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Required•Introduction to Naval Engineering (Ch 15)Optional•Principles of Naval Engineering (Ch 3 pp 64-74)
Objectives
A. Comprehend Pascal’s Principle and its applicability to hydraulic theory.
B. Comprehend the method of determination of output when given a hydraulic system configuration and input.
C. Comprehend the basic operation, principal components, and safety considerations related to hydraulic systems.
• Primary control boosters • Retraction and extension of landing gear • Sweep back and forth of wings • Opening and closing doors and hatchways • Automatic pilot and gun turrets • Shock absorption systems and valve lifter systems • Dive, landing, speed and flap brakes • Pitch changing mechanism, spoilers on flaps • Bomb bay doors and bomb displacement gears
Introduction/Uses
• Hydraulic power was harnessed as far back as 6000 BC– China– waterwheel to power bellows on a blast
furnace• Hydraulics used in many marine applications:– Steering/control systems (rudder, planes)– Deck machinery (anchor windlass, capstans, winches)– Masts & antennae on submarines– Weapons systems (loading & launching)– Other: elevators, presses
Advantages• Convenient power transfer– Few moving parts– Low losses over long distances– Little wear
• Flexibility– Distribute force in multiple directions– Safe and reliable for many uses– Can be stored under pressure for long periods
• Variable speed control– Quick response (linear and rotary)
Disadvantages
• Requires positive confinement (to give shape)• Fire/explosive hazard if leaks or ruptures• Filtration critical - must be free of debris• Manpower intensive to clean up
Hydraulic Theory
• Hydraulics – Covers the physical behavior of liquids in
motion– Pressurized oil used to gain mechanical
advantage and perform work• Important Properties– Shapelessness– Incompressibility– Transmission of Force
Important Properties• “Shapelessness”– Liquids have no neutral form– Conform to shape of container– Easily transferred through piping from one location to
another • Incompressibility– Liquids are essentially incompressible– Once force is removed, liquid returns to original
volume (no permanent distortion)• Transmission of Force– Force is transmitted equally & undiminished
in every direction -> vessel filled with pressure
Hydraulic Theory
• Pascal’s Law– Magnitude of force transferred is in direct
proportion to the surface area (F = P*A) or Pressure in a fluid acts equally in all directions
– Pressure = Force/Area• Liquid properties enable large objects (rudder,
planes, etc) to be moved smoothly
PUMP
PUMP
PUMP
BY PASSVALVE
BY PASSVALVE
BY PASSVALVE
FILTER
FILTER
FILTER
HYDRAULIC
POWER-PLANT
RETURNHEADER
CHANGE 3
SUPPLYHEADER
SUPPLYHEADER Accumulator
Air Cylinders
Basic Hydraulic System
• Hydraulic Fluid– Usually oil (2190 TEP)- non-corrosive, lubricant,
already in use onboard• Pressure Source– Hydraulic pump (A-end of system)
• Pressure user– Hydraulic motor (B-end of system)
• Piping system (w/ valves, tanks, etc)– Get fluid from A-end to B-end
Hydraulic Pump (A-End)
• Pumps can be positive displacement or centrifugal
• Waterbury pump• Variable-stroke piston pump
• Tilting box can tilt fwd/aft while pump rotates
• Angle of tilting box determines capacity and direction of oil flow
Hydraulic Pump (A-End)• Waterbury pumps are popular because the direction and volume of flow can be altered without changing the speed or direction of the prime mover.
Cylinder/Motor (B-end)• Piston/cylinder used if desired motion is
linear– Hydraulic pressure moves piston & ram– Load is connected to ram (rudder, planes,
masts, periscopes)Piston Cylinder RAM
Hydraulic Fluid Supply/Return Ports
Seal
Cylinder/Motor (B-end)
• Motor used if desired motion is rotary– Essentially a variable-
stroke pump in reverse– Used for capstan,
anchor windlass, etc
Piping System
• Has to withstand excessive pressure• Valves, filters, & HX’s all necessary• Accumulators– Holds system under pressure (w/out contin. pump)– Provides hydraulics when pump off/lost– Compensates for leakage/makeup volume– Types: piston, bladder, & direct contact
Accumulator Types
• Piston– Most common
• Bladder – Gun mounts– Steering
systems
• Direct contact– Least common
SUPPLY
RETURN
VENT&SUPPLY
TANK
AIR
HYDRAULIC-POWERED HYDRAULIC SYSTEM
TO SYSTEM
CONTROLVALVE
CONTROLVALVE
SIMPLEX PUMPS
HYDRAULICRETURN
Electrohydraulic Drive System
• Uses hydraulics to transfer power from electric motor to load
• Rotary: Waterbury pump connected to rotary piston hydraulic motor (speed gear)– Tilting box of A-end controls direction/speed of B-end– Adv: high starting torque, reversibility, high power-to-
weight ratio
• ex: Electrohydraulic Speed Gear or Steering Gear– capstan, anchor windlass, cranes, elevator, ammo hoist
Electrohydraulic Steering Gear
• Same as speed gear except B-end is a hydraulic cylinder to produce linear motion
• Waterbury pumps connected by piping to hydraulic ram cylinder– Various methods for connecting rams to tillers– Two pumps for redundancy & reliability– Movement of steering wheel through hydraulic
system moves rudder
Control of System
• Remote control– Normal method– Control from bridge
• Emergency– Take local control– Manually position control surface/rudder
Take Aways
• Describe Pascal’s theory and apply it to mechanical advantage problems
• Describe the properties of oil and how they are advantageous in hydraulic applications
• List three types of accumulators. Describe the purpose of an accumulator.
• Give the advantages and disadvantages of hydraulic systems
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