Hydraulics And Pneumatics Lecture

Pneumatics

Branch of liquid power systems that uses compressible fluid to transfer energy

Pascal’s law

Pressure on a fluid is spread evenly in all directions and perpendicular to the containing surfaces

Hydraulics meaning

Incompressible liquid that has slow, smooth, motion

Pneumatics characteristics (6)

1. Compressible gas 2. Quick motions 3. Not as precise as hydraulics 4. Lubricant must be added 5. Reduces component wear 6. Cleaner than hyd. 7.lower pressure

Pneumatic transmission power is like

Pushing on spring (input) to get power (output)

Aircraft pneumatic system characteristics

-operates like hyd sys. Except uses AIR to transmit power - compressible

Pneumatic systems can be used for

Brakes, opening and closing doors, driving hydraulic pumps, alternators, starters, water injection pumps

Pneumatic system relationship between pressure and volume = result

High pressure+low volume=high pressurized air

ACFT Hydraulic systems may use compressed air as

Back up source of power in event of hydraulic systems failure, de-icing, vacuum pumps, cabin pressurization

High pressure systems air stored in metal bottles diagram

Charging valve, control valve

Charging valve

Allows airs to be added to the bottle

Control valve

Acts as a shutoff valve

Why bottled pressure systems suck

Not rechargable during flight, limited usage bc small quantity

When are high pressurized air bottles used for

Emergency operations, landing gear, brakes

What will a compressor do to a high pressure system bottle

Recharge the bottle during flight

Pneumatic system do not use

-reservoir

-hand pumps

-accumulators

-regulators

-engine/electronically driven power pumps

How does pascal apply to the advantage of using hydraulic systems in plane

If a number of passages exist in a system, pressure is distributed through all of them

Viscosity

Internal resistance to flow

Viscosity increases as temp

Decreases

A hyraulic fluid is good in terms of viscosity why

Enough thickness to give a good seal at pumps, valves, pistons, and wont resist flow

What is used to measure viscosity

Viscosimeter

How does saybolt viscometer measure viscosity

Measures time needed for 60 mil at 100F to pass an orifice

Chemical stability meaning in hydraulics

Ability to resist oxidation and deterioration through time and temp.

Why is temp of liquid alone in reservoir of a system not always true state of operating conditions

Hot spots on bearings, gear teeth

What results in continuous passage of hot spots in systems

Temps so high enough to ruin liquid

Liquids with high viscosity have a greater wat compared to what

Resistance to heat than low-viscosity liquids

Average hydraulic liquid typically has what kind of viscosity

Low viscosity

Flash point

The temp where liquid gives off vapor enough to ignite a flash with a flame

A good hydraulic fluid has a ____ flash point because

High bc indicated good resistance to combustion and evaporation at norm. Temps.

Fire point

Temp where gives off enough vapor to burn when exposed to flame

Is fire point desirable for a good hydrualic fluid

Yas

Why are different hydraulic fluids used

To avoid damage to nonmetallic stuff in hyd. Sytems

Three main types of hydraulics fluids

Minerals, polyaplhaoefins, phosphate esters

MIL-H-5606

Oldest mineral oil ,used where low fire hazard,processed w petrol,red

MIL-H-6083

Rust-inhibitor version of MIL-H-5606 thus intechangeable

MIL-H-83282

Fire-resisant polyalphaolefin , made bc MIL-H5606 burns, high viscosity at low temps.

MILH83282 is limited to what temp

-40F

MILH83282 can be used interchangeably with

MILH5606

MILH46170

Rust-inhibitor version of 83282

Phosphate ester fluid #1 characterisitc

Extremely fire resistant

Phosphate Ester two main examples

SKydrol and Hyjet

Class 1 fluids of Type IV characterisitcs

-low density - weight saving -

What are the other types of phosphate esters fluid besides the name brands

Type IV and V

Class II fluids of type IV charactarticis

Standard density

Phosphate ester fluid should never be mixed with

Petrol-based fluid

Phosphate ester is rlly good bc

Fire-resistant, no metal effect

What paints are resistant to phosphate esters fluid

Epoxies and polyurethanes

Hyrdraulics must be paired with the right set of..se

Seals,gaskets, and hoses

Phosphate ester fluids should never be inside this fluid’s seals

Neoprene or Buna-n

Two main ways hydraulic fluid is contaminated

Particles, non-abrasives

Contamination checks

-check filters - samples to find to location exact contamination

3 situations where u should sample hydrualic fluid for contamination

Routine sampling, unscheduled maintenance, suspicion of contamination

What is 1st thing you do in sampling hydraulic procedure

Operate hydraulic sys for 13 mins to flow hyd. Fluid around

What u do after u have system on for 13 mins

Shut down and depressurize

What u do after depressurize hyd system

Clean sampling loco with lintless cloth

What u do after cleaning sampling loco

Place trash under reservoir drain valve and open valve for 1 pint of fluid

What u do after you u drain 1 pint to trash

Put clean sample bottle under fluid stream and fill and close drain valve

What u do with the hyd fluid filled sample bottle

Write important info + replace the lost fluid

To avoid contamination, is good to make sure

Every item is cleaned when used

To control specific contamination what is added on lines of hyd fluid sys

Filters on pressure,return line, and pump

What are seals used for

To prevent fluid from passing a certain point + keep air and dirt out

Packings and gaskets are used in hyd systems to meet

diff speeds and temps

List all types of Seals

Packings, gaskets,wipers o-ring, v-ring, u-ring

Packing

Hyd seal used internally on a sliding or moving assembly

Gaskets are used in what circumstance

Used between nonmoving fittings and bosses

AN6225

V ring packing = one way seal installed with open end v facing pressure

What is different between the V-ring world

Theres a female and male adapters

V rings have what kind of reqiurement when installed

Torque seal retainer to necessary amount

What is U ring code number

AN6226

U rings are used mostly

Used in brake assemblies and brake master cylinders

Specific characteristic for U ring seal

Seals pressure only one direction = lip must face pressure

U rings are used under what psi

1000 psi

Whats the popular choice of seal ring

O ring

What are two main o ring number codes

MS28775 and MS28778

Color codes on o rings are to tell

What ring goes with what fluid

Blue o ring means

Compatitable with MILH5606

Green stripe on o rings means

Works with phosphate esters fluid

Hydrocarbon o rings are never the color

Blue

Backup rings code #

MS28782

How to tell a back up rings o-ring usagr

Dash #

BAck up ring characteristics of usage

-unaffected by fluid or vapor - tolerate high temps+pressures

Who owns all the backup rings

Teflon

Inspection of a backup ring should look like

Ensuring surface clean, edges sharp,and scarf cuts parallel

How should backup rings be installed

Downstream of O ring

What are gaskets used for

Used as static (stationary) seals between two flat surfaces

What are common gasket materials

Asbetos, copper, cork, rubber

When are asbestos sheeting used as a gasket

When a heat resistant gasket needed, Used for exhaust system gaskets

What is commonly added to asbestos exhaust gaskets to prolong their life

Thin sheet of coper edging

What is a solid copper washer used for

Used to spark plug gaskets when incompressible, semi-flexible gasket is needed

When cork gaskets be used

Oil seal between engine crankcase and other stuff

Why can cork gaskets be useful on uneven or varying surfaces

Cork can occupy many spaces caused by rough change

When can rubber sheeting be used as a gasket

When compressible gasket is needed

Where should rubber sheeintg NOT be used

Where it makes contact with gasoline/oil bc rubber ruins rapidly when exposed

Where are gaskets used in fluid system

Around end caps of actuating cylinders, valves,

What shape is the gasket generally used around actuating cylinder, valves, and other units

Shaped like O-ring, similar to O-ring packings

What are most seals made from

Synthetic materials that are compatible with hydraulic fluid being used

Why’s it important for seals to be compatible with hydraulic fluid

Using seals that are incompatible with hyd fluid = cause leaks/malfunction

What type of seals are used with MILH5606 hyd fluid

Neoprene/ BUna-n

What are MILH5606 seals not compatible with

Phosphate ester fluids

What materials are used for seals with phosphate esters based fluids

Butyl rubber