. These settings may be changed by the crew enroute it necessary. It utilizes the latest analog devices incorporated with reliability, safety and passenger comfort as the prime considerations. Numerous safety and backup devices are provided in the overall system, including: • Manual electrical control over the system should the automatic system malfunction or if selected by crew • Depressurization rate detection and limiting • Pressurization rate limiting (pneumatic) • Independent safety pressure relief and maximum vacuum differential relief (pneumatic) 2. Major Component Locations NO. PER UNIT LOCATION AtC Nose compartment cooling fan 1 Nose avionics bay, Fuselage Station (FS) 63 Nose compartment commutating module 1 Nose avionics bay, FS 63 Cabin DFRN PRESS indicator (digital) 1 Cockpit overhead panel CABIN ALT indicator (digital) 1 Cockpit overhead panel Cabin RC indicator (digital) 1 Cockpit overhead panel CABIN PRESSURE CONTROL 1 Cockpit overhead panel BLEED AIR indicator 1 Cockpit overhead panel CABIN / CKPT TEMP CONTROL indicator 1 Cockpit overhead panel (digital) Cabin temperature selector rheostat (MAN) 1 Cockpit overhead panel Cockpit temperature selector rheostat 1 Cockpit overhead panel (MAN) L BLEED AIR circuit breaker 1 Pilot Overhead circuit breaker panel R BLEED AIR circuit breaker 1 Pilot Overhead circuit breaker panel CKPT/CABIN TEMP IND circuit breaker 1 Pilot Overhead circuit breaker panel CABIN PRESS 28V circuit breaker 1 Pilot Overhead circuit breaker panel AIR INLET DOOR circuit breaker 1 Pilot Overhead circuit breaker panel CABIN PRESS 115V circuit breaker 1 Pilot Overhead circuit breaker panel 21-00-00 Page 2 April 30/13 EFTA00609975 Title Page Prey Page Next Page TOC Submit PCR GULFSTREAM IV MAINTENANCE MANUAL NO. PER UNIT LOCATION A/C CABIN PRESS IND circuit breaker 1 Pilot Overhead circuit breaker panel L BLEED AIR IND circuit breaker 1 Pilot Overhead circuit breaker panel R BLEED AIR IND circuit breaker 1 Pilot Overhead circuit breaker panel BLEED AIR ISO S/O V circuit breaker 1 Pilot Overhead circuit breaker panel CKPT TEMP CONT circuit breaker 1 Pilot Overhead circuit breaker panel L AIR COND circuit breaker 1 Pilot Overhead circuit breaker panel R AIR COND circuit breaker 1 Pilot Overhead circuit breaker panel SGL PACK circuit breaker 1 Pilot Overhead circuit breaker panel CABIN TEMP CONT circuit breaker 1 Pilot Overhead circuit breaker panel ADC XFER circuit breaker 1 Pilot Overhead circuit breaker panel NUTCRACKER circuit breaker 1 Copilot Overhead circuit breaker panel WARN LTS PWR #1 circuit breaker 1 Pilot circuit breaker panel WARN LTS PWR #2 circuit breaker 1 Pilot circuit breaker panel WARN LTS PWR #8 circuit breaker 1 Pilot circuit breaker panel WARN LTS PWR #10 circuit breaker 1 Pilot circuit breaker panel PED COOL FAN circuit breaker 1 Copilot circuit breaker panel LH RR COOL FAN circuit breaker 1 Copilot circuit breaker panel NOSE COMPT COOL VLV circuit breaker 1 Copilot circuit breaker panel DISPLAY MASTER #1 circuit breaker 1 Copilot circuit breaker panel DISPLAY MASTER #2 circuit breaker 1 Copilot circuit breaker panel DADC #1 circuit breaker 1 Copilot circuit breaker panel DADC #2 circuit breaker 1 Copilot circuit breaker panel DISPLAYS FAN #1 circuit breaker 1 Copilot circuit breaker panel DISPLAYS FAN #2 circuit breaker 1 Copilot circuit breaker panel RH RR COOL FAN circuit breaker 1 Copilot circuit breaker panel RH RR FAN CONT circuit breaker 1 Copilot circuit breaker panel Cabin pressurization selector 1 Copilot outboard skirt panel Radio rack fan conrol panel 1 Copilot side console Cabin / cockpit temperature control sensor 1 Left side of pedestal Cockpit pedestal cooling fan 1 Lower rear of pedestal 21-00-00 Page 3 April 30/13 EFTA00609976 Title Page Prey Page Next Page TOC Submit PCR GUITSTREAM IV MAINTENANCE MANUAL NO. PER UNIT LOCATION AJC CRT display cooling fan 2 Under cabin floor, FS 95, WL 81 - Left and right side Cockpit temperature sensor 1 Cockpit, FS 133 - Right side Left radio rack cooling fan 1 Left radio rack (floor level), FS 181 - 193 Air Data Computer (ADC) 2 Left and right radio rack Cabin differential pressure transducer 1 Right radio rack, FS 133 Cabin pressure power supply 1 Right radio rack, FS 133 Airflow sensor 1 Right radio rack (mounted to Right cooling fan) Outflow valve 1 Right radio rack, FS 140 - right side Safety valve 1 Right radio rack, FS 155 - right side Commutating module 1 Right radio rack, FS 158 - 169 Right radio rack cooling fan 1 Right radio rack, FS 158 - 169 Pressurization transducer 1 Right radio rack, FS 165 - right side Pressurization rate switch 1 Right radio rack, FS 181 - right side Cabin press warning (aneroid) switch 1 Right radio rack, FS 181 - left side Resistors 2 Main junction & relay box / panel (324/325) Cabin / cockpit temperature controller 2 Entrance compartment (FLR-15) L and R CRT commutating module 2 Under FLR-15, FS 158 -169 Cabin duct temp anticipator sensor 1 Under Baggage Floor, FS 527 (FLR-58) Cockpit silencer 2 Forward Cabin (FLR-22 and FLR-26) Cabin silencer 1 Aft Cabin (FLR-56) Cockpit duct temp anticipator sensor 1 Main Wheel Well, FS 452 Cabin temperature control sensor 2 Location determined by furnishing agency Cabin / cockpit face air duct check valve 2 Tail compartment, FS 580 - Left and right sides (1.5 in. diameter) Cabin / cockpit air duct check valve 2 Tail compartment, FS 580 - Left and right sides (3.0 in. diameter) Water separator anti-ice sensor 2 Tail compartment, FS 620 - Left and right sides Bypass duct assembly 2 Tail compartment, FS 620 - Left and right sides Water separator anti-ice valve 2 Tail compartment, FS 640 - Left and right sides Bleed air pressure transducer 2 Tail compartment, FS 650.75 - Left and right sides 21-00-00 Page 4 April 30/13 EFTA00609977 Title Page Prey Page Next Page TOC Submit PCR GULFSTREAM IV MAINTENANCE MANUAL NO. PER UNIT LOCATION AJC Primary heat exchanger 2 Tail compartment, FS 659 - Left and right sides Secondary heat exchanger 2 Tail compartment, FS 659 - Left and right sides Water separator cooling fan 2 Tail compartment, FS 659 - Left and right sides ACM bypass shut-off valve 2 Tail compartment, FS 659 (top) - Left and right sides ACM bypass check valve 2 Tail compartment, FS 659 - Left and right sides Servo air pressure regulator valve 2 Tail compartment, Approx. FS 660 - Left and right sides ACM compressor outlet overheat 2 Tail compartment, FS 665 (top) - Left and right sides Ram air check valve 1 Tail compartment, FS 666 - Left side Air cond shut-off and flow regulating valve 2 Tail compartment, FS 682.25 (top) - Left and right sides Cabin / cockpit ozone converter 2 Tail compartment, FS 705.625 - Left and right sides 3. Major Components A. Bleed Air Manifold The bleed air manifold is utilized as the source of hot compressed air for the air conditioning system. This air is available from one or both engines and APU or external air supply (on ground only). The bleed air manifold delivers air to using systems, one of which is the air conditioning system. The air is delivered at approximately 400°F and at a maximum of approximately 40 psig. This air is delivered to the air conditioning shut-off and flow regulating valves (hereafter known as the air conditioning shut-off valves) through T-fittings in the bleed air manifold located in the tail compartment. See Figure E B. Air Conditioning Shut-off and Flow Regulating Valve This valve can serve as a shut-off valve for the air conditioning system when system operation is to be terminated or as a flow regulator when air conditioning system is in operation. The valve is a pneumatically operated device with an internal electrical solenoid. As in all pneumatically operated valves in this system, upstream duct pressure is used as the operating force. The valve is a 2 1/2 inch normally open butterfly type device which incorporates as part of the assembly a servo, an actuator and a venturi body. See Figure al An internal shut-off electrical solenoid, when energized, ports operating air from the upstream side (bleed air manifold) of valve directly into diaphragm chamber and closes the valve. This prevents any air from entering the air conditioning system, thus operation of system is terminated. With a source of air in the bleed air manifold and shut-off solenoid de-energized, valve butterfly moves toward the open position and airflow through venturi body starts again. As this valve functions as a flow regulating device, airflow through the venturi portion of the valve, coupled with inlet air pressure, creates a differential across the differential pressure servo. This signal starts to modulate the valve butterfly toward the closed position. A second signal comes from the altitude bias servo 21-00-00 Page 5 April 30/13 EFTA00609978 Title Page Prey Page Next Page TOC Submit PCR GUI.FSTREAM IV MAINTENANCE MANUAL aneroid bellows, which adjusts the preload spring tension on the differential pressure servo, thereby causing airflow to be controlled commensurate with aircraft altitude (ambient barometric pressure). Electrical shut-off solenoid energizing will cause valve to be pressurized to the full close position. There are three ways to energize solenoid and close the valve: • Placing right or left PACK CONT switches OFF • On the ground, if discharge side of either ACM compressors reach 450°F (ground configuration only) • When crew depresses either ENGINE START selector switch to START position the left pack solenoid is energized when MASTER CRANK START switch is selected) • The RAM switch on cockpit overhead panel will close both air conditioning shut-off valves In all of the above, air conditioning must be terminated because of a malfunction of some component in the refrigeration system on ground. NOTE: As the various electrical circuits which control the air conditioning shut-off valves are involved with devices concerned with other parts of the system, these involvements will be covered later in this chapter. Refer to the Wiring Diagram Manual for electrical schematics. Downstream of air conditioning shut-off valve, the duct splits into two paths, one going to primary heat exchangers which is the first stage of cooling and the other forward to cabin and cockpit temperature control valves which is the bypass route. C. Temperature Control System From discharge side of the air conditioning shut-off valve, hot compressed air can take two available paths, through refrigeration unit or through temperature control valves. Amount of hot compressed air which will flow through the temperature control valves into outlet ducting is based on butterfly valve position. The remainder of hot compressed air from air conditioning shut-off valve must go through the refrigeration unit to be reduced in temperature and then rejoin the hot air downstream of temperature control valves in right proportion to become temperature controlled air. It is the position of temperature control butterfly valve which determines compartment temperature by mixing hot and refrigerated air to attain the desired compartment temperature. See Figure I3 In order to control compartment temperature, position of the appropriate temperature control valve must be varied accordingly. All temperature control devices in a system of this type are directed toward control of the temperature control valves. There are several units which comprise each valve system which will be discussed together. The temperature control valve system for cabin / cockpit consists of the following units: • 2 Cabin / cockpit temperature control valves • 2 Air pressure regulator valves • 2 Cabin / cockpit temperature controllers • 2 Cabin / cockpit temperature selectors • 1 Cockpit duct temperature sensor • 2 Cockpit temperature control sensors • 2 Cabin temperature control sensors • 1 Cabin duct temperature sensor • 2 Cockpit temperature sensors All of the above units have a function in operation of the temperature control valve as follows: (1) Cabin / Cockpit Temperature Control Valves Each of the two temperature control valves is a 2 inch diameter pneumatic modulating butterfly valve. The valve is normally closed. With no pneumatic pressure applied to its 21-00-00 Page 6 April 30/13 EFTA00609979 Title Page Prey Page Next Page TOC Submit PCR GUITSTREAM IV MAINTENANCE MANUAL diaphragm chamber, an internal spring mechanism will maintain butterfly in the closed position. The valve requires pneumatic pressure to open butterfly and the amount of opening may be controlled by varying pneumatic pressure applied. Each valve is controlled by pneumatic pressure which originates at a T-fitting upstream of the valve which comes from left or right servo control system respectively. Duct pressure is then routed to a device known as the servo pressure regulator valve. (2) Air Pressure Regulator Valves The air pressure regulator valves control pressure to the temperature control valves in accordance with a signal received from electrical control devices. The valve converts an electrical signal into a pneumatic signal. This pneumatic signal in turn positions the temperature control valve accordingly. The valve reflects information supplied to it from certain electrical control devices. The electrical control devices which supply the air pressure regulator valves with temperature information consist of 2 controllers, 4 thermostats and 2 anticipators. (3) Cabin / Cockpit Temperature Controllers The controller is a solid state box which interprets the various inputs and sends an electrical signal to the air pressure regulator valves. Input power for the air pressure regulator valve is from 28 V essential dc bus through appropriate circuit breakers and control switches. The crew exercises control over compartment temperature by manipulation of the selector rheostat located on the overhead panel in cockpit. Manually moving rheostat changes the resistance. This change is reflected back to the controller, therefore the crew has informed controller of desired temperature. Refer to the Wiring Diagram Manual for electrical schematic. See Figures Six temperature sensitive elements per system (2 cabin / cockpit temperature control sensors, 2 cabin / cockpit temperature sensor and 2 cabin / cockpit duct temperature anticipators sensors) supply additional information electrically to the cabin / cockpit temperature controller relating compartment temperature, duct temperature and temperature of air exhausted from the compartment involved. These factors are compared to desired temperature information from the selector rheostat and solid state controller then provides dc output signal to the air pressure regulator valves to control cabin / cockpit temperature control valves position. Additional functions of anticipator are to provide a rate of change control over the system and also to sense when duct temperature has reached a maximum allowable value. (4) Cabin / Cockpit Temperature Control Sensors The temperature sensors are dual elements consisting of two separate sections. One section provides temperature information to the cabin / cockpit temperature controllers, while the other element is actually a temperature bulb for the cabin air temperature indicator (digital) which is located in the overhead panel in cockpit. On Aircraft having ASC 162 a third sensor is added. It is used for temperature indication only. Refer to the Wiring Diagram Manual for electrical schematic. See Figures NOTE: The cabin / cockpit thermostats are identical parts. The thermostats are identical for interchangeability purposes. (5) Anticipators The anticipator elements consist of a triple thermistor sensing element whose connections terminate at a common disconnect. It is duct mounted downstream of the temperature control 21-00-00 Page 7 April 30/13 EFTA00609980 Title Page Prey Page Next Page TOC Submit PCR GUI.FSTREAM IV MAINTENANCE MANUAL valve in the temperature controlled air duct, but upstream of the actual compartment outlet. Refer to the Wiring Diagram Manual for electrical schematic. See Figure 5 The three independent sensing elements which comprise this unit are: • A lagged element which is provided with a thermal barrier (this is part of the rate of change circuit of controller) • An unlagged element which is directly exposed to airflow in duct (this is part of the rate of change circuit of controller) • A high limit element which is part of the duct temperature limiter circuit within controller The cabin and cockpit anticipators are identical, interchangeable units. Due to the fact that all three parts of element are hard wired into a common plug and common housing, a malfunction of any one of the three parts requires removal and replacement of entire unit. (6) Cockpit Temperature Sensor (Cockpit Only) This sensor consists of a single thermistor sensing element with a single disconnect providing the electrical connections. This unit works with the compartment thermostat to feed temperature information into controller. The cockpit sensor is located on FS 133 bulkhead, forward right side. (7) Temperature Control Valve Incorporated in aircraft air conditioning system is a crossover capability. In the event of major component failure, the crew can manually select the remaining operative system by placing L or R PACK CONT switch to OFF. If necessary, crew may place both systems off by selecting L and R PACK CONT switches to OFF. An explanation of the operation of this crossover function is as follows: (a) To pressurize both refrigeration units using both engines select L and R ENG BLEED AIR switches to ON. This will energize both bleed air pressure regulator and shut-off valves to open allowing bleed air pressure to be delivered to the air conditioning shut- off and control valves. Placing L and R PACK switches ON, bleed air pressure will be allowed to flow through these valves and to refrigeration units where air will be conditioned to desired temperature and delivered to cabin / cockpit. (b) In the event of loss of one engine, BLEED AIR switch for operating engine will be selected ON and inoperative engine BLEED AIR switch OFF. The ISOLATION switch will be placed in OPEN allowing the single engine to pressurize the whole bleed air manifold. To obtain full air conditioning, place L and R PACK switches ON. (c) In the event of loss of one refrigeration unit, select inoperative side OFF and ensure BLEED AIR switch of operating side is ON. Place TEMP CONTROL switch for operative side to ON and bleed air will be routed from engine through the air conditioning system shut-off and control valve through the operating refrigeration unit to cabin / cockpit. NOTE: Due to the crossover ducting, cabin overhead outlets on both sides will be operative. The main system supply lines also have a crossover duct allowing the main ducts to be operative during single pack operation. In addition to the source selection switches, there are two TEMP CONTROL knobs labeled AUTO-OFF-MANUAL that have variable temperature range settings from HOT to COLD. When in single pack operation only the temperature control valve of operating pack can be controlled. During dual pack operation cabin and cockpit temperatures are independently regulated. Cabin and cockpit temperatures may be monitored by digital read outs located directly above the TEMP CONTROL knobs. 21-00-00 Page 8 April 30/13 EFTA00609981 Title Page Prey Page Next Page TOC Submit PCR GUITSTREAM IV MAINTENANCE MANUAL D. Distribution System Downstream of the temperature control valves the hot compressed air which passed through the valves is joined by that portion of the air which was refrigerated. The hot and cold air are mixed downstream of the valves to become temperature controlled air. The cabin and cockpit having separate temperature control valves and distribution systems will be covered separately. The cockpit distribution system consists of the ducting from the cockpit temperature control valve, the refrigerated air duct, an air duct check valve, a silencer and four outlets in the cockpit. There are two controllable side (or shoulder) outlets and two noncontrollable foot outlets, one each on the pilot side and the copilot side. See Figure B The cabin distribution system consists of ducting from the cabin temperature control valve, refrigerated air check valve, a silencer and two baseboard shaped outlets running practically the entire length of the cabin on both sides. A fluted skirt near the floor level allows the air from the baseboard to enter the compartment. (1) Cabin and Cockpit Air Check Valves These are swing checks installed in the compartment ducting. They will only allow air to pass in a forward direction. Should the air attempt to reverse and pass in a rearward direction, valves would close preventing backflow. (2) Cabin and Cockpit Silencers Each compartment ducting incorporates a silencer installed under the floor for noise attenuation. These silencers are located as follows: • Cockpit silencer - approximately FS 219 to 255, forward section of cabin • Cabin silencer - approximately FS 498 to 534, aft section of cabin These silencers function to suppress the air noise coming from the engine bleed air ducts. E. Refrigeration System Bleed air not bypassing the temperature control valves is routed into the refrigeration section of aircraft. See Figure B This system consists of the following major components: • Primary heat exchanger • Air Cycle Machine (ACM) and ACM overtemp thermal switch • Secondary heat exchanger • ACM bypass check valve bypass duct assembly • Water separator anti-ice valve with associated sensor • Water separator unit Cooling is accomplished by two methods, heat exchangers and by an expansion turbine (air cycling machine). Dehumidification is accomplished by a mechanical water separator which is prevented from icing by means of an anti-ice system. (1) Primary Heat Exchanger The primary heat exchanger is the first stage of refrigeration. It utilizes ram air from the dorsal fin ram air inlet as a coolant. This is a single pass heat exchanger mounted on left and right sides of tail compartment. Just downstream of the outlet of the primary heat exchanger the duct takes a two way split, one duct going into the eye of compressor section of air cycle machine and the other bypassing the entire air cycle machine and secondary heat exchanger. This air passes through the water separator anti-ice valve into the anti-ice muff assembly. 21-00-00 Page 9 April 30/13 EFTA00609982 Title Page Prey Page Next Page TOC Submit PCR GUI.FSTREAM IV MAINTENANCE MANUAL (2) Air Cycle Machine (ACM) The ACM is an expansion turbine which reduces temperature by causing the air to perform useful work and in doing so causes a pressure and temperature drop. The work extracted from the airstream in the turbine section is absorbed by operating a compressor wheel which is directly shafted to the turbine wheel located in a separate chamber on the upstream side of the unit. A large percentage of the work which is extracted from the airstream by the turbine is used by the compressor wheel. As the compressor wheel is performing work on the upstream air its pressure and temperature are increased. This is called the bootstrap principle which is actually a pressure recovery system used in modern air cycle systems. With the ACM in full operation (no air going through the anti-ice valve), the airflow would be through the compressor section through the secondary heat exchanger into the nozzle of the turbine section. then out the eye of the turbine section into the mixing muff. The ACM check valve is provided to permit air flow around the compressor section of the ACM when pressure ratios are less than 1.0 It also prevents reverse flow when ratios are greater than one. This unit is a pneumatically actuated, spring-loaded closed, split flapper in line check valve. The valve is located in a 1.5 inch duct between the primary and secondary heat exchangers (between the ACM compressor inlet line and compressor outlet line). See Figure 0 NOTE: The following are recommended air conditioning pack operations using APU air: • On aircraft with air cycle machines P/N 2204700-01-01 through 2204700-4-1, operate both packs whenever APU is the bleed air source. • On aircraft with air cycle machines P/N 2204700-05-01 and subsequent, operate single pack as provided in this section. Operate right pack whenever APU is the bleed air source and engine starting will occur. Operate left pack whenever APU is the bleed air source and engine starting will not occur. These procedures will reduce the thermal transients on the APU turbine and reduce cabin pressure surges (bumps). (3) Secondary Heat Exchanger This is a single pass heat exchanger which is installed adjacent to the primary heat exchangers in the tail compartment, lett and right sides. This heat exchanger also utilizes ram air from the dorsal fin ram air inlet as a coolant. (4) Cooling Fan Ground air conditioning presents additional requirements to the system. On the ground there is no ram air, thus no coolant airflow across primary and secondary heat exchangers. This airflow must be supplied, otherwise the refrigeration equipment will overheat. In addition there are times when air conditioning system operation must be terminated due to high demands from bleed air manifold, such as during engine starts. Being a self-supporting aircraft it must be capable of being air conditioned by use of the APU even if main engines are not operating. With few exceptions, airflow through the system when in ground operation is the same from the bleed air manifold to the compartment outlets. The essential difference is in the source of ram airflow for heat exchangers. This is accomplished through a 3-bladed axial flow fan which is an integral component of the ACM. It is physically attached to a common shaft with the compressor and turbine wheels of the ACM and rotates in consonance with them. It provides cooling air flow across the primary and secondary heat exchanges whenever the air conditioning unit is in operation. Air for cooling is delivered through the dorsal fin ram air inlet inflight and through that inlet plus a flapper door in the refrigeration unit ducting on the ground. All air is then ported overboard. The cooling fan cannot be individually controlled. 21-00-00 Page 10 April 30/13 EFTA00609983 Title Page Prey Page Next Page TOC Submit PCR GILHISTREAM IV MAINTENANCE MANUAL (5) ACM Bypass Shut-off Valve Included in the Environmental Control System (ECS) are two ACM bypass shut-off valves and associated ducting. The ACM bypass shut-off valves are 1.5 inch nominal diameter valves which allow airflow around the turbine section of the ACM whenever open. The unit receives its signals from the air data computer which opens valves at an altitude of 42,000 feet or greater and closes valves at an altitude of 40,000 feet or less. The valve is spring-loaded to close in event of failure. The valve contains a visual position indicator and a relief regulator for actuator overpressure protection. See Figure g When the solenoid valve is energized, inlet air upstream of the valve's butterfly valve is admitted to the actuator diaphragm. When this pressure overcomes the spring force, the butterfly valve moves to the open position. When the solenoid valve is de-energized, actuator pressure is vented through the solenoid valve allowing the actuator spring to close the butterfly valve. F. Water Separator System Expansion through the cooling turbine reduces discharge temperatures below ambient temperatures and the low discharge temperature forces moisture in the air to condense. This moisture would produce high humidity and greatly lessen passenger comfort if not removed. The water separator provides a mechanical means of water removal and consists of two sections. The inlet section is a coalescer (meaning "to cause to come together). It makes a few large drops from many small droplets by passing the moisture laden airstream through a coarse mesh cloth bag and a set of swirl vanes. The airstream is forced to swirl or spin so that the large drops are spun to the outside walls by centrifugal force, where they are collected by the second section, or collector and deposited into the water separator sump. From the sump, water taken out of the air is plumbed to the secondary heat exchanger through a water spray aspirator (single stage jet pump) to assist in cooling the air. The separator is capable of removing approximately 80% of all water passing through it, including water vapor. The water separator also contains a relief valve, which, if the cloth coalescer bag is clogged, will bypass the air through the unit. In this case, dehumidification will not take place. G. Water Separator Anti-Ice System Normally, cooling turbine discharge temperatures fall low enough so that water is not only condensed, but will freeze. To prevent the coalescer bag of the water separator from becoming clogged with ice crystals and restricting airflow. a water separator anti-ice system is installed. The system consists of the water separator anti-ice valve (anti-ice air modulating valve), and a combination anti-ice sensor and controller. The components are located in the tail compartment. See Figure S As can be seen from Figure ❑1 or Figure E the anti-ice valve will bypass extremely warm primary heat exchanger air around the ACM and secondary heat exchanger when open. This air