Safety Guide For Hose Assemblies
- HMK
- Safety Guide For Hose Assemblies
Hydraulic hose and hose assemblies have a limited life dependent on service conditions to which is applied.subjecting hose and hose assemblies to conditions more mevere than the recommended limits significantly reduce service life.Exposure to combination of recommended limits(i. e.,continuous use at maximum 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 premature failures.bodily injury.and damage to property.
1. The following is a list of factors which must be considered before the selection of a hosecan be made:
1.1 Line size
In order to achieve maximum efficiency in a hydraulic system.it is necessary to keep pressure losses(resistance to the volumetric flow)to a minimum when a fluid is conveyed by the different types of flow lines.
When a fluid flows through a flow line.heat is fenerated by friction.Thus part of the energy is lost as heat energy,which results in a pressure loss.
These pressure lossed depend upon
Flow velocity(for a given volumetric flow.the fluid flow velocity increases with a decrease in the cross sectional area of a flow line and vice vers
a) length of the flow line.
b) the viscosity of the fluid flowing
c)the density of the fluid flowing
d) the type of flow
1.2 Pressure
After determining the system pressure for an hydraulic system.hose selection must be made so that the recommended maximum operating pressure specified by a given hose,is epual or greater than the system pressure.Dynamic pressure is common for all hydraulic systems.
Pressure surges which exceed the maximum working pressure(pressure relief valve setting)affect the service life of system components,including a hose assembly and therefore need to be taken into consideration.Hoses used for suction lines must be selected to ensure the hose will withstand the negative pressure of the system.
1.3 Temperature
Care must be taken to ensure that the operating temperature of the fluid being conveyed anf ambinent temperatures.do not exceed the limitations of the hose.Special care must be taken when routing near hot manifolds or molten metal.
1.4 Fluid Compatibility
Hose selection must assure compatibility of the hose tube,cover,reinforcement,and fittings with the fluid used.Addtional caution must be observed in hose selection for gaseous applincations.Some fire resistant fluids require the same hose as petroleum oil.Some use a special hose.while a few fluids will not work with any hose at all.
1.5 Permeation
Permeation(that is,seepage through the hose)will occur from inside the hose to outside when hose is used with gases.liquid and gas fuels.and refrgerants(including but not limited to such materials such as helium.fuel oil,natural gas or freon).This permeation may result in high concentrations of vapours which are potentially flammable.explosive,or toxic,and in loss of fluid.
Even thougt the fluid compatibility acceptable,you must take into account the fact that permeation will occur and could be hazardous.
Permeation of moisture from outside the hose to inside the hose will also occur. If this moisture permeation would have detrimental effects(particularly but not limited to refrigeration and air conditioningsystems),incorporation of sufficient drying capacity in the system or other appropriate system safeguards should be selected and used
1.6 Routing
Attention must be given to optimum routing to minimize inherent problems.Restrain,protect or guide hose with the use of clamps if necessary to minimize risk or damage due to excessive flexing.whipping or contract with other moving parts or corrosives.Determine hose lengths and configurations that will result in proper routing and protection from abrasion,snagging or kinking anf provide leak resistant connections.
1.7 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 including but not limited to ultraviolet light,heat,ozone.moisture,water,salt water,chemicals,and air pollutants can cause degradation and premature failure and,therefore,must be considered.
1.8 Mechanical Loads
Extemal forces can significantly reduce hose life.Mehanical loads which must be considered include excessive flexing,twist,kinking,tensile or side loads.bend radius,and vibration.Use of seivel 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.
1.9 Abrasion
While a hose is designed with a reasonable level of abrasion resistance,care must be taken to protech 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.
1.10 Proper End Fitting
Care must be taken to ensure proper compatibility exists between the hose and coupling selected based on the manufactureris recommendations substantiated by testing to industry standards.
1.11 Length
When establishing proper hose length,motion absorption,hose length changes due to pressure,as well as hose and machine tolerances must be considered.
1.12 Specifications and Standards
When selecting hose and fittings,government,industry,and manufactuer’s specifications and recommenddtions must be reviewed as applicable .
1.13 Hose Cleanliness
Hose aomponents may vary in cleanliness levels. Care must be taken to ensure that the assemblies selected have an adequate level of cleanliness for the application.
1.14 Welding and Brazing
Heating of plated parts,including hose fittings and adaptors,above 232°C such as during welding,brazing,or solde-ring may emit deadly gases.
1.15 Electrical Conductivity
Certain applications require that a hose be non-conductive to prevent electrical flow. Other applications require the hose to be sufficiently conductive to drain off static electricity.
For application that require hose to be electrically non-conductive, including but not limited to applications near high voltage electric lines,only special non—conductive hose can be used.
The electrical conductivity or non-conductivity of hose and fittings is dependant upon many factors and may be susceptible to change. These factors include but are not limited to the varions materials used to make the hose and the fittings, manufanturing methods(including moisture control),how the fittings contact the hose, age and amount of deterioration of damage or others changes, moisture content of the hose at and particular time, and others factors.
Installation—After the selection of the correct hose,the following factors must be considered prior to hose and fittings assembly and installation.
2.1 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,The hose must be examined for cleanliness, obstructions,blisters,cover loosenessm,or other visible defects.
2.2 Hose and Fitting Assembly
Do not assemble a fitting on a hose that is not specifed for that hose.
2.3 Related Accessories
Crimp or swage hose or fittings only with approved awage or crimp machines.
2.4 Reusable / Permanent
Do not reuse any reusable hose coupling that has bloen or pulled off a hose. Do not reuse an permanent (that is , crimped or swaged)hose fitting or any part thereof.
2.5 Minimum Bend Radius
Installation of a hose at less than the minimum listed bend radius may significantly reduce the hose life. Particular attention must be given to avoid sharp bending at the hose / fitting juncture.
2.6 Twist Angle and orientation
Hose installations must be such that relative motion of machine components does not produce twisting.
2.7 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 contant with other mechanical components. Care must be taken to ensure such restraits do not introduce additional stress or wear points.
2.8 Proper Connection of Ports
Proper physical installation of the hose requires a correctly installed port connention while ensuring that no twist or torque is transferred to the or damage to sealing surfaces are corrected or eliminated.
2.9 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.
2.10 System Checkout
After completing the installation entrapment must be eliminated and the system pressurized to the maximum system pressure and checked for proper function without any leaks.Personnel must stay out of potential hazardous areas while testing.
3. Hose And Fitting Maintenance Instructions
Even with proper selection and installation. hose life may be significantly reduced without a continuing maintenance program. Frequency should be determined by the severity of the application and risk potential. A maintenance program must be established and followed to include the following as a minimum.
3.1 Visual Inspection Hose / Fitting
Any of the following conditions require immediate shut down and replacement of the hose assembly.
a) Fitting slippage on hose.
b) Damaged, cut or abraded cover(any reinforcement exposed)
c) Hard, stiff,heat cracked, or charred hose.
d) Cracked, damaged, or bably corroded fittings.
e) Leaks at fitting or in hose.
f) Kinked, crushed, flattened or twisted hose.
g) Blistered, soft, degraded, or loose cover.
3.2 Visual Inspection All Other
The following items must be tightened, repaired or replaced as required。
a) Leaking port conditions.
b) Remove excess dirt build-up.
c) Ciamp, guards, shields.
d) System fluid level, fluid type and air entrapment.
3.3 Functional Test
Operate the system at maximum operating pressure and check for possible malfunctions and Freedom from leaks. Personnel must stay out of potential hazardous areas while testing.
3.4 Replacement Intervals
Specific replacement intervals must be considered based on previous service life, government or industry recommendations. or when failures could resulys in unacceptable downtime, damage, or injury risk.
