Hydraulics

Objectives
Behavior of liquids & theory of operation
Basic hydraulic system components
Advantages & disadvantages of hydraulics
Electrohydraulic systems including speed gears & steering gears

Introduction/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

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)
Pressure = Force/Area
Liquid properties enable large objects (rudder, planes, etc) to be moved smoothly

Hydraulic Mechanical Advantage

Basic 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

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)
Variable-stroke piston pump
Tilting box can tilt fwd/aft while pump rotates
Angle of tilting box determines capacity and dir. of flow

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

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

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 Speed Gear

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

Electrohydraulic Steering Gear

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