What Is Used To Flush A System Normally Serviced With Mil-h-5606 Hydraulic Fluid?

To assure proper organization performance and to avert damage to nonmetallic components of the hydraulic system, the correct fluid must exist used. When calculation fluid to a system, use the type specified in the shipping manufacturer'south maintenance manual or on the instruction plate affixed to the reservoir or unit being serviced.

The iii chief categories of hydraulic fluids are:

Minerals
Polyalphaolefins
Phosphate esters

When servicing a hydraulic system, the technician must exist certain to use the correct category of replacement fluid. Hydraulic fluids are not necessarily compatible. For example, contagion of the fire-resistant fluid MIL-H-83282 with MIL-H-5606 may render the MIL-H-83282 non fire-resistant.

Mineral-Based Fluids

Mineral oil-based hydraulic fluid (MIL-H-5606) is the oldest, dating back to the 1940s. It is used in many systems, specially where the fire run a risk is comparatively low. MIL-H-6083 is but a rust-inhibited version of MIL-H-5606. They are completely interchangeable. Suppliers generally transport hydraulic components with MIL-H-6083. Mineral-based hydraulic fluid (MIL–H-5606) is processed from petroleum. It has an odor similar to penetrating oil and is dyed ruddy. Constructed safety seals are used with petroleum-based fluids.

Polyalphaolefin-Based Fluids

MIL-H-83282 is a burn-resistant hydrogenated polyalphaolefinbased fluid developed in the 1960s to overcome the flammability characteristics of MIL-H-5606. MIL-H-83282 is significantly more flame resistant than MIL-H-5606, but a disadvantage is the high viscosity at low temperature. It is generally limited to –40 °F. However, it can exist used in the aforementioned system and with the same seals, gaskets, and hoses as MIL-H-5606. MIL-H-46170 is the rust-inhibited version of MIL-H-83282. Pocket-size shipping predominantly apply MIL-H-5606, but some have switched to MIL-H-83282 if they tin accommodate the loftier viscosity at low temperature.

Phosphate Ester-Based Fluid (Skydrol®)

These fluids are used in most commercial transport category aircraft and are extremely fire-resistant. Yet, they are not fireproof and under certain weather condition, they burn. The earliest generation of these fluids was developed after Earth State of war II equally a result of the growing number of aircraft hydraulic restriction fires that drew the commonage concern of the commercial aviation manufacture. Progressive development of these fluids occurred equally a result of performance requirements of newer aircraft designs. The airframe manufacturers dubbed these new generations of hydraulic fluid every bit types based on their performance.

Today, types Four and V fluids are used. Two distinct classes of type IV fluids exist based on their density: form I fluids are low density and class II fluids are standard density. The grade I fluids provide weight savings advantages versus course II. In addition to the blazon IV fluids that are currently in use, type V fluids are being adult in response to manufacture demands for a more thermally stable fluid at higher operating temperatures. Blazon V fluids will be more than resistant to hydrolytic and oxidative degradation at high temperature than the blazon Four fluids.

Intermixing of Fluids

Due to the departure in limerick, petroleum-based and phosphate ester-based fluids will not mix; neither are the seals for any one fluid usable with or tolerant of any of the other fluids. Should an aircraft hydraulic arrangement be serviced with the incorrect blazon fluid, immediately drain and flush the system and maintain the seals co-ordinate to the manufacturer'southward specifications.

Compatibility with Aircraft Materials

Aircraft hydraulic systems designed around Skydrol® fluids should exist well-nigh trouble-free if properly serviced. Skydrol® is a registered trademark of Monsanto Company. Skydrol® does non appreciably affect common aircraft metals—aluminum, silverish, zinc, magnesium, cadmium, iron, stainless steel, bronze, chromium, and others—as long as the fluids are kept gratuitous of contamination. Due to the phosphate ester base of Skydrol® fluids, thermoplastic resins, including vinyl compositions, nitrocellulose lacquers, oil-based paints, linoleum, and asphalt may be softened chemically by Skydrol® fluids. Withal, this chemical action usually requires longer than just momentary exposure, and spills that are wiped up with soap and h2o do not impairment most of these materials. Paints that are Skydrol® resistant include epoxies and polyurethanes. Today, polyurethanes are the standard of the aircraft industry because of their power to keep a bright, shiny finish for long periods of time and for the ease with which they tin be removed.

Hydraulic systems require the use of special accessories that are uniform with the hydraulic fluid. Appropriate seals, gaskets, and hoses must be specifically designated for the type of fluid in utilise. Care must exist taken to ensure that the components installed in the system are compatible with the fluid. When gaskets, seals, and hoses are replaced, positive identification should be made to ensure that they are made of the appropriate material. Skydrol® blazon V fluid is compatible with natural fibers and with a number of synthetics, including nylon and polyester, which are used extensively in almost shipping. Petroleum oil hydraulic system seals of neoprene or Buna-North are not uniform with Skydrol® and must be replaced with seals of butyl rubber or ethylene-propylene elastoiners.

Hydraulic Fluid Contagion

Feel has shown that trouble in a hydraulic organization is inevitable whenever the liquid is allowed to become contaminated. The nature of the problem, whether a simple malfunction or the complete destruction of a component, depends to some extent on the blazon of contaminant. Two general contaminants are:

Abrasives, including such particles as core sand, weld spatter, machining fries, and rust.
Nonabrasives, including those resulting from oil oxidation and soft particles worn or shredded from seals and other organic components.

Contamination Check

Whenever it is suspected that a hydraulic system has become contaminated or the system has been operated at temperatures in backlog of the specified maximum, a check of the system should exist made. The filters in most hydraulic systems are designed to remove most foreign particles that are visible to the naked middle. Hydraulic liquid that appears clean to the naked eye may be contaminated to the point that it is unfit for use. Thus, visual inspection of the hydraulic liquid does not determine the full corporeality of contamination in the arrangement. Large particles of impurities in the hydraulic system are indications that one or more components are existence subjected to excessive wear. Isolating the defective component requires a systematic process of elimination. Fluid returned to the reservoir may contain impurities from any role of the arrangement. To determine which component is defective, liquid samples should exist taken from the reservoir and various other locations in the organisation. Samples should exist taken in accordance with the applicable manufacturer's instructions for a particular hydraulic system. Some hydraulic systems are equipped with permanently installed bleed valves for taking liquid samples, whereas on other systems, lines must be asunder to provide a place to have a sample.

Hydraulic Sampling Schedule

Routine sampling—each system should be sampled at least once a year, or every 3,000 flight hours, or whenever the airframe manufacturer suggests.
Unscheduled maintenance—when malfunctions may accept a fluid related cause, samples should be taken.
Suspicion of contamination—if contagion is suspected, fluids should exist drained and replaced, with samples taken before and afterward the maintenance process.

Sampling Procedure

Pressurize and operate hydraulic system for 10–fifteen minutes. During this period, operate diverse flight controls to activate valves and thoroughly mix hydraulic fluid.
Shut down and depressurize the system.
Before taking samples, always exist certain to wear the proper personal protective equipment that should include, at the minimum, prophylactic glasses and gloves.
Wipe off sampling port or tube with a lint-free fabric. Do not use shop towels or paper products that could produce lint. More often than not speaking, the human middle can run across particles down to about 40 microns in size. Since we are concerned with particles down to 5 microns in size, it is easy to contaminate a sample without ever knowing it.
Identify a waste material container nether the reservoir bleed valve and open up valve and so that a steady, but not forceful, stream is running.
Let approximately 1 pint (250 ml) of fluid to drain. This purges whatsoever settled particles from the sampling port.
Insert a precleaned sample canteen under the fluid stream and fill, leaving an air space at the top. Withdraw the canteen and cap immediately.
Close drain valve.
Fill out sample identification label supplied in sample kit, making sure to include customer proper name, aircraft type, aircraft tail number, hydraulic system sampled, and date sampled. Point on the sample label under remarks if this is a routine sample or if it is being taken due to a suspected problem.
Service system reservoirs to replace the fluid that was removed.
Submit samples for analysis to laboratory.

Contagion Control

Filters provide adequate control of the contamination problem during all normal hydraulic system operations. Command of the size and amount of contagion entering the system from whatsoever other source is the responsibility of the people who service and maintain the equipment. Therefore, precautions should be taken to minimize contamination during maintenance, repair, and service operations. If the arrangement becomes contaminated, the filter element should be removed and cleaned or replaced. As an help in decision-making contamination, the following maintenance and servicing procedures should be followed at all times:

Maintain all tools and the work area (workbenches and test equipment) in a clean, dirt-free condition.
A suitable container should ever be provided to receive the hydraulic liquid that is spilled during component removal or disassembly procedures.
Before disconnecting hydraulic lines or fittings, make clean the affected area with dry cleaning solvent.
All hydraulic lines and fittings should be capped or plugged immediately afterward disconnecting.
Before assembly of any hydraulic components, wash all parts in an approved dry cleaning solvent.
After cleaning the parts in the dry cleaning solution, dry out the parts thoroughly and lubricate them with the recommended preservative or hydraulic liquid before associates. Use only clean, lint-free cloths to wipe or dry the component parts.
All seals and gaskets should be replaced during the reassembly process. Use only those seals and gaskets recommended by the manufacturer.
All parts should be connected with intendance to avoid stripping metallic slivers from threaded areas. All fittings and lines should be installed and torqued in accord with applicable technical instructions.
All hydraulic servicing equipment should be kept make clean and in good operating condition.

Contamination, both particulate and chemical, is detrimental to the performance and life of components in the aircraft hydraulic system. Contamination enters the system through normal habiliment of components by ingestion through external seals during servicing, or maintenance, when the arrangement is opened to replace/repair components, etc. To control the particulate contamination in the system, filters are installed in the pressure line, in the return line, and in the pump example drain line of each system. The filter rating is given in microns equally an indication of the smallest particle size that is filtered out. The replacement interval of these filters is established by the manufacturer and is included in the maintenance manual. In the absenteeism of specific replacement instructions, a recommended service life of the filter elements is:

Pressure filters—3,000 hours
Return Filters—one,500 hours
Case drain filters—600 hours

Hydraulic System Flushing

When inspection of hydraulic filters or hydraulic fluid evaluation indicates that the fluid is contaminated, flushing the system may be necessary. This must be done according to the manufacturer'southward instructions; nevertheless, a typical procedure for flushing is equally follows:

Connect a ground hydraulic test stand up to the inlet and outlet test ports of the arrangement. Verify that the basis unit of measurement fluid is clean and contains the aforementioned fluid every bit the aircraft.
Modify the system filters.
Pump clean, filtered fluid through the system, and operate all subsystems until no obvious signs of contamination are establish during inspection of the filters. Dispose of contaminated fluid and filter. Annotation: A visual inspection of hydraulic filters is not e'er constructive.
Disconnect the test stand and cap the ports.
Ensure that the reservoir is filled to the full line or proper service level.

It is very important to cheque if the fluid in the hydraulic test stand, or mule, is clean before the flushing operation starts. A contaminated hydraulic examination stand up can speedily contaminate other aircraft if used for ground maintenance operations.

Health and Handling

Skydrol® fluids are phosphate ester-based fluids blended with performance additives. Phosphate esters are good solvents and deliquesce away some of the fat materials of the pare. Repeated or prolonged exposure may cause drying of the skin, which if unattended, could result in complications, such as dermatitis or even secondary infection from bacteria.

Skydrol® fluids could cause itching of the pare but have non been known to crusade allergic-type pare rashes. Always utilize the proper gloves and centre protection when treatment whatsoever blazon of hydraulic fluid. When Skydrol®/Hyjet mist or vapor exposure is possible, a respirator capable of removing organic vapors and mists must be worn. Ingestion of any hydraulic fluid should be avoided. Although small amounts exercise non appear to be highly hazardous, whatever pregnant amount should exist tested in accord with manufacturer's direction, followed with hospital supervised stomach handling.

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