LP & HP Air Flashcards
HPAC performance trial
- Carried out every 6 months
- Monitors performance of compressor
- time trail based on compressor output
- Compressor delivers 115 m’3/hr at inlet temp at 10’c
- System is configured to fill one 258 clinder from empty to 276bar
- Time required is 32min - deviation indicates problems and requires investigation
Brief description of separators fitted to a HP air compressor
- After compression stage
- Causes moisture droplets carried in the air, to fall out of suspension
- Bottles with inlet pipe extended some way into the bottle
- As the air changes direction, water falls to the bottom and is drained when the valve opens
Stage 1 of the filter driers
- Removes bulk liquid contamination
- Uses high efficiency vortex operation water separator
- Removes 90% condensate and aerosol contamination at 21’c and 80% particle removal (10micron and above)
- fitted with an automatic drain that will discharge for 3sec every 20min depending on the drain mode selected
Describe the 3 operating modes of a HP drier
Pos 0 - Heatless mode -
- Heater circuit is disabled
- same as pos1 but cycle time is reduced to 40 min(20 min on each column)
Pos 1 - heat regenaive mode
- preferred operating mode
- equipment is fully automatic with the outlet solenoid valve, hygrometer sensor
- total cycle time is 2hr40min (1hr20min each column)
Pos 2 - bypass mode
- used for maintenance/emergency conditions
- mode disables the dryer control circuits
- still maintains operation of the inlet filter solenoid drain valves
Daily checks on LP air drier
- Check all gaskets, control valve, pipes and fittings for air leaks
- Ensure changeover of the desiccant columns occur approx every 2 min
- Manually operate the pre-filter and after filter drains. Check drains are clear
- Ensure that the on-line column pressure gauge reads between 7&8bar
- Ensure that the off-line column pressure gauge reads 0bar
- Ensure moisture indicator crystal are blue (normal)
- Check dew point reading on hygrometer. Should be -40’c min
5 faults that affect compression
- Blocked filters - prevents air entering compressor
- Leaks - air leaks on connections, joints and valves will reduce output
- Worn piston rings/cylinder liners - wear will result in loss of compression
- Faulty cylinder valves - air will leak past, compression is lost
- Poor cooling - causes cyclinders to become hot, prevents full charge
List and describe the 4 functions of the oil system
Lubrication
- Fed into moving parts
Cooling oil
- Injected into rotating assembly is in direct contact with air.
- Absorbs heat from air which is then dissipated through oil cooler
Sealing
- Helps to seal any gaps around vanes, this maintained partial vacuum and HP within cycle
Control
- Fluctuations in oil pressure is used to control the unloading device
- Varies its output as demand requires
Describe how oil is removed from the discharged air
Oil baffle plate
- Fitted to outside of stator
- Heavies oil strikes baffle plates and drops back to bottom of casing
- Removes 99% of oil
Coalesces filter
- air passes through the filter removing remaining oil down to 5ppm
- Then returns to the casing via the oil return valve
Describe the minimum pressure outlet valve
- Similar to a pressure maintain valve
- Ensures that enough pressure is maintained within the compressor to circulate oil
- Acts as a non return valve, when compressor is shut
What safety devices are fitted (ref LP pump)
Pressure relive valve
- fitted in compressor discharge line before outlet valve
- Relives at (8.5-10bar)
Oil temp trip
- interlock fitted in starter if oil temp exceeds 104’c
Air temp protection
- Unloads if air discharge temp exceeds 125’c
Safety when working on LP system
- Stop the compressor and isolate from supply
- Close the air outlet valve to isolate from air system
- Open relevant drain valve to vent pressure from the air cooler and pipe work
- Check end pressure indicator reads 0
- TAG OUT routine
What precautions should be observed with the oil filler plug is being removed
- Dont remove plug until all air pressure has drained
- Stop and allow pressure to dissipate
How to clean or renew an air filter
Stop and islolate supply
Unscrew handwheel and remove filter and seal cover
Remove air filter element
Replace with new or Vacuum/blow dust from filter
Wipe clean filter support and inside of filter cover
Replace filter
Replace filter cover and seal, secure assembly with handwheel
List the content of the pressure vessel register
Part one
-compresses gas pressure vessel register (cylinders and receivers)
Part two
- accumulators and miscellaneous pressure vessel register (hydraulic accumulators, filters, dryers and separators)
Part three
- relief valve register
Part four
- fixed fire fighting system cylinders register
Explain the pressure vessel register
Legislation requires a record of all testing is maintained by the user
To be maintained by all ships and subs to record the identification, test details and test perioditices of all non-transportable compressed air and nitrogen cylinders, receivers, filters, dryers, sepeartors, relief valve and hydraulic accumulators and field fire fighting cylinders
