Technical guide for hydraulic hoses
Preface : reminder on hose structure
A hose has 3 main components :
- An inner tube, for oiltightness, is made from homogenous polymer with excellent resistance to the product conveyed.
- A reinforcement giving the hose its physical and mechanical properties : resistance to pressure, to vacuum, resistance to kinking, tensile strength.
This reinforcement can combine several technical solutions to adapt to conditions of use : textile or metal braiding or spirals, plastic or metal spirals, cable spirals, electrical conductors.
More over, it guarantees the dimensional shape of the inner tube, thereby contributing to tightness of the hose.
- The outer cover is made from homogenous polymer and destined to isolate the reinforcement from the environment.
The user or prescriber should take the following aspects into consideration :
- Safety of operators
- Protection of the environment
- Ambient temperature
- Atmospheric conditions
- Risk of impacts or abrasion
- Presence of corrosive products
State of product conveyed :
Liquid, gaseous, solid or a combination of same
Method of use :
By suction, pressure or assisted
Conditions of use :
Pressure and temperature of fluid, pressure surges, pressure peaks, frequency of use
Characteristics of installation :
- Imposed bend radius
- Acceptable fittings
The rest of this guide deals more with hydraulic hose up to inner diameter 2” (50,8mm) for oleo-hydraulic power applications and transport of gaseous fluids under high pressure.
Expressed in millimetres and fractions of an inch as well as in modules (dash-sizes). These are equal to 1/16 of an inch for all our hoses except for hose type SAE100 R5 (our hose types T510 and T511).
The inner diameter of a hose is without doubt the first criterion to choose.
Choosing a diameter too small would have for effect :
- Heating of the installation via the joule effect due to overspeeding of the hydraulic fluid flow
- Important pressure drops
- Loss of efficiency and premature wear of hydraulic pumps (suction)
Choosing a diameter too large would unnecessarily increase weight, size and cost of the installation.
Choosing the right inner diameter of hose is therefore primordial.
This table is destined to help you determine hose inner diameter. It gives pressure drops for standard oil.
|Inner diameter (mm)|
|Laminary flow||Transitory flow||Turbulent flow|
|Table of pressure drop in millibars (mb) per metre of rubber hose without end-fittings by inner diameter in millimetres and by flow rate in litres per minute (l/m) for a standard hydraulic oil of 31,8 centistokes (mm2/s) and with a density of 878 kg/m3.|
The following abacus corresponds the flow rate (in litres per minute), the inner diameter (in millimeters) and the speed (in meters per second) of a fluid within a hose.
It is just necessary to trace a straight line through two known values to obtain the third.
In the example shown by a dotted line, for a flow Q of 6 l/m, to have a speed V of 1 m/s, it is necessary to have an inner diameter d of roughly 12mm.
Part of the energy necessary for the transfer of fluid in the hose is lost through friction : it is called pressure drop.
This is proportional to the speed of the fluid at low speeds.
At higher speeds it becomes proportional to the square root of the speed and therefore excessive.
The limit between these two possibilities is identifiable by the Reynolds number which must be inferior to 2300 for the flow to be satisfactory.
Reynolds number = Re = V.D/nu <2300
V = speed of fluid in millimeters per second
D = inner diameter of hose in millimeters
nu = kinematic viscosity in centistokes
when the Reynolds number is lower than 2300, it is said to be laminary, when it is between 2300 and 3000 it is called transitory and for values above, it is said to be turbulent.
Expressed in bar with the abbreviation WP.
Tecalemit flexibles hoses are designed and produced to work continuously at the working pressures indicated on each data sheet and repeated in the table by diameter and type.
As an idincation, it is considered that using a hose at 20% higher pressure than recommended reduces life span by half.
|Working pressure (in bars)|
Expressed in bar with the abbreviationTP.
Test pressure is generally twice the working pressure, it should be maintained for over 30 seconds without exceeding 15 minutes .
Hydraulic circuits generally present pressure surges and/or temporary overpressures whose values exceed the nominal admissible pressures for the majority of the circuits components.
In this case, it is necessary to increase the safety factor, which is usually 4, between the working pressure and the theoretical burst pressure.
Tthis safety factor can be reduced to 3.15 if no pressure surges are present.
Expressed in bar with the abbreviation of BP.
The values indicated on Tecalemit Flexibles® data sheets are before bursting.
They are guaranteed for hoses having never been in use and equipped with fittings in the preceeding month.
The temperatures specified in Tecalemit Flexibles® data sheets are the maximum admissible working temperatures for the hose with standard hydraulic oil.
It can be considered that 10°C higher in temperature can halve the life span.
For other fluids, please contact our technical department, as the maximum admissible temperature could be higher or lower than indicated.
iIt is strongly advised not to use hoses at maximum pressures and temperatures at the same time.
Hose assemblies can be used in different ambient temperatures after having been protected by an adequate heat-resistant sheath, without which the outer cover would be subjected to premature aging, harden and become brittle.
Expressed in millimeters, bend radii are indicated by measuring from the centreline of the hose, at maximum working pressure and without flexing of the hose.
Should there be flexing of the hose, minimum bend radius should be increased by the multiplication factor N in the table below.
A lower bend radius can be acceptable, provided the working pressure is lowered.
Any pulling forces must be made in the centreline of end-fittings.
Only hoses with metal reinforcement can sufficiently resist off-centreline pulling forces.
Pulling forces should be avoided on suction hoses incorporating a wire spiral as well as hoses intended to transmit power via hydraulic oil.
They would have for effect to reduce admissible working pressure and the internal dimension of the hose.
All our suction hoses have maximum vacuum resistance.
Also, our data sheets indicate maximum admissible vacuum values for high pressure hoses with metal reinforcement, as well as the SAE 100 R3 hose with textile reinforcement.
Accidental kinking or flattening are particularly detrimental to vacuum resistance of hoses.
Tecalemit Flexibles® hoses are manufactured to withstand vibrations.
In order to optimise their life span, it is recommended to avoid them in as much as possible, as vibrations (and flexions) are the main sources of wear and heating, particularly at end-fittings.
Twisting must be avoided. They give way to a rapid deterioration of hoses.Chemical resistance:
Compatibility of the hose inner tube with the fluid conveyed must be ascertained.
In the same respect, the outer cover and its environment should be taken into consideration.
The table of chemical resistance found in this catalogue gives the main information, but please contact our technical department in case of doubt.
Hoses must be adapted to conveying gaseous fluids when necessary.
The hose outer cover must be micro-perforated, in order to eliminate any gas build-up in the hose reinforcement structure.
Other precautions should be taken in assembling and installing the hose. these are detailed in the technical handbook.
Metal spiral hose cannot convey gaseous fluids (microperforation is not possible).
In general, it can be said that metal-reinforced hoses are conductive and that textile-reinforced hoses are not.
Resistance per metre of hose inner tube and outer cover should be taken into consideration, and also that between the inner tube and the cover.
For special application, please consult the technical department.
Tecalemit Flexibles® high pressure hose is manufactured with a braid angle which geometrically cancels any dimensional modifications due to pressure, that is : stretching with reduction of diameter or, alternatively, retraction accompanied by an increase in diameter.
Even so, it strongly advised to check measurements during pressure tests.