Fluid

Chapter 8

Fluid Storage and Distribution
Reservoirs, Conductors, and Connectors

Objectives
 Describe the function of the hydraulic system reservoir and identify the primary design features involved in its construction.  Explain the factors that must be considered when establishing the size of a reservoir for use in a system.  Describe the factors that are basic to the design and structure of fluid conductors used in hydraulic systems.
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Objectives
 Compare and contrast the various types of pipe, tubing, and hose used in hydraulic systems and explain the ratings for each conductor.  Identify and explain the factors that must be considered when selecting a conductor for use in a hydraulic system.  Explain the information typically found on data sheets provided by the manufacturers of hydraulic system pipe, tubing, and hose.
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Reservoir
 The primary purpose of the reservoir is to hold the system fluid not currently in use in the system  Other important functions of the reservoir are:
– – – – Remove heat Separate solid particles Release air from fluid Separate water from fluid
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Reservoir
 The reservoir serves many functions

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Reservoir
 The typical hydraulic system reservoir is a rectangular, covered steel tank  The tank is typically fitted with:
– – – – – – Pump inlet line System fluid return line Drain line Filler cap Air breather Fluid-level indicator
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Reservoir
 Baffles are used in the interior of reservoirs to direct flow to maximize the distance the fluid must travel between the return line and the pump inlet line
– Slows the movement of the fluid – Increases cooling – Increases separation of solid particles, air, and water

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Reservoir
 Baffles are typically included in a reservoir

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Reservoir
 Typical reservoir construction

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Reservoir
 L-shaped and overhead reservoir designs may be used in systems where positive pressure is needed on the pump inlet line

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Reservoir
 L-shaped reservoir

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Reservoir
 Overhead reservoir

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Reservoir
 In special situations, the system reservoir may be:
– Cavities in large machines – Gear cases in mobile equipment

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Reservoir
 As a general rule, the capacity of the reservoir should be three times the rated flow of the pump
– Fixed installations may be higher – Mobile applications, where weight and space are factors, may be less

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Conductors
 The proper selection, installation, and maintenance of conductors is critical to efficient hydraulic system operation

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Conductors
 Pipe, tubing, and flexible hose are considered basic conductors in a hydraulic system

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Conductors
 Conductors must have:
– Adequate strength to withstand high system pressures – Low flow resistance to assure low energy loss during system operation – A design that allows economic installation and low maintenance

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Conductors
 Conductors must not only withstand normal system operating pressure, but also hydraulic shock pressures  Shock pressures result from kinetic energy in the system when:
– Directional control valves are shifted to reverse the movement of a load or heavy machine member – Actuators encounter sudden load changes

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Conductors
 Low flow resistance requires a conductor with an inside diameter large enough to allow the needed volume of fluid to move through the line within recommended fluid velocities

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Conductors
 Restrictions may cause turbulent flow

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Conductors
 Flow resistance in a system results from resistance to fluid flow caused by:
– – – – – Surface of the conductor Bends and fittings in the lines Orifices in components Turbulence in the fluid stream Viscosity of the fluid

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Conductors
 Fluid flow resistance resulting from fluid movement through conductors and other system components:
– Lowers the work output of a system – Produces heat, which may cause operating problems

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Conductors
 Future maintenance must be carefully considered when designing and installing hydraulic system conductors to assure minimal difficulty in removing components for service

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Conductors
 Pipe in a hydraulic system should be:
– Seamless, black pipe – ANSI schedule rating of 40, 80, or 160, depending on the maximum pressure expected in the system

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Conductors
 Various nominal pipe dimensions

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Conductors
 Schedule number indicates wall thickness

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Conductors
 Tubing:
– Is a relatively thin-walled, semirigid conductor – Can be bent and shaped into lines that provide good flow characteristics with a minimum of visual clutter

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Conductors
 Tubing can be bent, unlike pipe

Used with permission of CNH America LLC © Goodheart-Willcox Co., Inc.

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Conductors
 The size of tubing is indicated by the actual outside diameter
– Inside diameter varies according to wall thickness – Most tubing is manufactured to the specifications of a standardizing organization such as ANSI or SAE

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Conductors
 Hose is a flexible conductor made up of:
– Inner tube to conduct the fluid – Middle layer of reinforcing material for strength – Outer protective coating to withstand abrasion and abuse

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Conductors
 Hose with braided-wire middle layers

Gates Corporation

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Conductors
 Hose with spiral-wound-wire middle layers

Gates Corporation

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Conductors
 Hose provides flexibility

Used with permission of CNH America LLC

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Conductors
 A wide variety of hoses are available, often making selection difficult  Standardizing organizations provide guidelines that help compare various products on the market

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Conductors
 Manifolds are machined or fabricated parts used to distribute system fluid  They are often used to help produce a lighter, more-compact system

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Conductors
 A wide variety of fittings are available to assist in attaching conductors to system components such as:
– – – – Reservoir Pump Valves Actuators

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Conductors
 Careful selection of fittings can:
– Help control construction costs – Improve system efficiency – Allow easier system maintenance

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Conductors
 Dryseal standard pipe threads should be used on pipe fittings, rather than standard pipe threads, to assure a tight thread seal that will not leak under high system pressure

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Conductors
 Standard pipe threads

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Conductors
 Dryseal standard pipe threads

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Conductors
 Fittings with pipe threads or straight threads sealed with an O-ring or a metal compression washer are typically used to attach tube and hose to hydraulic components  Tubing is attached to fittings by flaring the tube, compression, soldering, or brazing

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Conductors
 Hose attached to an actuator with elbow fitting and adapter with pipe threads

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Conductors
 Hydraulic systems typically use a 37° flare angle

Gates Corporation

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Conductors
 Compression fittings use an O-ring, ferrule, sleeve, or patented configuration to provide the seal

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Conductors
 Soldered or brazed fittings usually use split flanges to mount the fitting to the component

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Conductors
 Metal hose-end fittings are used to connect flexible hose to the components of the system
– Available in both permanently attached or reusable styles – Attached to the components using pipe threads, flare fittings, or split flange fittings

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Conductors
 Reusable hose-end fittings are either:
– Screw-together type – Clamp type

 These fittings can be assembled to the hose using basic hand tools, which allows field assembly

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Conductors
 Permanently attached hose-end fittings are crimped or swaged onto the hose  Special equipment is required to install this type of fitting on a hose

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Conductors
 Crimped hose-end fittings

Gates Corporation

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Conductors
 Swaged hose-end fitting

Gates Corporation

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Conductors
 A wide variety of adapter fittings are available for making proper connections between conductors and system components:
– Transitions from one thread type to another – Elbows at 45° and 90° – Swivels that allow component movement

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Analysis of Circuit and System Operation
 Properly selecting a conductor requires an examination of not only the hydraulic system, but also the mechanisms operated by the system  Factors that must be considered are:
– – – – Pressure requirements Flow requirements Vibration Required movements of machine members
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Analysis of Circuit and System Operation
 When selecting a conductor for a system, consider pressure:
– Normal system operating pressure – Shock pressures

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Analysis of Circuit and System Operation
 Flow velocity must be carefully considered when selecting a conductor for a system
– Pump inlet line average fluid velocity should not exceed 4 ft/sec – Working line fluid velocity should not exceed 20 ft/sec

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Analysis of Circuit and System Operation
 Low pump inlet velocity prevents excessively low pressure in the line
– Too low of a pressure can lead to pump cavitation – Cavitation can cause serious pump damage

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Analysis of Circuit and System Operation
 Excessively high working line velocity will produce turbulent flow
– Turbulent flow can cause high flow resistance – High resistance results in increased system operating temperatures

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Analysis of Circuit and System Operation
 Very high and very low temperatures can adversely affect the service life of a hose  Continuous system operation at or above recommended temperatures can cause damage

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Analysis of Circuit and System Operation
 Hose must be rated for the system operating temperature

Used with permission of CNH America LLC

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Interpreting Data Sheets from Manufacturers
 Data sheets are available from the conductor manufacturer
– Good source of information – Include a full range of information about a conductor:
• Construction details • Typical applications • Technical data related to pressure, flow capacity, and temperature tolerance

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Conductor Installation
 When installing pipe and tubing, it is important to have the correct lengths
– Should not be distorted – Should not be placed under tension – Distortion and tension can result in material fatigue and lead to part failure

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Conductor Installation
 When installing tubing, the number of fittings in a system can be reduced by bending the tube where possible  Hand tools and power equipment are available to produce accurate bends

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Conductor Installation
 Long lengths of pipe and tubing should be supported by brackets or clamps to secure the conductor  This will reduce fatigue caused by conductor weight or system vibration

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Conductor Installation
 System pressure changes will change the length and diameter of a hose
– Allow slack in the hose – Allow adequate hose-to-member clearances

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Conductor Installation
 Allow slack in hose when it is installed

Gates Corporation

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Conductor Installation
 When hose is installed, ensure it is not twisted

Gates Corporation

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Conductor Installation
 When assembling hydraulic system conductors and their associated fittings and adapters, the result should:
– Be a neat and uncluttered conductor layout – Efficiently distribute fluid throughout the system

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Conductor Installation
 A clean and efficient conductor installation

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Review Question
The component that is designed to hold the fluid not currently in use in the system is called the _____. reservoir

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Review Question
What are the two reservoir configurations that are suitable for use with a pump that requires a positive pressure on the inlet line? A. L-shaped and B. overhead

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Review Question
List the three basic categories of fluid conductors used in hydraulic systems.

A. Pipe, B. tubing, and C. flexible hose.

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Review Question
American National Standards Institute (ANSI) schedule numbers identify the _____ of pipes.

wall thickness

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Review Question
List three factors assured by the proper selection and installation of pipe, tube, or hose fittings in hydraulic systems. A. Reasonable initial construction cost, B. efficient system operating, and C. minimal ongoing maintenance.

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Review Question
Name four situations that may result if conductors and fittings are not carefully selected for a given hydraulic system.
A. Conductors may cost more than necessary, B. inefficient system operation, C. parts may prematurely fail, and D. disassembly may be more difficult than necessary during service.

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