Hydraulic Systems and Applications

References

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

Hydraulic Mechanical AdvantageF2 =

F1 = 20 lbf

A1 = 2 in2

A1 = 20 in2

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

Questions?