Technical guide for rubber hoses

Rubber hoses selection

 

Rubber hoses selection

The function of a hose is to convey different solid, liquid or gaseous products either by suction or by discharge.
The large range of tecalemit rcmh flexible hoses responds to many diverse applications as these are designed in a different way according to their use.
For the choice of an industrial hose, the user or prescriber should take a certain number of elements into consideration.

Hose structure :

A hose is comprised of 3 elements :
- the inner tube ensuring tightness is made from homogenous polymer presenting excellent resistance to the conveyed product. iI must have the best possible surface finish.
- the reinforcement gives the hose its physical and mechanical properties : resistance to both positive and negative pressure, resistance to kinking, traction; this reinforcement can combine several technical solutions to adapt to conditions of use : metal or textile braids or plies, metal or plastic spirals, cable plies, electrical conductors.
It also guarantees the dimensional stability of the inner tube thereby contributing to tightness of the hose.
- the outer cover is made from homogenous polymer and intended to isolate the reinforcing structure from the environment.

Nature of conveyed products :

These are extremely varied and have been classified into 7 main families :
- Water (part N°s beginning with 1)
- Air and gasses (part N°s beginning with 2)
- Hydrocarbons (part N°s beginning with 4)
- Steam (part N°s beginning with 5)
- Chemical products (part N°s beginning with 6)
- Abrasive products (part N°s beginning with 7)
- Liquid food products (part N°s beginning with 8
(hoses intended for use with hydraulic oils can be found in the tecalemit flexibles hose catalogue)

Environment :

- Safety of operators
- Protection of the environment
- Ambiant temperature
- Atmospheric conditions
- Possibility of impacts or abrasion
- Presence of corrosive products

State of conveyed product :

Liquid, gaseous, solid or mixture of same

Working method :

By suction, under pressure or by gravity

Working conditions :

Pressure and temperature of fluid, pressure surges, pressure peaks, frequency of use

Characteristics of use :

Flexibility and ease of handling are considered and also :
- Imposed bend radius
- Vibrations of the system
- Applied traction
- Flexions
- Acceptable connections

Standards and regulatory constraints :

These particularly concern the food quality of inner tubes, rules relative to the transport of dangerous products, safety factors between pressure and burst pressures.

Inner diameter of hose (mm) :

The inner hose diameter is without doubt the first citerion of choice.
Choosing too small a diameter provokes important pressure losses and an increase in fluid velocity detrimental to hose service life in the case of abrasive products.
Choosing too large a diameter gives way to a needless increase in weight, size and cost of the installation and a reduction in ease of handling.
This diameter can depend only on the type of end-connection used, variable according to the application. this diameter is often used to designate the hose.

Outer diameter (mm) :

The outer diameter of the hose indicates its outer size. it is also necessary to know it in order to select mounting devices and certain types of fittings.

Working pressure :

Expressed in bars by the abbreviations PS (pression de service - working pressure), PMS (pression maximale de service - maximum working pressure), PMO (pression maximale d’utilisation - maximum service pressure), WP (working pressure), PMA (pression maximale admissible - maximum admissible pressure).
Tecalemit rcmh hoses are designed and manufactured for continuous service at the working pressure indicated on each data sheet.

Test pressure :

Expressed in bars by the abbreviations PE (pression d’épreuve - test pressure) or TP (test pressure) the test pressure is very variable according to requirements of the applicable standards or those of the customer.
gGenerally it is obtained by multiplying the working pressure by a safety factor (1.5 or 2 for example).

Burst pressure :

Expressed in bars by the abbreviations PLNE (pression limite de non-éclatement - pressure limit before bursting) or BP (burst pressure.
The values indicated in TECALEMIT RCMH® data sheets are those of the limit before bursting.
They are guaranteed for hoses before use and having been equipped with end-fittings in the preceeding month.

Working temperatures :

The temperatures specified in tecalemit rcmh data sheets are the maximum admissible temperatures of the hose for the fluid for which the hose is designed. please consult our technical department for the use of the hose with any other fluids.
Hoses may be used in different ambiant temperatures after having been priorly fitted with a heat-resistant sheath, without which the hose outer cover would rapidly age, harden and become brittle.

Bend radius :

Expressed in millimeters, minimum bend radii are indicated by measuring at hose centre line, at maximum working pressure and without hose flexion.
In the case of a hose without internal metal spiral, it defines the radius at which the hose may be rolled with a reduction of 15% of its internal section.

Resistance to traction :

Any traction on a hose must be exerted in the centre line of the end-fittings.
Only metal reinforced hoses can reasonable support any off centre-line tractions.
Tractions on suction hoses with metal spiral (helix) must be avoided.
They reduce working pressure and the internal section of the hose.

Resistance to vacuum :

All our suction hoses have maximum resistance to vacuum.
Kinking or crushing are particularly detrimental to the resistance of hoses to negative pressure.

Length :

It is defined by the working length between connections, the length from fitting joint to fitting joint and the overall length from one end-fitting to the other.

Torsion :

Torsions must absolutely be avoided.
They give way to a rapid deterioration of hoses.

Products or fluids conveyed :

It must be ascertained that the fluid conveyed is compatible with the hose inner tube material, taking into account its concentration and temperature.
Please consult the chemical compatibility chart at the end of this catalogue or contact our technical department.

Electrical conductivity :

Hoses may, or may not, be comprised of conductive mixtures.
Resistances per metre of the inner tube and of the outer cover must be taken into consideration, as well as that between the inner tube and the outer cover.
Moreover, copper braids or small cables may be spirally embedded into the hose wall to ensure electrical conductivity.
For difficult cases and for ease of use, hoses may have the braids overhanging the hose ends by a few centimeters.

External conditions :

Environmental conditions of where the hose is to be used should be taken into account in order to protect it from high temperatures, abrasion, contact with detergents or oils.
The latter generate swelling of the rubber comprising the outer cover, reducing its properties.
Hoses may be used in different ambiant temperatures after having been priorly fitted with a heat-resistant sheath, without which the hose outer cover would rapidly age, harden and become brittle.

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