Technologies of the aircraft systems refilling by the special gases

Лабораторная работа

Астрономия и авиация

Brief theoreticl dt The onbord ircrft systems re refilled by the following specil gses: medicl oxygen for brething of crew nd pssengers in the cse of cockpit depressuriztion; nitrogen is refilled in chmbers of shock bsorbers of lnding ger gseous chmbers of hydrulic ccumultor tnks superchrging system for the hydrulic system nd fuel system; compressed ir for refilling in chmbers of shock bsorbers of lnding ger nd wheels tires. Refilling of the onbord ircrft systems by medicl oxygen is the most difficult nd dngerous technologicl...



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Laboratory work 1.3.

Technologies of the aircraft systems refilling by the special gases

The purpose of work is to study the equipment and feature of its application technology for refilling the on-board aircraft systems by the compressed gases, and also accident precaution issues.

Brief theoretical data

The on-board aircraft systems are refilled by the following special gases:

- medical oxygen for breathing of a crew and passengers in the case of cockpit depressurization;

- nitrogen is refilled in chambers of shock absorbers of landing gear, gaseous chambers of hydraulic accumulator, tanks supercharging system for the hydraulic system and fuel system;

- compressed air for refilling in chambers of shock absorbers of landing gear and wheels tires.

For these purposes both towed and self-propelled gas refilling units are intended for replenishment of the special gases stocks of the on-board aircraft system.

Example of simplest towed gas refilling unit containing on the cart two gas cylinders and compressor plant is shown on the fig. 1.3.1.

Refilling of the on-board aircraft systems by medical oxygen is the most difficult and dangerous technological procedure, therefore let’s consider the most general case and design of self-propelled motor-car oxygen refilling unit.

Intention, design and operation of the unit (oxygen truck)

The motor-car oxygen refilling unit АКЗС-75М-131-III is intended for refilling by the medical oxygen of the on-board systems of aircraft.

The system and equipment of unit allow:

- refilling an own bank of gas cylinders of the unit by oxygen from the external sources to filling pressure of 15,0 MPa   (150 kg/sm2);

- refilling aircraft on-board gas cylinders, and also transportable gas cylinders from bank of unit to filling pressure of 15,0 MPa  (150 kg/sm2);

- refilling parachute devices to pressure 15,0 MPa (150  kg/sm2);  

- refilling on-board and transportable gas cylinders of low pressure through the reducing valve to pressure 3,0 MPa (30 kg/sm2);

- transferring the oxygen from one gas cylinders group of unit in other with purpose of the most complete use of it.

The unit is related with group of fire-hazardous objects, which require the observance of necessary precautionary actions.

A unit is the compressor plant (fig. 1.3.2., 1.3.3., 1.3.4), mounted on the ЗИЛ truck chassis. A compressor drive is carried out from the truck engine by two cardan shafts through the power take-of gearbox and intermediate support.

All equipment of unit is mounted in the rigid metallic carbody. A carbody is removable, divided by partition on three compartments: compressor, gas cylinder and compartment for placing of the assemblies of the fire-control system.

The compressor compartment has two hatches, placed on the rear wall of carbody - one opens a control panel, and second is entrance door in the compressor compartment. From the right side of compartment there is a hatch for placing a refilling hose.

The gas cylinder compartment of carbody has folding hatches for access to the valves of gas cylinders and to the spare parts and expendables of the unit.

In the compressor compartment the unit pressurizing compressor КП-75М, gear of rotary speed control, system of the oxygen cooling, dehydrator, warming up system, control panel with the oxygen communication are placed.

In the gas cylinder compartment of unit 21 transportable gas cylinders are placed. Gas cylinders are located in three lines and connected by communication in three horizontal group. All assemblies of the fire-control system of unit are placed in the fire-prevention compartment: pneumatic actuator, the РПУ-2 relay switch, two fire-extinguishers of ОС-8М and three cut off valves.

In case of unit preparation to operation, refilled gas cylinders, at first are filled with oxygen in the way of crossover delivery. Then there is topping-up of gas cylinders by boosting of oxygen using the КП-75М compressor to evolving of final pressure in the refilled gas cylinders upto 15,0 MPa.

Technical specifications of АКЗС-75М-131- III unit

Truck chassis..................................................ЗИЛ-131

Mass of loaded in unit, kg....................................9170

Performance, м3/hour.......................................................75

Total stock of oxygen, м3....................................157

Quantity of gas cylinders, pcs………....................21

Capacity of gas cylinders, м3(л).....................0,05 (50)

Pressure in gas cylinders, MPa (kg/sm2).........................1(150)

Compressor type.............................................КП-75М horizontal, plunger, double cylinder

Fig. 1.3.2. External view of the АКЗС-75М-131- III oxygen truck.

Fig. 1.3.3. Top view of unit in sectioning:

1 – hose distributing-refilling; 2 – dehydrator; 3 – system of warming up; 4 – cooler assembly; 5 – the КП-75М compressor; 6 – gear of rotary speed control; 7 – control panel; 8 – fire-prevention system; 9 – electrical equipment; 10 – oxygen gas cylinders; 11 – rear cardan shaft; 12 – intermediate support; 13 – front cardan shaft; 14 – power take-off gear box.

Fig. 1.3.4. Side view of unit in sectioning:1 – oxygen gas cylinders; 2 – cooler assembly; 3 – dehydrator; 4 – the КП-75М compressor; 5 – intermediate support; 6 – cardan shaft; 7 – power take-off gear box.

Compressor rotary speed, rps (rpm)..............4,6–5,0 (280-300)

Compression ratio of compressor............................................3

Duration of continuous operation (by compressor), hour.......1

Cooling oxygen......................................................................air

Type of exsiccant (desiccant)......................zeolite or silica gel                             

Overall dimensions, mm:




Maximal time of unit deployment in the working configuration, min........................45

2. Equipment of the АКЗС-75М-131-III unit

The unit consists of:

- pressurizing compressor  КП-75М;

- systems of the compressor lubrication;

- compressor drive;

- compressor rotary speed control gear;

- systems of warming up of compressor lubricant;

- systems of the oxygen cooling;

-  oxygen dehydration systems;

- control panel with the oxygen communication and accessories;

- fire-prevention systems;

- electrical equipment systems of unit.

3. Design and operation of component parts of unit

3.1 Pressurizing compressor КП-75М.

Compressor is intended to pump over and pressurize the oxygen in the refilled gas cylinders. Basic units of compressor (fig. 1.3.5., 1.3.6.): casing, crank shaft, cylinders jackets, rod, plungers, insert, cylinders heads, intake and outlet valves, fly-wheel.

Compressor motion gear is swinging arm link. In case of rod motion to the left in the right cylinder underpressure is created and through the intake valve oxygen is sucked in. Meanwhile in the left cylinder there is a squeezing of oxygen, and when the pressure in cylinder achieves a greater size, than pressure behind the outlet valve, it is opened and oxygen is pumped in communication pipeline. In case of rod back motion a reverse process takes place. The complete cycle of suction, squeezing and pumping the oxygen in both cylinders takes place in one turn of crank shaft. For the more smooth operation on the compressor shaft a fly-wheel is installed.

Technical specifications of compressor.

Compressor type........... pressurizing, double cylinder, single-stage

Working pressure, MPa..........................................15,0(150)

Compression ratio....................................................................3

Rotary speed, rps (rpm).........................................4,6-5,0 (820-300)

Cylinder diameter, mm............................................................30

Piston motion, mm...............................................60

Lubrication of the motion gear......................................glycerin

Fig. 1.3.5. The КП-75М compressor (longitudinal sectioning): 1 - fly-wheel; 2 - crank shaft; 3,4 - plugs; 5 - upper window (lid); 6 - rear window; 7 - casing; 8 - rod; 9 - drain cork

Fig. 1.3.6. The КП-75М compressor (sectioning along the valves): 1 - suction pipeline; 2 - intake valve; 3 - insert; 4,9 - jackets of cylinders; 5 - casing; 6 - manifold; 7 - rod; 8 - heat exchanger; 10 - outlet valve; 11 - pressure pipeline; 12 - cylinder head

3.5 System of the oxygen cooling

A cooling system assembly is intended for oxygen cooling (fig. 1.3.7.), which is delivered from compressor. It is a three line worm-pipe, which is blown around by air. It is made of the copper pipes with diameter of 9х5 mm. Blowing is performed by the fan, fastened on the compressor fly-wheel.  The air, blowing pipes, goes out through opening in fan sump.

Fig. 1.3.7. Oxygen air-cooling system: 1 - block of worm-pipes; 2 - fan; 3 - fly-wheel; 4 – sump

3.6 Oxygen dehydration system

A dehydration (fig. 1.3.8. and 1.3.9.) block is intended for the removal the moisture from oxygen, which went in it as a result of contact with the water-glycerin mixture during compressor work. A block consists of moisture separator and dehydrator.

Moisture separator (fig. 1.3.9.) is intended for the separation the drip moisture from oxygen. Working principle of moisture separator is following. Oxygen from cooler through connector is delivered in moisture separator on the bent guiding pipe. In case of passing through the moisture separator stream of oxygen begins to be revolved, and moisture parts under action of centrifugal force and speed change


Fig. 1.3.8. Dehydration block: 1 – moisture separator; 2 – dehydrator

Fig. 1.3.9. Moisture separator: 1 – connector; 2 – giuding pipe; 3 – central pipe; 4 – casing

are settled on the casing walls and then flow down in the lower part of vessel. Moisture which was accumulated in the casing bottom is periodically removed through the scavenge valve. The oxygen through the central pipe of moisture separator is delivered in dehydrator.

On unit two identical design dehydrators are installed (fig. 1.3.10.), and connected parallel. Dehydrator is intended for absorption of water vapors, which had been remained in oxygen after passing through moisture separator. It is a steel vessel of 5 liters capacity, filled by zeolite (СаА or Na grades according to МРТУ 6-01-906-66). A connector is screwed in on the inlet of oxygen in dehydrator with the reticulated filter, on the oxygen outlet from the dehydrator a ceramic filter is mounted with filtration fineness of 100±20 micrometers.

Fig. 1.3.10.  Dehydrator: 1 – steel vessel; 2 - flange; 3 - reticulated filter; 4 - ceramic filter; 5 – nut.

Dehydrator functioning is based on the high adsorption power, that is on its property well absorption of the water vapors, which are in gases. In course of time a zeolite is gradually moistened, its adsorption properties are worsened. However the wet zeolite after roasting recovers its adsorption properties and can again well absorb the moisture.

Regeneration of a moistened zeolite is performed in the drying oven of the Ш-0,05 type at temperature +300-350 °C in 4,5-5,5 hours.

3.7 Control panel with the oxygen communication and equipment

A control panel is mounted in the compressor compartment in the carbody rear part and is closed by the special cover. Valves and pressure gauges of oxygen communications, switches and warning lamp are mounted on the right side of panel. On back side of panel oxygen communications and wiring are mounted.

The communications mounted on the control panel depending on its destination are subdivide on the following pipelines (fig. 1.3.11.):

a) suction pipeline is from the inlet valves of compressor to the suction valves on the control panel.(Suction of oxygen is performed by this pipeline, valves of this pipeline are marked by the numbers 6, 14, 21);

b) delivery pipeline is from the outlet valves of compressor to the delivery valves on the control panel. (Pumping of oxygen is performed by this pipeline. Within the delivery line refrigerator, moisture separator, two dehydrators and safety-valve are located. Valves of delivery pipeline are marked by the numbers 5, 13, 20);

c) distributive pipeline is to the outlet valves on the control panel to the connector of distribution-refilling through the valve 22;

d) refilling pipeline is from refilling-distribution connector to the suction valves on the control panel through the valve 24.

Pressure in the delivery pipeline is determined by the pressure gauge with table "refilling pressure", in the suction pipeline – by pressure gauge with table "suction pressure". Indications of these pressure gauges are duplicated by indications of pressure gauge of gas cylinders banks.

The unit circuit allows pumping over the oxygen from one bank of gas cylinders into another. So, for example, with the opened valves 14 and 20 the compressor will suck in oxygen by the suction pipeline from gas cylinders of the second bank, and deliver it through the delivering pipeline in gas cylinders of the third bank.

The suction and delivery pipelines are united between themselves by the valve of the closed cycle 16. This valve is used, when we need temporally to cease pumping over oxygen, not stopping a compressor. In this case a valve 18 is opened and some valve of supplying group, for example 21. The oxygen will be then sucked in by compressor from gas cylinders of the third bank by the suction pipeline and through the delivery pipeline and valve 18 will return back, that is there will be the closed cycle without the pressure rise in pipeline.

The valve 22 of distributive pipeline is intended for the delivery of oxygen to the distributing connector.

A suction pipeline is connected with the delivery pipeline using the valve 24.

Fig.1.3.11. Principle chart of oxygen communication of unit

On the suction and delivery pipelines near the distributing connector check valves 29 and 30 are installed, that allow oxygen to flow in one direction only.

From the delivery pipeline the branch goes through valve 23 to the reducing valve, which reduces the pressure to 3,0 MPa. Using this reducing valve refilling of low pressure gas cylinders to 3,0 MPa can be executed. Reduced pressure is monitored by pressure gauge 27 on the control panel.

For oxygen discharge from communication in atmosphere the valves 17 and 25 are used. The scavenge valve 17 is also intended for the periodic removal of moisture, which was flowing in bottom of moisture separator.

Scavenging is performed by pipeline that is led out under the unit carbody. Refilling a unit and distribution of oxygen is conducted through the same connector 28.

A control panel (fig. 1.3.12.) panel is made from the steel sheet. All measuring devices and regulation valves are located on the panel. Valves are located in the first line 3 and 5 of oxygen reducing valve. Between valves the clock 4. is located

Three pressure gauges are located in the second line 2, showing pressure in three banks of gas cylinders and two pressure gauges, which show pressure in delivery 6 and in suction in 7 pipelines. On the right of them there is a pressure gauge of reducing valve 8, on the left - indicator of distance thermometer 1, showing a glycerin temperature in compressor casing.

Fig. 1.3.12.  Control panel:

1 - indicator of distance thermometer; 2,6,7 - pressure gauges; 3,5 - valves of distribution in 3,0 MPa; 4 - clock; 8 - pressure gauge of reducing valve; 9,11 – stop valve; 10 - valve of distribution in 15,0 MPa; 12 - valves of the first bank; 13 - valve of the second bank; 14 - valves of the third bank; 15 - valve of closed cycle;  16 - valve of refilling in 15,0 MPa; 17 - valve of hose scavenging; 18 - safety-valve; 19 - tables; 20 - indicator lamp of the fire prevention system; 21 - button of a compressor starting up; 22 - switch of a clock warming up; 23 - button of the engine emergency shut down; 24 - compressor illumination switch; 25 - compressor stop button; 26 - panel illumination switch; 27 - indicator of compressor rotary speed

In the third line under pressure gauges of bank of gas cylinders three valves are located: 12, 13, 14 delivery pipeline. On the right of them - stop valve 9, allowing during work on the closed cycle to block access of gas to dehydrators; valve 10 distribution in 15 MPa and valve 11 of moisture separator scavenging.

In the fourth line under valves of the delivery pipeline 12, 13 and 14 valves of suction pipeline are located. To the right from them there is a valve 15 closed cycle, refilling valve 16 of unit gas cylinders in 15 MPa and valve 17 of hose scavenging.

Under fourth line the buttons are alongside located 21 and 25 warning about the start up and shutdown of compressor and button of 23 emergency shutdown of engine, to the right from them - device 27, showing a compressor rotary speed.

At the bottom of the panel a switch of a clock warming up is located 22, compressor illumination switches 24 and panel 26, control lamp 20 of fire prevention system.

Under every device a table, which specifies the name of given device is placed.

On the control panel also four more tables are placed:

- first and second - with instructions about the observance of precautionary measures on unit;

- third - with circuit of oxygen communication;

- fourth – with table of oxygen pressure dependence in gas cylinders from the ambient temperature.

Labour precaution rules during operation of

oxygen truck

On-board oxygen systems regardless of their destination are to be refilled only by the medical oxygen.

In avoidance of refilling hoses explosion application of the depreservated and not degreased oxygen hoses is forbidden.

Oxygen gas cylinders where the pressure will turn out equal to atmospheric are admitted to the further application only after the twin-thrice-repeated washing by oxygen with the following refilling them to the nominal pressure.

Oxygen and other equipment, which contains pressurized gases, is allowed to application, if it completely in good state and is tested by institutions of State Inspectorate.

Repair of equipment which contains pressurized gases is allowed only after the gas discharge with the observance of precautionary issues, foreseen by instruction.

With purpose of prevention of inflammation and explosion in the oxygen compressors, receivers and accesories you should:

- apply for lubrication of oxygen compressors only those lubricating materials, which are recommended by factories-manufacturers (glycerin, water-glycerin  mixture etc.).

- take the avtions for prevention of contamination of oxygen devices by oil and greasings, do not approach to such equipment with the fatty wiping materials and in the dirty overall;

- check impermeability of oxygen equipment using the soapy water, not using smouldering objects;

- execute procedures with the oxygen equipment in the clean, without the oily stains, overall, by degreased tools;

- on leaving from environment, saturated by oxygen, to ventilate an overall and hairs for the oxygen removal; at that do not approach to the fire and smoke, for prevention of self-ignition of clothes and hairs;

Application of mineral oils for lubrication of oxygen compressors and usage of oxygen truck without earth bonding circuit is forbidden.



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