Hydraulics - Selection & Inspection


Selection Installation & Maintenance Of Hose And Hose Assemblies

SAE J1273 NOV ‘91. SAE RECOMMENDED PRACTICE

Report of the Fluid Conductors and Connectors Technical Committee, approved September 1979 and reaffirmed May 1986. Completely revised by the SAE Fluid Conductors and Connectors Technical Committee SC2 - Hydraulic Hose and Hose Fittings November 1991. Rationale statement available.
Technical guidance on the selection of hydraulic hose & fittings

Scope

Hose (also includes hose assemblies) has a finite life and there are a number of factors which will reduce its life. This SAE recommended practise is intended as a guide to assist system designers and/or users in the selection, installation and maintenance of hose. The designers and users must make a systematic review of each application and then select, install and maintain the hose to fulfil the requirements of the application. The following are general guidelines and are not necessarily a
complete list.

WARNING - IMPROPER SELECTION, INSTALLATION OR MAINTENANCE MAY RESULT IN PREMATURE FAILURES, BODILY INJURY OR PROPERTY DAMAGE.

Reference

The following publications form a part of this specification to the extent specified herein. The latest issue of SAE publications shall apply.

  • 2.1.1 SAE Publications - Available From SAE, 400
    Commonwealth Drive, Warrendale, PA 15096-0001.
    J516 - Hydraulic Hose Fittings
    J517 - Hydraulic Hose

Selection

The following is a list of factors which must be considered before final hose selection can be made:

Pressure
After determining the system pressure, hose selection must be made so that the recommended maximum operating pressure is equal to or greater than the system pressure. Surge pressures higher than the maximum operating pressure will shorten hose life and must be taken into account by the hydraulic designer.

Suction
Hoses used for suction applications must be selected to ensure the hose will withstand the negative pressure of the system.

Temperature
Care must be taken to ensure that fluid and ambient temperatures, both static and transient, do not exceed the limitations of the hose. Special care must be taken when routing near hot manifolds.

Fluid Compatibility
Hose selection must assure compatibility of the hose tube, cover and fittings with the fluid used. Additional caution must be observed in hose selection for gaseous applications.

Size
Transmission of power by means of pressurised fluid varies with pressure and rate of flow. The size of the components must be adequate to keep pressure losses to a minimum and avoid damage to the hose due to heat generation or excessive turbulence.

Routing
Attention must be given to optimum routing to minimise inherent problems.

Environment
Care must be taken to ensure that the hose and fittings are either compatible with or protected from the environment to which they are exposed. Environmental conditions such as ultraviolet light, ozone, salt water, chemicals and air pollutants can cause degradation and premature failure and, therefore, must be considered.

Mechanical Loads
External forces can significantly reduce hose life. Mechanical loads which must be considered include excessive flexing, twist, kinking, tensile or side loads, bend radius and vibration. Use of swivel type fittings or adaptors may be required to ensure no twist is put into the hose. Unusual applications may require special testing prior to hose selection.

Abrasion
While a hose is designed with a reasonable level of abrasion resistance, care must be taken to protect the hose from excessive abrasion which can result in erosion, snagging and cutting of the hose cover. Exposure of the reinforcement will significantly accelerate hose failure.

Proper End Fitting
Care must be taken to ensure proper compatability exists between the hose and coupling selected based on the manufacturer’s recommendations substantiated by testing to industry standards such as SAE J517. End fitting components from one manufacturer are usually not compatible with end fitting components supplied by another manu- facturer (i.e., using a hose fitting nipple from one manufacturer with a hose socket from another manufacturer). It is the responsibility of the fabricator to consult the manufacturer ’s written instruction or the manufacturer directly for proper end fitting componentry.

Length
When establishing proper hose length, motion absorbtion, hose length changes due to pressure, as well as hose and machine tolerances must be considered.

Specifications and Standards
When selecting a hose, government, industry and manufacturers’ specifications and recommendations must be reviewed as applicable.

Hose Cleanliness
Hose components vary in cleanliness levels. Care must be taken to ensure that the assemblies selected have an adequate level of cleanliness for the application.

Electrical Conductivity
Certain applications require that the hose be non- conductive to prevent electrical current flow. Other applications require the hose to be sufficiently conductive to drain off static electricity. Hose and fittings must be chosen with these needs in mind.

Installation

After the selection of proper hose, the following factors must be considered by the installer:

Pre-Installation Inspection
Prior to installation, a careful examination of the hose must be performed. All components must be checked for correct style, size and length. In addition, the hose must be examined for cleanliness, I.D. obstructions, blisters, loose cover or any other visible defects.

Follow Manufacturers’ Assembly Instructions
Hose assemblies may be fabricated by the manufacturer, an agent for or customer of the manufacturer or by the user. Fabrication of permanently attached fittings to hydraulic hose requires specialised assembly equipment. Field-attachable fittings (screw style and segment clamp style) can usually be assembled without specialised equipment although many manufacturers provide equipment to assist in this operation. SAE J517 hose from one manufacturer is usually not compatible with SAE J516 fittings supplied by another manufacturer. It is the responsibility of the fabricator to consult the manufacturer’s written assembly instructions or the manufacturer directly before intermixing hose and fittings from two manufacturers. Similarly, assembly equipment from one manufacturer is usually not interchangeable with that of another manufacturer. It is the responsibility of the fabricator to consult the manufacturer ’s written instructions or the manufacturer directly for proper assembly equipment. Always follow the manufacturer ’s instructions for proper preparation and fabrication of hose assemblies.

Minimum Bend Radius
Installation at less than minimum bend radius may significantly reduce hose life. Particular attention must be given to preclude sharp bending at the hose/fitting juncture.

Twist Angle and Orientation
Hose installations must be such that relative motion of machine components produces bending of the hose rather than twisting.

Securement
In many applications, it may be necessary to restrain, protect or guide the hose to protect it from damage by unnecessary flexing, pressure surges and contact with other mechanical components. Care must be taken to ensure such restraints do not introduce additional stress or wear points.

Proper Connection to Ports
Proper physical installation of the hose requires correctly installed port connection while ensuring that no twist or torque is put into the hose.

Avoid External Damage
Proper installation is not complete without ensuring that tensile loads, side loads, kinking, flattening, potential abrasion, thread damage or damage to sealing surfaces are corrected or eliminated.

System Check Out
After completing the installation, all air entrapment must be eliminated and the system pressurised to the maximum system pressure and checked for proper function and freedom from leaks. Note: Avoid potential hazardous areas while testing.

Maintenance

Even with proper selection and installation, hose life may be sig- nificantly reduced without a continuing maintenance programme. Frequency should be determined by the severity of the application and risk potential. A maintenance programme should include the following as a minimum:

Hose Storage
Hose products in storage can be affected adversely by temperature, humidity, ozone, sunlight, oils, solvents, corrosive liquids and fumes, insects, rodents and radioactive materials. Storage areas should always be relatively cool and dark and free of dust, dirt, dampness and mildew.

Visual Inspections
Any of the following conditions requires replacement of the hose:
  • Leaks at fitting or in hose. (leaking fluid is a fire hazard)
  • Damaged, cut or abraded cover. (Any reinforcement exposed.
  • Kinked, crushed flattened or twisted hose.
  • Hard, stiff, heat cracked or charred hose.
  • Blistered, soft, degraded or loose cover.
  • Cracked, damaged or badly corroded fittings.
  • Fitting slippage on hose.
Visual Inspections

The following items must be tightened, repaired or replaced as required:

  • Leaking port conditions.
  • Clamps, guards, shields.
  • Remove excessive dirt buildup.
  • System fluid level, fluid type and any air entrapment.

Functional Test

Operate the system at maximum operating pressure and check for possible malfunction and freedom from leaks. Note: Avoid potential hazardous areas while testing.

Replacement Intervals

Specific replacement intervals must be considered based on previous service life, government or industry recommendations or when failure could result in unacceptable downtime, damage or injury risk.

Hose Service Life

Hydraulic hose (and hose assemblies) has a limited life dependent on service conditions to which it is applied. Subjecting hose (and hose assemblies) to conditions more severe than the recommended limits significantly reduces service life. Exposure to combinations of recommended limits (i.e., continuous use at maximum rated working pressure, maximum recommended operating temperature and minimum bend radius) will also reduce service life. Failure to follow proper selection, installation and maintenance procedures may result in injury to personnel and/or damage to equipment. Hose assemblies in service should be regularly inspected for leaks, abrasion, kinks, cover blisters or other such damages. Assemblies showing signs of wear or damage should be replaced immediately. Maximum service life can be obtained by complying with the following recommendations:

  • Working pressure: The hydraulic system pressure should not exceed the rated working pressure of the hose. Pressure surges or peaks exceeding the rated working pressure are destructive and must be taken into account when selecting a hose.
  • Minimum Burst Pressure: Burst pressures are reference pressures intended for destructive testing purposes and design safety factors only.
  • Temperature Range*: Do not expose hose to internal or external temperatures exceeding the recommended limits. Consult additional technical data when hydraulic fluids contain emulsions or solutions. The fluid manufacturer’s recommended maximum operating temperature for any given fluid must not be exceeded, regardless of hose temperature range.
    • *Actual service life at temperatures approaching the recommended limit will depend on the particular application and the fluid being used in the hose. Intermittent (up to 10% of operating time) refers to momentary temperature surges. Detrimental effects increase with increased exposure to elevated temperatures.
  • Fluid Compatibility: The hydraulic assembly (tube, cover, reinforcement and couplings) must be fluid compatible. The correct hose must be used because phosphateester and petroleum base hydraulic fluids have drastically different chemical charateristics. Many hoses are compatible with one or the other but not all fluids.
  • Minimum Bend Radius: Do not bend or flex hose to a radius smaller than the minimum recommended and do not subject hose to tension or torque. This can place excessive stress on the reinforcement and severely reduce the ability of the hose to withstand pressure.
  • Hose Size: The hose size (inside diameter) must be capable of handling the required flow volume. Too small an I.D. for a given volume of flow results in excessive fluid turbulence, pressure drop, heat generation and tube damage.
  • Hose Routing: Restrain, protect or guide hose (clamps can be used) to minimize risk of damage due to excessive flexing, whipping or contacting other moving parts or corrosives. Determine hose lengths and configurations that will result in proper routing and protection from abrasion, snagging or kinking and provide leakresistant connections.
  • Hose Length: Correct hose length determinations include considerations for length changes under pressure, machine vibration and motion, and hose assembly routing.
  • Hose Applications: Select the proper hose for the application. Vacuum service and special fluid or high temperature capabilities are among the applications requiring particular consideration and a specific hose. Do not use hydraulic hose in place of permanent piping
Hose Shelf Life

Storage environment, along with rubber materials can vary the shelf life limit. Some hose materials last longer in storage due to inherent resistance characteristics. Other materials require additives during compounding. These additives are eventually consumed, even in seemingly ideal storage conditions

Shelf life is difficult to quantify as many variables affect the hose. Proper storage precautions can result in three to five years shelf life. Beyond this time there can be significant service life decrease, depending on storage environment variables. Some of these variables are temperature, humidity, ozone, oil, solvents, corrosive materials, fumes, insects, rodents, radioactivity, space allowance and bends.

Hose should be stored in a cool dry area never exceeding +38º (+100ºF). If stored below freezing, pre-warming may be required prior to handling, testing and placing into service. Store hose in original container. Never stack hose too high, as it’s weight can crush hose at the bottom of the stack. Direct sunlight, rain, heaters or being near electrical equipment will reduce hose life.

It is recommended that hose in extended storage be visually inspected and tested prior to use. Hose judged marginal should be replaced to avoid potential failure, property damage or bodily injury. Store hose on a first in-first out basis. Unusually long storage or poor storage environment can deteriorate hose, reduce performance and may lead to premature failure.

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