Advantages of Hydraulics

Compared with mechanical transmission, electrical transmission, hydraulic transmission has the following advantages.

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1. hydraulic transmission of various components, can be easily and flexibly arranged according to the needs.

2. light weight, small size, small inertia of movement, fast response time.

3. easy to manipulate and control, can achieve a wide range of stepless speed regulation (speed range up to :1).

4.Overload protection can be realized automatically.

5. generally using mineral oil as the working medium, the relative moving surface can be self-lubricated, long service life.

6.It is easy to realize linear motion

7. it is easy to realize the automation of the machine, when using electro-hydraulic joint control, not only can realize a higher degree of automatic control process, but also can realize remote control.

Disadvantages of Hydraulic Pressure

Here are some disadvantage of hydraulic:

1.The efficiency is low because of the resistance of fluid flow and the large leakage. If not handled properly, the leakage not only pollutes the site, but also may cause fire and explosion accidents.

2.Since the working performance is easily affected by temperature changes, it is not suitable to work under very high or very low temperature conditions.

3.The manufacturing precision of hydraulic components is required to be high, thus more expensive.

4. because of the liquid medium leakage and compressibility, can not get a strict transmission ratio.

5. hydraulic transmission failure is not easy to find the cause; use and maintenance requires a high level of technology.

Joint Installation

The hose shall not be over-bent in moving or at rest, nor shall it be bent at the root, but at least at 1.5 times its diameter.

the hose shall not be pulled too tightly when moving to the extreme position, and shall be relatively slack.

avoid twisting deformation of the hose as much as possible.

the hose should be kept as far away as possible from heat-emitting elements, with insulation plates if necessary

External damage to the hose should be avoided, such as long-term friction with the surface of the components in use.

If the self-weight of the hose causes excessive deformation, there should be support pieces.

Piping installation

All hydraulic pipes can be acid cleaned before installation, especially the steel pipes connected with pipe fittings should be acid cleaned first, and then the ferrules should be fastened in the pipe end in advance.

All pipe joints should be cleaned with kerosene before installation, and the o-ring inside should be temporarily removed for storage and put on again when formally installed.

During construction, keep the oil ports of hydraulic pumps, distributors and other equipment, pipe joints, pipe ends and other openings clean, and do not allow water, dust and other foreign objects to enter.

The pipeline should be laid in a free state, and the welded pipeline should not be forcibly fixed and connected by exerting excessive radial force.

The oil hole of the bearing seat should be checked in advance, whether the internal oil circuit is smooth and whether the thread of the oil port matches with the joint.

Pipeline Cleaning

In order to ensure that the lubrication system is clean, and supply the bearings of machinery and equipment with clean grease, the pre-installed pipeline must be removed and cleaned. There are two kinds of cleaning: kerosene cleaning and acid cleaning.

Kerosene Cleaning Objects and Methods

Cleaning objects: copper and stainless steel pipes.

Method: 1.pre-installation has been pickled before, and now the inner wall of the steel pipe without rust, iron oxide; 2.in the pre-installation of dirty pipe joints; 3.the need to clean the pipe and the joint removed, the pipe with a cloth (to not fall off the lint yarn) dip in kerosene to wipe the pipe clean, both ends and the joint soaked in kerosene cleaning, and then the pipe is coated with machine oil or filled with grease, both ends sealed well to be installed; 4.after cleaning there must not be visually Visible pollutants (such as iron filings, fibrous impurities, welding slag, etc.), pay special attention to the inner wall of the weld slag must be thoroughly cleaned.

Pickling Objects and Methods

Object of cleaning: Steel pipe that has not been pickled before pre-installation; steel pipe that has been pickled but now has serious rust.

Method. 1.Use degreasing agent to remove the grease adhering to the pipeline; 2.Remove the dirt on the pipe with clean water; 3.Remove the rust spots and rolling iron chips on the pipe wall in the pickling solution; 4.Rinse the adhering materials produced in the above operation with clean water, and rinse the inside of the pipe with high-pressure water; 5.Neutralize the residual acid on the pipe with alkali solution; 6.For effective drying the pipe should be immersed in hot water or steam drying 7.Check the pipe after pickling to see if it is clean; 8.Seal the opening of the pipe with plastic or plastic tape immediately after pickling to avoid the intrusion of foreign matter and water.

Screwed on Right: The Pros and Cons of JIC Hydraulic Fittings

By Charles Kolstad, Marketing Manager, Tameson

JIC fittings, also called SAE J514 hydraulic fittings, play an essential role in everyday applications. They are used extensively in agricultural equipment, the construction industry, heavy machinery, automotive industries, and more.

The fittings stem from AN fittings, which were developed by Parker then developed further by the U.S. military around the time of World War II. Developed by the U.S. Army and the U.S. Navy (hence &#;AN&#; in the name) for use in aviation applications, then further developed to high 3A/3B thread-class performance standards and tolerances, the popularity of the fittings quickly took off.

This article explores the origins, uses, and the pros and cons of JIC fittings and compares them to AN fittings.

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In the aftermath of the World War II, many AN flared-fitting designs and specifications hit the market and caused confusion on which standard should be used where. Manufacturers need a specific standard.

The Joint Industry Conference standardized the AN design with a 2A/2B thread class to make manufacturing easier. The fitting became known as the JIC fitting. It delivered high performance at lower cost and a simpler manufacturing process than the AN fitting of the 3A/3B thread class.

The conference wanted the fitting standard to have the same reputation as the standards of the Society for Automotive Engineers International. SAE International represents over 100,000 engineers and experts in the aerospace, automotive, and commercial vehicle industries.

The conference persuaded a committee of SAE engineers to accept the task, and they were instrumental in developing the standard. In , the SAE standard 37° flare fitting was incorporated into SAE J514. ISO , replaced by ISO -2 in , became an ISO standard for the fittings in .

The majority of JIC hydraulic fittings are used in the agriculture, construction, mining, and automotive industries. Despite not meeting the high-performance standards of AN fittings, SAE 37° 2A/2B UN/UNF series threads are designed for optimum thread fit that balances manufacturing capabilities, convenience, economy, and fastener performance.

Differences between JIC and AN fittings

JIC and AN fittings have always been similar in design, function, and size. However, there are considerable differences between them. One of the significant differences is economics. Due to the design factors, AN fittings are considerably more expensive. The price difference comes from being manufactured to tight design tolerances. It is also considered uneconomical to use AN fittings where the application does not demand them. There are also other main differences.

Threads. On AN 37° flare fittings, male and female fittings are produced to class 3A/3B UNJ/UNJF with a radiused root thread. J screw threads are made with a root radius, improving the tensile stress area of the fastener. It also reduces the stress concentration in the thread. Besides offering better fatigue life, it makes the thread considerably stronger, besides offering the benefit of better fatigue life and tighter for military, aerospace, and aircraft applications.

During the production of SAE 37° flare fittings, the male and female threads are made according to class 2A/2B UN/UNF. These fastener classes are designed for optimum thread fit that balances manufacturing capabilities, convenience, economy, and fastener performance.

Military vs. industrial standards. The AN flare fittings conform to the MIL-F- specifications and the SAE aerospace (AS) standard AS. Fittings manufactured under SAE/ISO 37° conform to U.S. Department of Defense MIL-F- and SAE J514/ISO -2 standards.

Materials. Because of where AN fittings are used, they are commonly made out of more metals or composites of costly materials. SAE 37° flared fittings or JIC fittings do not have this requirement and are often made of more standard materials. AN fittings are available in carbon steel, stainless steel (CRES), aluminum, titanium, and copper-nickel. SAE 37° fittings are commonly made out of carbon steel, stainless steel, and brass.

JIC 37° flare fittings design. AN 37° flare and industrial 37° flare fittings function, operate, and look identical. It is not surprising that these fittings are sometimes used interchangeably. The male JIC fitting connects to a 37° female flare fitting or flared tube. The fitting seals through a metal-to-metal seal between the flared tube or the nose of the female and the male fitting. The relatively small seal area makes for a compact design, while JIC fittings benefit from a low-assembly torque, high-temperature and high-pressure capability.

Thread classes

As previously mentioned, JIC fittings according to SAE J514 are designed and fabricated according to the 2A/2B thread fit. Thread fit combines the allowances and tolerances between the male and female threads or how they fit into each other. In essence, it is a measure of tightness or looseness between the two. There are six standard classes for unified inch threads:

• 1A / 2A / 3A: The thread fit class standard for external or male threads.

• 1B / 2B / 3B: The thread fit class standard for internal or female threads. 

All six classes are clearance fits. As the male and female fittings are joined, they assemble without interference. As the number increases, the tolerances between the threads become tighter.

• Classes 1A and 1B are considered to have highly loose tolerances. Assembly and disassembly can be done quickly and easily with this class. It is rare to specify this thread fit other than low-carbon threaded rod and machine screws.

• Classes 2A and 2B offers a balance between fastener performance, production efficiency, and economy. This thread fit is used in almost all commercial and industrial fasteners.

• Classes 3A and 3B should be used when tight tolerances are required. Safety is a critical consideration in the design of these fasteners. These fittings have very tight tolerances and no allowances.

UN or UNJ Threads

In North America, the Unified Thread Standard specifies thread forms and series, allowances, tolerances, and designations for screw threads. It standardizes bolts, nuts, and other threaded fasteners. On unified screw threads, the flank angle is 30°, and the threads are symmetrical. For this reason, they are commonly referred to as 60° threads.

UNC, UNF, and UNEF threads are almost identical to UNJ, UNJC, UNJF, and UNJEF threads. The letter J indicates that these screw threads have a much greater root radius (UNJ, UNJC, UNJF, and UNJEF). As a result, the tensile stress area of the fastener is improved, and the stress concentration factor in the thread is reduced. This leads to a stronger thread. Thread tolerances 3A/3B are standard for UNJ threads. Bolts with a UNJ thread root have a gentler curve that requires a shallower thread root. Since the thread root is so shallow, it cannot mate with a UN nut, so a UNJ nut is also specified.

Pros and cons of JIC fittings

Flared fittings are significantly superior to pipe fittings in terms of design and performance. Flared fittings have long been used instead of pipe fittings for most hydraulic design applications. There are several advantages to using flared JIC or J514 fittings. These include a wide selection of flared fittings in accordance with SAE J514 and availability in a variety of sizes and shapes. Because they were produced to the SAE J514 standard, they can be interchanged with the same product groups produced by different manufacturers, as long as they have been produced to the same standard. Also, they are suited for high-temperature applications because they are not fitted with an O-ring.

There are, however, some disadvantages to using JIC fittings. Specific applications (such as high-vibration applications) have a lower pressure rating than is required. These seals have a metal-on-metal construction, so they are only suitable for hydraulic, liquid, and noncritical applications. The assembly of the 37° flare fittings can cause some nose collapse, which is made worse by over tightening. In turn, this causes a reduction in flow diameter.

Installing JIC fittings

JIC fittings should be installed using the flats-from-wrench-resistance method. This is a relatively simple way to check that the connection is torqued sufficiently without damaging the fit or thread. With the flats method, it is possible to eliminate the effects of plating, lubrication, and surface finishes on torque requirements.

Tighten JIC hose fittings properly with the following steps:

• Connect the female and male connectors and tighten with a wrench (about 30 lb.in. or 3.39 Newton meter) until you feel a slight resistance. This resistance determines the wrench resistance point.

• With a permanent marker, mark this position on both the male and female fittings.

• Using a JIC fittings chart, tighten the nut further according to the number of flats. One flat is equal to 1/6 of a turn on a hexagonal tube nut.

• Once the nut has been tightened to the required number of flats, mark the female and male connections again. It will also serve as a secondary reference point to check the tightness of the connection over time and serve as a reminder to reconnect after maintenance.

Knowledge of which fittings to use in an application helps ensure that the application runs smoothly and can help save money.

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