HYDROLICS general Flashcards

Question

Choice of aircraft hydraulic fluids is influenced by...

Answer 1

materials of seals, rings, seats, etc.

Answer 2

**Mineral & synthetic** **DTD 585 - mineral:** petroleum/mineral based red in colour works with synthetic rubber seals (Neoprene) **Skydrol - synthetic:** Phosphate ester based oil works with syntheitc rubber seals (Butyl & teflon) Type 500A & B - FRESH = purple colour Type 700A = green

Answer 3

**Only one type of oil can be used **in the system **incorrect one is added **- seals will damage - fluid leakage occurs internally and externally in actuators **How to know if the wrong fluid is added?** - fluids have their own colour - can be confrim by AC manual - use fluid from sealed containers

Answer 4

Low: up to 2000psi High: Above 2000psi and avg 3000-4000psi A380 operates at 5000psi

Answer 5

the actuator can be made small, meaning less fluid is required and pipes can be smaller weights less and saves space Disadvantage: can cause shear

Answer 6

****good for **light/mid aircrafts **that don't require constant pressure esp if **flaps and gear are powered for short time** **works for Active systems generate pressure only when it's demanded by the service** **simple** system but only **one service can be operated at a time** **low pressure **of 2000psi **how it works: IF a service is not selected:** fluid passes from reservoir then thru the pump fluid passes through the valve (past the NRV) and into the selector(s). If service is not operating or selected, then fluid continues to move through the valves and return to reservoir **here we are at lowest pressure, but fluid still moves to lubricate the pump** **if a service is selected** fluid passes from reservoir then thru the pump fluid passes through the valve (past the NRV) and into the designated selector (belonging to the service). If service is selected, then fluid goes through one side of the Actuator (piston moves). From the other side of the actuator, the fluid flows into the other selector, returns back thru the valves, and back to resourvoir **here we are at high pressure** Selector returns to 'neutral' to offload the pump and allow other services to be selected. The relieve valve will relief pressure if the selector is not returned to it's neutral posisition.

Answer 7

Use on **large aircrafts** **multiple services can be operated at same time** **the use of this system is only limited by the flow capacity of the pump.** pressure in this system stays limited to the part of teh system that leads to the selector valves. So there is a lot of pressure and load on the pump. **Need to relief the pump from this pressure by:** **1.Off loading valve:** allows pump to unload while service is not being used 2. ACOV In a fixed volume pump, an automatic cut-out valve is fitted (ACOV) to divert pump output to the reservoir when pressure has reached normal operating pressure Option 2: In other system a Variable volume pump is used. This reduces fluid delivery flow as pressure increases Once operation is complete, there is no need to return the selector valve to neutral because the pump system is designed to relieve pressure increase. But in some system,s the selector valve might be returned to neutral = hydrolic lock (fluid is locked on both sides of the actuator) and non return valve, hence no undemanded moved will be done by the actuator and piston cannot move In some simple aircrafts: A simply hydrollic power pack is used this is an electric pump operated by pressure operating switch - with a reservoir and accumulater it's when

Answer 8

**space to store fluid. ** **fins and baffles** help reduce swirling of fluid when aircraft is moving **supplies fluid to the pump** **Stores extra to compensates for small leaks** **has extra airspace to account for Actuator fluid coming back and thermal expansion **Reservoirs are pressurized:** 1. **to avoid fluid from boiling at altitude** 2. **provides positive pressure at inlet to the pump to to avoid bubbles in fluid (cavitation) in altitulde** Reservoirs are pressurized to ensure pump inlet is provided with continious and adequate supply of fluid free of foam the **fluid coming in**, flows thru a **'de-arator to remove the bubbles** has **relief valve** to relieve **over pressure** May have a **temperature & content sensor ** In case of major fluid loss, there is a **2nd lower exit pipe** operated by **a hand pump **to acompany the main pump, so i**n case fluid is not supplied by main pump**, a reserve of fluid is available for the heand pump ----- **Fluid level depends on:** * **Thermal expansion** = higher temp, **fluid expands** * When system is **energized (pump starts pumping**) = **fluid decreases** * When actuators are operated **= fluid fluctuates**

Answer 9

Fitted for both Sucktion and Pressure lines (both sides of the pump) -----One for protecting the pump -------One for keeping fluid clean and remove particles (protect seals) some other individual components may be fitted with their own filters. **has pressure differential sensor that lights up/visual indicator that indicates it is clogged** sometimes there is a r**elieve valve to allow unflitered fluid to pass** if system is clogged note: i**ndicator can light up if fluid has high viscocity in low temp**

Answer 10

**NRV -** * prevents reverse flow of fluid * a ball push by fluid pressure against the spring. * when pushed, it allows fluid into the valve * when pressure is reduced, and fluid has moved on, the ball returns back to its place to close the valve **selector valve:** directs pressure to the appropriate side of the accutator. Mechanical or electrical driven **Pressure relieve valve** Dumps excess pressure into the resrvoir

Answer 11

Closed Centre Selector Open Centre Selector Linear Valve Selector

Answer 12

**Driven from:** accessory gearbox **Usually called:** Engine driven pumps **Pumps can be:** * **Constant delivery Fixed volume** * **Constant pressure Variable volume** **Piston type**: for large aircraft **rotary/spur type** for small aircraft Pressurizes fluid flow in the circuit *has overheat detection draws oil from reservoir and delivers a supply of fluid to the system **Can be:** * *hand operated * engine driven * electric motor driven (used for light aircraft power pack or for emergency) * ATM - air turbin motor (pneumatically operated) * RAT - ram air turbine * PTU - power transfer unit (hydraullical pumps) **ATM, RAT, PTU - provide and alternate supply for an Engine driven pump as part of hydraulic system redundancy provision in the event of engine pump failure** **RAT**: provides **emergency** hydraulics and electric power to **flight controls and breakls only**

Answer 13

**hand pump used in small aircrafts** **in large aircraft used in:** 1. for ground servicing to take place without engine running 2. for lines and joints to be tested 3. cargo doors to be operated witout power **Hand** pump is usually - a **double acting pump- delivers oil on 2 strokes** - **Non return valve - relief valve (to relieve pressure = 10% of normal system pressure** In the centre of the piston assembly, there is a Trasnfer Valve, which is spring loaded to the closed position. HOW IT WORKS * Fluid transfers from reservoir via the Inlet, where the RV1 sits. * Fluid then travels to the Piston assembly. * When the operating handle is moved up, * It push the Piston assembly down * this increases pressure below the piston and holds the RV1 closed. * Fluid is trapped between the RV and Under the piston, which builds up pressure * It is felt by the transfer ball at the bottom of the transfer valve * which pushes the ball up towards the transfer valve up, creating a gap for the fluid to move up the piston * then fluid flows out the RV2 outlet * Once the piston moves to the bottom of its travel, the handle moves in the opposite direction, * moving the piston in the assembly up * As the piston moves up, the pressure above the piston incerases * the ball is pushed into the transfer valve, closes the transfer valve * Pressue above the piston is great, pushing fluid to RV2 outlet * RV1 opens up becuase of suction felt below the piston, allowing fluid to flow from reservoir

Answer 14

**1) Constatn delivery (fixed volume) pump for low hydraullic pressure aircrafts** * Uses spur rotary gears. They rotate at constant speed * Therefore they supplies fluid at a constant rate * Volume of fluid passing depends on the speed of rotation * Needs an automatic cut-out to control it's output or relief valve to return the fluid to the reservoir * when the system is not operating, it requires an idling circuit. This pump is usually a single or double stage gear pump giving a large flow at a small pressure, typically up to 2000 psi. * delivers same amoutn of fluid without regard to the fluid required by the system, unused fluid returns to reservoir via relief valve * wastes energy Made with 2 gears. 1 gear driven by the power source (ie engine), Gear 2 is powered by gear 1 the 2 gears rotate fluid travels from inlet, through the gear teeth, then out from the outlet Ths system gives great flow rate but Low pressure rate This system supplies fluid at constant rate irrespective of demand If this system is mechanically driven by the engine in a 'closed hydraullic system', it needs an ACOV to return fluid to the reservoir when the system is not operating **Constant Pressure (variable volume) pump for high pressure hydraullic system modern aircrafts** * large modern aircraft (for hydraulic systems operation at 3000 psi +) * supplies fluid at a variable volume - on demand * controls its own pressure * can alter the outlet flow as more services are operated. It will increase flow to maintain working pressure * ACOV and accumulator not needed

Answer 15

Constant pressure pumps Demand pressure pumps (better option)

Answer 16

Used in Constant Deliver (fixed volume) engine driven pumps. in there, it controls system pressure it also provides the pump with idling circruit when no service is selected however for this reason, it needs an accumulator to maintain pressure, and take in some slight leakage due to the frequent operation of the 'cut - out' maintains cooling and lubrication of output pumped fluid --HOW IT WORKS-- when the cut out is in possition, fluid goest thru the pump, then thru the NRV. Pressure is built, till it pushes the piston upwards till the poppet valve opens and the output pumped fluid passes to the reservoir

Answer 17

The time between cut-out (off load) and cut-in (on load) (periodicity) of the ACO valve

Answer 18

* cause a **reduction in the operating period **with **frequent loading and unloading of the pump**; * also with a l**oss of system fluid.**

Answer 19

* caused by a **piston seal failure** * causes **frequent loading and unloading** of the pumps * **increase in fluid temperature.** * **Decrease system pressure** Note: **No fluid loss**

Answer 20

**Contains:** Has piston moving freely inside a sealed cylinder onse side has gas (precharged nitrogen or air), and other has fluid **How it works** *works as an energy storage When hyraulic system pressure increases the piston moves up and compresses gas the piston stops when gas pressure = fluid pressure and remain in this state during normal operations If hydraulic pump fails, the accumulator has 'reserve/limited supply of pressure fludi' to operate essential services **when it's powered:** it **shows hyrdraulic system pressure** **when it's not powered**: it **shows nitrogen pre-charge pressure** **Inciorrect recharge:** will cause hammering in the system affect the placement of the piston inside accumulator **If in excess:** then there is insufficient fluid stored **if low:** insufficient fluid pressures for emergencies **needed for:** * breaking system * allowing thermal expansion * allow internal small leaks * store pressurized hydraulic fluid/gas & dampen pressure pulses fluctuation * provide emergency supply of fluid in case of pump failure * prolongs the period between cut out-cut-in of ACOV to reduce wear of the pump * provide initial fluid when service is selected and pump is in Cut Out * **fitted with NRV to not allow fluid to return back to the reservoir**

Answer 21

Separator/floating piston flexible diaphragm

Answer 22

Gas inside is **Air or Nitrogen** **charged with predetermined pressure** **Gas pressure is usually greater than the pressure to operate any service ** Pump is idle: when gas is compressed and hydraulic fluid and gas pressure equalize Pump operational: when service is selected - fluid under pressure is available until pressure drops sufficiently to bring the pump on line. fluid volume is sufficient to perate a serivce once

Answer 23

permit a guaranteed number of brake applications (sufficient fluid to operate service multiple times) or stop aircraft during a rejected take off

Answer 24

* the ACOV to cut in and out too frequently. * This may cause rapid fluctuations of system pressure * Can be felt and heard as ‘hammering’ in the system.

Answer 25

**Physically attached to the service component that needs to be moved** **convert fluid flow into linear motion** * Has piston * Rod/Ram * Seals **Three types:** **Single:** powered in one direction by hydraulic power. The return movement is under string force. Used for l**ocking device** (ie landing gear downlock) **Balanced** * Piston moves in both direction * The rod is on the sides of the piston/Ram head * Equal force applied on both sides of the piston * Either sides may be connected to a mechanism * Use for N**ose wheel steering **& control boost systems **Double Unbalanced:** Piston moves in both directions Only one piston attached to the RAM used in most aircraft systems. Offers more force/resistance to be applied to extensions (ie raising landing gear) Area of the top of the piston in greater than underneath the piston * used for r**ectractable landing gear**

Answer 26

It should be noted that the area of the upper side of the piston is greater than the area of the lower side by the amount equal to the area of the piston rod; therefore the force acting on it will be greater on the larger area.

Answer 27

When fluid is trapped between the piston of the jack and a non-return/locked selector valve valve Because the fluid is incompressible and is unable to flow through the system, the piston cannot move even if a load is applied to it and is therefore locked in its position.

Answer 28

These are a form of r**otary actuator= generate rotary motion** * **needed to operate screw jacks to drive the FLAP slat mechanism** **called axial piston motor** , and are sometimes connected through gearing to operate a screw jack, or to drive generators or pumps. In some aircraft they are used for driving a hydraulic pump unit, thus enabling power to be transferred from one hydraulic system to another without transferring fluid. The construction of a hydraulic motor is generally similar to the construction of a variable volume multi-piston pump. The speed of a hydraulic motor is dependent on the flow rate of oil into it.

Answer 29

Used for **very light aircraft **that maybe only need to retract/extend landing gear powered by **DC electric motor** **Flow & valves complete the system** landing gear is in rectractable position by Hyraullic lock thermal relief valve used to relieve pressure pumps come on line when needed to restore system pressure landing gear is lowered & locked mechanically. At this point, electrical supply to the pump is switched off.

Answer 30

**Shuts off services or hydraulic supplies to specific areas. ** must be **initiated by 'external controller'** **It's not self regualting** **ex: isolate fluid in the event of engine fire**

Answer 31

shuts off flow in case of leak between upstream and downstream components. it avoids total fluid loss. It is self regulating if it sense excessive flow downstream, it will shut off and provide no operation there

Answer 32

allows 1 services to be operated by 2 supplies. if one fails, the other can replace. ex: main & emergency system main system pressure has higher pressure than emergency system pressure, therefore the valve moves and seals off the emergency supply. if main fails, the valve seals the main, and opes up the emergycy system. used for switching emergency system of landing gear and flap lowering.

Answer 33

it ensures fluid is sufficiently supplied to main controls and brakes. if system pressure drops, it closes and isolates non essentials circuits

Answer 34

reduces fluid flow to slow the operation of a service. (slowing down extension of a gear) a one-way restrictor allows full flow to one direction and slows down the flow in another

Answer 35

releases excess pressure when the 'balls unseats' due to high pressure, it allows the fluid to return to the reservoir and pressure is relieved. once relieved, the ball re-seats, consequenly closing the return to the reservoir

HYDROLICS general Flashcards

(59 cards)