Choice of hose assembly

 1. correct choice of hose assemblies

Hydraulic hose assemblies are used to transmit forces by means of oil pressure, and consist of flexible hydraulic hoses to which fittings are attached at either end to ensure safe, interlocking connections.

The correct choice of a hose assembly is influenced by many factors, particulary dynamic working pressure, resistance to media handled, operating temperature - both of the medium and of the surroundings.

Follow the instructions...

However, legal and other regulations must also receive careful consideration where hydraulic hose assemblies are used, and the manufacturer should be informed about them when you make your inquiry.

In many cases, observing the instructions for installation will determine the service life of a hydraulic hose assembly.

2. determination of hose dimensions

The necessary inside diameter of a hose assembly is determined by the projected working pressure and the proposed rate of flow.

Never underdimension hoses...

Underdimensioning hose assemblies results in a high rate of flow of the medium. This ensuing turbulence causes in considerable loss of pressure, noise and increased temperatures. This can be detrimental to the entire system.

If underdimensioned valves necessitate smaller hose inside diameters, we recommend the use of suitable adapters which then cause only local constrictions in the system.

 3. dynamic working pressure decisive

In practice hydraulic hose assemblies are subjected to dynamic loading. A hose assembly must therefore be designed for operation at the maximum permissible working pressure specified for the respective hose type and size.

Safety factor 4 : 1

The working pressure of a hydraulic hose assembly is normally a quarter of the theoretical or specified bursting pressure. This safety factor of 4:1 conforms to SAE, DIN and EN-regulations.

Dynamic operating pressures...

is the most frequently operating condition in hydraulic systems. Pure static load is the absolute exception and therefore the "Static Working Pressure" has been eliminated from the standards.

Consider peak pressures...

a hose with a higher pressure rating than the actual working pressure of the installation should be selected for systems in which sudden peak pressures occur. 

 4. Bursting pressure must never be reached

The values specified for bursting pressure are minimum values. They apply only to unused hose assemblies.

The bursting pressure of a hose or a hose assembly must therefore remain a purely theoretical value for the user. In view of the safety requirements imposed on any installation, this value must never be reached - or even approached - in practice.

It is incorrect to assume that comparable hoses of different manufactures have longer service life under the same operating conditions the higher the rating for bursting pressure is. Designers should therefore take dynamic pressure values into consideration!

5. Monitoring high pressure gas systems

High pressure gas systems are dangerous and require regular inspection.

Hose assemblies used in gas systems have to be suitably protected against mechanical damage and chemical end environmental influences.

The hoses of such installations should also be connected in such a way that they cannot whip in the event of a defect occuring.

Perforated outside cover...

The outside cover of a hose assembly used for the conveyance of gaseous media must be perforated.

6. test pressure as safety check

Hose assemblies are statically tested by the manufacturer at suitable test pressures; neither leaks nor failure must occur.

7. temperature affects service life

The operating temperatures given for hoses are the maximum temperatures of the medium. Ambient temperatures must also be taken into consideration (see below).

Continuous operation at high temperatures can affect the service life of the hose and the reliable seating of the fittings.

Temperature resistance depends on medium

Hose assemblies cannot therefore be used for any medium over the specified temperature range. In case of doubt please ask us.

Hoses assemblies will have a considerably longer service life if they are not continually used at the limits of their working pressure, bend radius and temperature of medium and environment.

8. Allow for changes in Length

Every hose is subject to certain changes in length under working pressure.

The standards specify that these values can vary between -4 % and +2 % at maximum working pressure.

This change in length must be taken into consideration in each case when calculating the nominal length of a hose assembly with fittings.

9. check chemical resistance

The chemical resistance of the rubber lining is an important factor to consider when selecting a hose assembly. This should be viewed as a function of the concentration and nature of the duration of exposure to the medium.

In principle the rubber lining is resistant to hydraulic liquids on mineral- or synthetic oil basis, to glycol water mixtures and oil water emulsion but not resistant to phosphate ester based liquids (HFD).

10. observe minimum bend radius

The specified minimum bend radius apply to stationary hose assemblies at maximum working pressure.

The service life of a hose assembly is impaired if bends of less than the recommended minimum bend radius are used. Working pressure should be reduced in such cases.





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