River Bend Hose Metal Hose Assemblies

The use of braided metal connectors for applications such as pumps, compressors and other mechanical equipment will enhance the overall operation of a system. The optimum design provides a variety of advantages:

Greater flexure without fatigue
Longer service life
Greater capacity for pressure
Increased temperature capacity of media
Absorption of pump vibration and noise
Acceptance of thermal expansion
Reduction in pipe stress due to minor misalignment and pressure variations
Reduction of stress on pumps and compressor housings, reducing long term operation and maintenance costs.

Construction
Corrugated Metal Hose Assemblies are usually made of stainless steel, bronze or other metals depending upon the environment in which it is being used. The corrugated hose is manufactured by forming a rolled strip into a cylindrical thin walled tube. The seams are joined by butt-welding and profile is impressed into the tube.

Annular
An annular configuration is one in which the convolutions on a hose consist of a series of complete circles located at right angles to the longitudinal axis of the hose. This is sometimes referred to as a bellows. An annular hose is better suited for pump connections because it can better sustain torsional stress due to longitudinal expansion from rises in pressure.

Helical
Helical hose is formed from a continuous spiral corrugation into tubing. This design allows for flexibility of the hose assembly under pressure and also possesses unique self-draining properties.

Braid
Metal wire braid on a hose assembly restrains against hose elongation under higher pressures and acts to dampen vibration. A second layer of braid may be used to increase pressure ratings. A heavy braid will also increase abrasion resistance. Optimal braid coverage will contain the core under pressure and reduce the possibility of squirm. Properly designed braid coverage will balance pressure capability with flexing requirements as well as minimize braid wear on the crown of the corrugation.

Hose Assembly

A welded hose assembly consists of several key components. The cover on a metal hose assembly protects the braid from external abrasion and can be made from many different materials including interlock casing, heat shrink covers or many types of heavy duty elastomers.

Reinforced ends are recommended for applications where sharp bends or extreme flexure occurs near the end of the hose.

A liner is recommended when the substance being transferred is abrasive or the velocity of the media is above recommended levels. The liner will facilitate smooth flow while remaining flexible, however the inside diameter will be reduced.

Metal wire braid on a hose assembly MOTION - The continuous or intermittent motion of a metal hose assembly needs to be taken into consideration when selecting components that can handle the increased stress fatigue that occurs when motion is a factor. Formulas exist that compute the amount of live hose length necessary to handle these increased demands. Random motion is unpredictable and occurs from the manual handling of a hose assembly. Care must be taken to prevent over bending the hose and to avoid external abrasion of the wire braid. Vibration is a low amplitude motion occurring at a high frequency.

Types of Motion:

AXIAL
Axial compression is the dimensional shortening of an expansion joint along its longitudinal axis, while axial extension is the dimensional lengthening of the expansion joint. This class of motion is restricted to unbraided corrugated hose only and is limited to small movements and short lengths of hose.

ANGULAR
Angular motion is the displacement of the longitudinal axis of the pump connector from its initial straight line position into a circular arc. This type of motion occurs when one end of a hose assembly is deflected in a simple bend with the ends not remaining parallel.

LATERAL
Lateral movement is the relative displacement of the two ends of a pump connector perpendicular to its longitudinal axis. This offset motion leaves the ends in a parallel plane.

Metal wire braid on a hose assembly Design Considerations
A number of factors are considered when formulating the appropriate metal hose assembly for an individual use. Standard formulas are used to identify the proper hose to use for the amount of pressure that will be exerted on the hose assembly. These include the maximum rated working pressure, maximum rated test pressure, nominal rated burst pressure, pulsating or shock pressure. Pressure/temperature correction, safety factors and pressure drop.

Design adjustments need to be made to allow for liquid or gas applications conveying medial at a high velocity. A liner is usually indicated when the gallons of flow per minute is high.

The media that will be conveyed is an important factor in the design of the metal hose assembly. The corrosion, abrasion and viscosity of the fluid have to be considered when selecting the optimum material that will have contact with the media.

Service temperature for a braided flexible metal hose has a negative affect on the amount of maximum pressure to which it can be subjected. The material from which the hose is made and the method of fitting attachment determine the maximum pressure at which an assembly can be used. The maximum working pressure must be multiplied by a correction factor for a given working temperature to determine an acceptably rated material.

Installation
Several basic principals need to be observed in the installation of a braided flexible metal hose assembly.

Avoid torque. Do not twist the hose assembly during installation. Lap joint flanges or pipe unions will minimize this condition. Two wrenches should be used in making the connection; one to prevent the hose from twisting and the other to tighten the coupling
Flexible connectors should be placed adjacent to rotating equipment in a straight line without offset. Flexible connectors installed before and after rotating equipment will help isolate the piping system from excessive vibration and noise.
To minimize the effects of vibration, install in a straight line with rigid support on the fixed end. Most machinery vibrates in a radial direction from the main shaft. The hose should be installed parallel to the shaft at right angles to the motion in expansion applications.
When major motion exists in two planes, two hoses installed at right angles to each other provide the solution.
Avoid sharp bends. Use elbows to avoid severe bends near the end of a metal hose assembly.
Maintain minimum centerline bend radius. The minimum centerline bend radius for dynamic flexing should never be less than the values in the product specification tables.

SERVICE LIFE FACTORS -
The following factors will impact the service life of metal hose assemblies:

General corrosion
High velocity/ chemical abrasives
High Cycle/ Chemical media
Stress corrosion
Intergranular corrosion/ attack
Pitting corrosion
Fatigue
High flow velocity
Torsion
Vibration
Low pressure application

BACK


	Why a Braided Flexible Metal Hose Assembly? The use of braided metal connectors for applications such as pumps, compressors and other mechanical equipment will enhance the overall operation of a system. The optimum design provides a variety of advantages: Greater flexure without fatigue Longer service life Greater capacity for pressure Increased temperature capacity of media Absorption of pump vibration and noise Acceptance of thermal expansion Reduction in pipe stress due to minor misalignment and pressure variations Reduction of stress on pumps and compressor housings, reducing long term operation and maintenance costs. Construction Corrugated Metal Hose Assemblies are usually made of stainless steel, bronze or other metals depending upon the environment in which it is being used. The corrugated hose is manufactured by forming a rolled strip into a cylindrical thin walled tube. The seams are joined by butt-welding and profile is impressed into the tube. Annular An annular configuration is one in which the convolutions on a hose consist of a series of complete circles located at right angles to the longitudinal axis of the hose. This is sometimes referred to as a bellows. An annular hose is better suited for pump connections because it can better sustain torsional stress due to longitudinal expansion from rises in pressure. Helical Helical hose is formed from a continuous spiral corrugation into tubing. This design allows for flexibility of the hose assembly under pressure and also possesses unique self-draining properties. Braid Metal wire braid on a hose assembly restrains against hose elongation under higher pressures and acts to dampen vibration. A second layer of braid may be used to increase pressure ratings. A heavy braid will also increase abrasion resistance. Optimal braid coverage will contain the core under pressure and reduce the possibility of squirm. Properly designed braid coverage will balance pressure capability with flexing requirements as well as minimize braid wear on the crown of the corrugation. Hose Assembly A welded hose assembly consists of several key components. The cover on a metal hose assembly protects the braid from external abrasion and can be made from many different materials including interlock casing, heat shrink covers or many types of heavy duty elastomers. Reinforced ends are recommended for applications where sharp bends or extreme flexure occurs near the end of the hose. A liner is recommended when the substance being transferred is abrasive or the velocity of the media is above recommended levels. The liner will facilitate smooth flow while remaining flexible, however the inside diameter will be reduced. MOTION - The continuous or intermittent motion of a metal hose assembly needs to be taken into consideration when selecting components that can handle the increased stress fatigue that occurs when motion is a factor. Formulas exist that compute the amount of live hose length necessary to handle these increased demands. Random motion is unpredictable and occurs from the manual handling of a hose assembly. Care must be taken to prevent over bending the hose and to avoid external abrasion of the wire braid. Vibration is a low amplitude motion occurring at a high frequency. Types of Motion: AXIAL Axial compression is the dimensional shortening of an expansion joint along its longitudinal axis, while axial extension is the dimensional lengthening of the expansion joint. This class of motion is restricted to unbraided corrugated hose only and is limited to small movements and short lengths of hose. ANGULAR Angular motion is the displacement of the longitudinal axis of the pump connector from its initial straight line position into a circular arc. This type of motion occurs when one end of a hose assembly is deflected in a simple bend with the ends not remaining parallel. LATERAL Lateral movement is the relative displacement of the two ends of a pump connector perpendicular to its longitudinal axis. This offset motion leaves the ends in a parallel plane. Design Considerations A number of factors are considered when formulating the appropriate metal hose assembly for an individual use. Standard formulas are used to identify the proper hose to use for the amount of pressure that will be exerted on the hose assembly. These include the maximum rated working pressure, maximum rated test pressure, nominal rated burst pressure, pulsating or shock pressure. Pressure/temperature correction, safety factors and pressure drop. Design adjustments need to be made to allow for liquid or gas applications conveying medial at a high velocity. A liner is usually indicated when the gallons of flow per minute is high. The media that will be conveyed is an important factor in the design of the metal hose assembly. The corrosion, abrasion and viscosity of the fluid have to be considered when selecting the optimum material that will have contact with the media. Service temperature for a braided flexible metal hose has a negative affect on the amount of maximum pressure to which it can be subjected. The material from which the hose is made and the method of fitting attachment determine the maximum pressure at which an assembly can be used. The maximum working pressure must be multiplied by a correction factor for a given working temperature to determine an acceptably rated material. Installation Several basic principals need to be observed in the installation of a braided flexible metal hose assembly. Avoid torque. Do not twist the hose assembly during installation. Lap joint flanges or pipe unions will minimize this condition. Two wrenches should be used in making the connection; one to prevent the hose from twisting and the other to tighten the coupling Flexible connectors should be placed adjacent to rotating equipment in a straight line without offset. Flexible connectors installed before and after rotating equipment will help isolate the piping system from excessive vibration and noise. To minimize the effects of vibration, install in a straight line with rigid support on the fixed end. Most machinery vibrates in a radial direction from the main shaft. The hose should be installed parallel to the shaft at right angles to the motion in expansion applications. When major motion exists in two planes, two hoses installed at right angles to each other provide the solution. Avoid sharp bends. Use elbows to avoid severe bends near the end of a metal hose assembly. Maintain minimum centerline bend radius. The minimum centerline bend radius for dynamic flexing should never be less than the values in the product specification tables. SERVICE LIFE FACTORS - The following factors will impact the service life of metal hose assemblies: General corrosion High velocity/ chemical abrasives High Cycle/ Chemical media Stress corrosion Intergranular corrosion/ attack Pitting corrosion Fatigue High flow velocity Torsion Vibration Low pressure application BACK
	©2001 River Bend Hose Specialty, Inc. 800-727-5043 sales@riverbendhose.com