Flexible Hose - Modes of Movement & Motion

Flexible Hose - Modes of Movement & Motion

FLEXIBLE HOSES ARE USED FOR THE FOLLOWING MODES OF MOVEMENT.

1. STATIC INSTALLATIONS : Where the flexible hose is used to connect pipe work out of alignment and remain in static position.

2. OCCASIONAL FLEXING : When the hose is only required to flex occasionally ,such as manual handling.

3. COSTANT FLEXING : When the hose is required to flex continuously,usually on moveing machinery.

4. VIBRATION : High frequency,low amplitude movement,i.e. on a compressor.

PRESSURE – FOURE EFFECTS

SYSTEM PRESSURE: 

System pressure is the first factor considered in selecting a hose or wall thickness. Where significant pressure fluctuations are not present,a standard hose may be selected by choosing one rated at a pressure equal to or greater than your nominal operating pressure.

PULSATING PRESSURE:

Pulsating pressure is a continuous rippling pressure superimposed on the operating pressure.If the pulsations are significant it is proper to provide margin in selecting the rated pressure for a standard hose.

SURGE PRESSURE:

Surge pressure usually occurs during system start up,shut down and rapid valve closure.It is proper to consider the possibility of surge pressure and to provide adequate margin.

FLEXIBILITY :

Logically, increasing pressure requires a heavier wall and braid tightens the braid grip increasing hose stiffness proportionately. As covered in the vibration section the tightening of the braid is valuable in controlling vulnerability by providing necessary damping.

HOSE MOTION – THREE TYPES

ANGULAR MOTION:

Occurs when one end of the hose is held fixed and the other is deflected in an arc.

OFFSET MOTION:

Occurs when one end of the hose is fixed and the other end is offset but remains parallel to the fixed end. Do not allow this motion to stretch the hose.Use a stress relief loop or equivalent to provide slack.

AXIAL MOTION:

Occurs when one end of the hose is held and the other end of the hose is deflected along the axia of the hose.This type of motion should only be applied to unbraided annular hose or to braided hose where a stress relief loop or offset is provided so that the motion is only locally axial and the hose is not stretched or compressed.