Test 1 2.0 Flashcards
State 8 uses of hydraulics in the RN
- steering gear stabilizers
- cpp
- Davits and cranes
- winches, capstans, windlass
- stores lifts, aircraft lifts, weapons lifts
- watertight doors, hanger door, hatches
- periscopes, masts, aircraft systems
List 3 base type hydraulic fluids used in the RN
Water based
Synthetic fluid
Petroleum oil
Definition of viscosity
Viscosity: measure of fluid’s resistance to flow, measured in centistokes
Name 3 types of methods defining viscosity
Methods of defining:
- absolute viscosity: force needed by fluid to overcome its own friction
- kinematic viscosity: fluids internal resistance to flow under gravity
- SUS (relative viscosity): time in seconds for 60 ml oil to flow through orifice at a given temp.
- SAE number: oils resistance to thinning at high temps.
List 4 types of pumps used in hydraulic power systems
- gear pumps
- screw pumps
- q pumps
- vane pumps
- radial piston
- centrifugal
List types of rotary actuators
- gear
- vane
- piston
Describe the operation of the meter-in volume control valve
- flow control valve placed between pump and actuator, controlling fluid going to actuator.
- excess returned to tank/ reservoir
- used where load continually resists movement of the actuator
- used when moving vertical cylinder under load, or pushing load at controlled speed
Occasions when flushing of a hydraulic system is to be carried out
- after installing pipework
- after major repairs or refits on system
- after opening system in service when particulate contamination has or may have been introduced
- any occasion when sampling indicates particulate contamination level above certain level
In a ships stabilizer control system What are six inputs to the control panel
- roll angle
- roll velocity
- roll acceleration
- natural list
- fin feedback
- forced roll
Limitations that apply when steering the ship after an electrical power failure
When using hand pump to steer:
- above 10 knots: 5 degrees
- below 10 knots: 10 degrees
- Response to helm orders will be slow.
- manoeuvring kept to a minimum
- operating close to another vessel not recommended
Advantage/ disadvantages of using hydraulics over electrical motors
Advantages:
- reliable
- simple, easy to understand
- easily reversed
- no spark risk
- infinite speed range
Disadvantages:
- noise
- less efficient
- fire risk on mineral oil systems
- risk of contamination
functions we require from hydraulic fluid ( ex. Lubrication)
- lubrication (internal lubrication of moving parts)
- sealing (fluid often only seal against pressure in component)
- cooling (circulating oil through cooler dissipates heat)
- cleaning (circulating oil through filters removes particulates) LSCC
List the reqs of the ideal hydraulic fluid
- stable
- incompressible
- lubricating
- non toxic
- non flammable
- low viscosity
List where the following hydraulic fluids are used in the RN : OX 30, Ox40, houghto-safe 620, rust veto NTP 32
ox 30 :
- mineral oil with additives, red in colour, able to absorb 40% of water and maintain system requirements .
- flushing oil with water contamination.
OX 40:
- typically 40% water/ 60% poly glycol mix.
- contains additives to improve fluid life, component wear characteristics, provide sea water capability.
HS620:
- type 45s stabilizers, steering, and davits
- excellent lubrication
- fire resistant
Rv NTP 32 :
- mineral oil based preservative developed specifically for use with OX40 systems
Types of accumulators used in hydraulic systems and their purpose
- Weight loaded piston: constant pressure regardless of fluid level.
- Spring loaded piston: faster response than weight loaded type
- Gas loaded piston: capable of high flow rates in which pressure varied with gas compression
- Gas loaded bladder: has lower inertia, more suitable for smoothing out pressure fluctuations
