Test 1 Flashcards
Describe the two main dangers associated with high pressure air systems?
Dieseling: rapid increase of pressure causes equally rapid increase in temperature which can result in ignition of oil in compressor or ringmain.
Embolism: air at extreme pressure can pass through skin and to blood stream resulting in paralysis or death.
List the routine to be carried out to safely isolate a high pressure air system?
- Min. Two valves in supply must be closed.
- Sys. downstream of isolations to be drained.
- Iso. valves checked for leakage.
- Valve covers to be used; proper tag out, rip out procedures followed.
- Deviation from this reported to MEO.
Give a brief description of relief valves fitted to HP air equipment?
RVs: spring loaded valves loaded to shut position. When force exceeds spring tension valve opens, relieving pressure to atmosphere.
- Commonly fitted to compressor discharge, storage reservoirs, etc.
- operate at 10% above normal pressure.
Describe a breathing apparatus charging panel
two stage filter. Consists of:
- water separator with manual drain.
- filter pack with sponge for oil.
- water removal with two stage desiccant.
- odours, chemicals with charcoal filter.
- particulate by sintered bronze filter.
What is the purpose of compressed air systems?
Provide storage and transfer of energy in form of compressed air
List and briefly describe advantage of air systems
- Readily available supply - reliable source
- Flexibility of use - variety of applications
- Easy storage- storage of large quantities of
- Easy transfer - through small pipes
- Low fire risk - non combustible medium.
Give a description of the main and dedicated storage bottles fitted to HP air system
Main storage:
- increase capacity of system and fluctuate with system pressure
- provide reserve of stored energy, allows ship to recover from total electrical failure.
- maintain system pressure when compressor shut down, decreasing start and stops.
Dedicated storage:
- directly connected to individual equipment
- connected to ring main but with non return valve in supply line
- do not fluctuate with system pressure. Remain full. Further reserve in event of complete system failure
Give a description of the pressure vessel register
- Used to record identification, test details, and test periodicities of all non transportable compressed air and nitrogen cylinders, receivers, filters, dryers, etc.
- responsibility of MEO to ensure equipment in PVR is maintained and is up to date.
Give a description of how HP air cylinders are maintained in ships
- bottles, cylinders, and receivers stamped with unique serial number, last test date and start life date
- ID numbers and test date recorded in PVR
- drain valves must be correctly positioned at the bottom so water can be drained
- bottles must be drained using drain valves in accordance with instructions
- start life date triggers following maintenance
- deviation only permitted with external verification
- inspection done only by external agencies
Description of air dryers
- dryers fitted to outpost of compressors to remove contamination
Consist of:
- pre filter pack
- columns
- after filter pack
Briefly describe types of compressors and give examples of typical applications of each
Two types: positive displacement, dynamic displacement
Dynamic displacement:
- fan type arrangements moving large quantities of air at low pressure.
Positive displacement:
- rotary compressors suited to LP systems
- reciprocating compressors produce HP air
Describe operation of concentric plate valve
- operates on 2 stroke cycle, involving 3 processes.
Inlet:
- as piston travels down, pressure drops. High pressure from atmosphere exerts force on inlet plate valve forcing it open allowing air to enter.
Compression:
- piston rises, volume in chamber decreases, pressure increases
Exhaust:
- pressure in cylinder rises exerts force on discharge valve, compressed air leaves cylinder.
List and describe the factors that effect the efficiency of an HP air compressor
- air filters (blocked/ dirty)
- leaks (leaks from valves, pipe connections, or joints)
- operation of cylinder valves (valves not seated correctly)
- cooling arrangements (lack of cooling causes walls to be hot)
- worn piston rings
Describe pressure maintaining valves fitted to HP air compressor
Designed to remain closed until compressor reaches working pressure. Either dome loaded or spring loaded type.
Describe the basic construction of a hydrovane LP air compressor
- fixed cylindrical stator housing eccentrically mounted rotor.
- eight slots fitted with cast iron vanes
- vanes free to slide in and out.
