Hydraulics is the study of fluids at rest or in motion, especially regarding engineering applications. Hydraulic systems use pressurized fluids to gain mechanical advantage and perform work. Basic hydraulic systems include a hydraulic pump to pressurize fluid, a hydraulic motor or cylinder to use the pressurized fluid to do work, and piping to transfer fluid between components. Hydraulic systems provide convenient power transfer with few moving parts and flexibility to distribute force in multiple directions for many uses.

1. HydraulicsHydraulics
hy·drau·lics [hy·drau·lics [h drólliksh drólliks ]] nounnoun
study of fluids: the study of water orstudy of fluids: the study of water or
other fluids at rest or in motion,other fluids at rest or in motion,
especially with respect to engineeringespecially with respect to engineering
applicationsapplications

2. ObjectivesObjectives
• Behavior of liquids & theory of operation
• Basic hydraulic system components
• Advantages & disadvantages of hydraulics
• Electrohydraulic systems including speed
gears & steering gears

3. Introduction/UsesIntroduction/Uses
• Hydraulics used in many applications:
• Steering/control systems (rudder, planes)
• Deck machinery (anchor windlass, capstans,
winches)
• Masts & antennae on submarines
• Weapons systems (loading & launching)
• Other: elevators, presses

4. Hydraulic TheoryHydraulic 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

5. Important PropertiesImportant Properties
• ““Shapelessness”Shapelessness”
• Liquids have no neutral form
• Conform to shape of container
• Easily transferred through piping from one location to
another
•
IncompressibilityIncompressibility
• Liquids are essentially incompressible
• Once force is removed, liquid returns to original
volume (no permanent distortion)
•
Transmission of ForceTransmission of Force
• Force is transmitted equally & undiminished
in every direction -> vessel filled with pressure

6. Hydraulic TheoryHydraulic Theory
• Pascal’s Law
• Magnitude of force transferred is in direct
proportion to the surface area (F = P*A)
• Pressure = Force/AreaPressure = Force/Area
• Liquid properties enable large objects
(rudder, planes, etc) to be moved smoothly

7. Hydraulic Mechanical AdvantageHydraulic Mechanical Advantage
F2 =
F1 = 20 lbf
A1 = 2 in2
A1 = 20 in2

8. Basic Hydraulic SystemBasic Hydraulic System
• Hydraulic Fluid
• Usually oil (2190 TEP)
• 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

9. Hydraulic Pump (A-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

10. Hydraulic Pump (A-End)Hydraulic Pump (A-End)
•Variable-stroke piston pump
•Tilting box can tilt fwd/aft while pump rotates
•Angle of tilting box determines capacity and dir. of flow

11. Cylinder/Motor (B-end)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)
PistonPiston CylinderCylinder
RAMRAM
Hydraulic Fluid Supply/Return PortsHydraulic Fluid Supply/Return Ports
SealSeal

12. Cylinder/Motor (B-end)Cylinder/Motor (B-end)
• Motor used if desired
motion is rotary
• Essentially a variable-
stroke pump in reverse
• Used for capstan,
anchor windlass, etc

13. Piping SystemPiping 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

14. Accumulator TypesAccumulator Types
• Piston
• Most common
• Bladder
• Gun mounts
• Steering
systems
• Direct contact
• Least common

15. AdvantagesAdvantages
•
Convenient power transferConvenient power transfer
• Few moving parts
• Low losses over long distances
• Little wear
•
FlexibilityFlexibility
• Distribute force in multiple directions
• Safe and reliable for many uses
• Can be stored under pressure for long periods
•
Variable speed controlVariable speed control
• Quick response (linear and rotary)

16. DisadvantagesDisadvantages
• Requires positive confinement (to give
shape)
•
Fire/explosive hazard if leaks or rupturesFire/explosive hazard if leaks or ruptures
• Filtration critical - must be free of debris
• Manpower intensive to clean up

17. Electrohydraulic Drive SystemElectrohydraulic 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

18. Electrohydraulic Speed GearElectrohydraulic Speed Gear

19. Electrohydraulic Steering GearElectrohydraulic 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

20. Electrohydraulic Steering GearElectrohydraulic Steering Gear

21. Control of SystemControl of System
• Remote control
• Normal method
• Control from bridge
• Emergency
• Take local control
• Manually position control surface/rudder