Hose and Fittings Terminology – The basics !
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Selecting the right hose and fittings combination usually belongs to the last steps in the
design of a hydraulic system and its importance is often overlooked and underestimated.
The right hose and fitting combination is however, vital for the overall functionality and
long term service life of the complete system.
This technical handbook and catalogue will provide a guide to correct hose and fitting
selection, as well as highlighting the important safety aspects to their usage as hose
assemblies in the field
Hose
Typically a rubber hose is constructed of an extruded inside synthetic rubber tube that has the sole purpose to keep the conveyed fluid in the hose.
The elastomeric nature of rubber requires that a
reinforcement layer be wound or braided around the tube in order to hold the internal pressure.
The reinforcement layer(s) are either textile or steel (or both).
To protect these inner layers of the hose from the
ambient conditions, an outer synthetic rubber cover is extruded around the reinforcement
Hose Assemblies
Hose Assemblies Installation
The combination of a hose and hose fitting(s) to make a hose assembly, is a critical process that needs
to be carried out by professionally trained personnel who follow strict assembly instructions. Improperly assembled hose fittings can separate from the hose and may cause serious injury or
property damage from whipping hose, or from fire or explosion of vapor expelled from the hose.
(See „Safe Hose Assemblies in 8 Steps“, Page Aa-8)
The hose assembly must be operated within specific limits to maximise a safe and long term service
life. These limits are defined in this catalogue and also by both governmental standards and institutional organisation’s and specifications such as the ISO 17165-2, SAE J1273 or EN982.
Working Pressure
Hose and fitting selection must be made so that the published maximum recommended working pressure of the Hose and fitting are equal to, or greater than the maximum system pressure. Surge pressures or peak transient pressures in the system must be below the maximum working pressure of the hose assembly. Surge pressures and peak pressures can usually only be determined by sensitive
electrical instrumentation that measures and indicates pressures at mili-second intervals. Mechanical pressure gauges indicate only average pressures and cannot be used to determine surge pressures or peak transient pressures.
Proof Pressure Test
This test is typically carried out on customer request according to a method defined by the ISO 1402
standard. The test should be made at normal ambient temperature with a proof test bench using water
or another suitable liquid. The hose assembly should be pressurised for between 30 to 60 seconds at
twice the working pressure of the hose assembly. There should be no leakage or pressure drop.
A complete test report should be provided together with the hose assembly to the customer.
Burst Pressure
All hoses in this catalogue have a pressure design factor of 4:1, implying therefore that the burst pressure (hose destruction) is minimum 4 times the published working pressure. Published burst pressure ratings for hose are for manufacturing test purposes only – burst pressure should never play a role in the selection of a hose.
Fluid Compatibility
The hose assembly (hose inner tube, hose outer cover and hose fittings) must be chemically compatible to both the fluid being conveyed by the hose as well as the medium surrounding it. (the chemical resistance table contained in the catalogue, indicates only the resistance of the hose innertube to the respective fluid)
Temperature Range
In order not to negatively effect the properties of the rubber hoses it should be made certain that fluid and ambient temperatures, both steady and transient, do not exceed the limitations of the hose as published in the catalogue. Temperatures below and above the recommended limit will degrade the hose and failure may occur and release fluid. The mechanical properties of the hose are also influenced by low or high temperatures and should be considered when designing the system.
Hose Size
The power transmitted by means of a pressurised fluid varies with pressure and rate of flow.
The size of the components must be adequate to keep pressure drops to a minimum and avoid aging due to heat generation or excessive fluid velocity. Parker uses the internationally recognised hose dash size as a measurement of the size of their hoses.
This size is a measurement of the inside tube of the hose – not the wall outer diameter.
Hose Bending Radius
The minimum bend radius of a hose refers to the minimum radius that the hose may be bent through whilst operating at the maximum allowable published working pressure. Bending radius is not a measurement or indicator of hose flexibility. The catalogue specified values of bending radii are based on international or Parker specifications and have been proven through rigorous impulse testing of the hose assemblies.
Bending the hose below the minimum bending radius leads to loss of mechanical strength and hence possible hose failure. A minimum straight length of 1,5 times the hose’s outside diameter (D) shall be allowed between the hose fitting and the
point at which the bend starts.
Please click the below Link to download the complete catalogue of Parker Hoses and Fittings.
Parker Hose and Fittings Catalog
Arvi Hitech
http://www.arvihitech.com/
