Compressors

Question 1

Checks on compressor

Answer 1

Check lube oil and CW level, check drains, check line, air filters, oil filters
Check air receiver pressure (25-30 bar), drain moisture. If there is oil it could be a leak from the scraping rings of the piston pushing oil into the air chamber.

Question 2

Starting air compressor procedure

Answer 2

1. Line up delivery valves.
2. Open cooling water.
3. Check oil level.
4. Bar over (if maintained).
5. Open manual drains.
6. Start compressor.
7. Verify water/oil pressure.
8. Verify unloader closes & close drains.

Question 3

Compressor and start air system safeties

Answer 3

COMPRESSOR
Safety valve on discharge line (~30bar)
Relief valves at both stages (5-10% above 7 & 30 bar)
High temp trip or Fusible Plug (FP more so on emergency air comp) (lifts @ ~120 degrees) (indication of fouled 2nd stage)
NR discharge valve
Unloader takes load off motor during startup and expels any condensate from the cylinders
Bursting disc is on the CW incase air gets into system due to a leak in the intercooler pipes
Drain v/vs
Low LO pressure
Pressure gauge

RECEIVER
Safety valve
Fusible plug
Manual & automatic drain v/v
Pressure gauge

START AIR LINE
Copper gauze flame arrestor

Question 4

How can oil get into the air receiver?

Answer 4

Worn piston rings

Question 5

Compressor types

Answer 5

Start air = multi-stage reciprocating piston (2 stage - 7 & 30 bar)
General service = rotary screw type

Start air compressor
Working air compressor
Emergency air compressor
BA compressor

Question 6

How many charges must a start air receiver hold?

Answer 6

6 charges
12 charges for reversible engines

Question 7

What do you do if there is low pressure in the control air system

Answer 7

Open the cross-connection pressure reduction valve to supply start air to the control air system

Question 8

How would you notice a loss in efficiency of the compressor?

Answer 8

Running hours increase caused by NR v/v or air outlet/inlet leaking or leak in cooler.

To test the performance, empty a receiver to 20 bar and time how long it takes the compressor to fill up this receiver to 30 bar (compare timings with manufacturer’s manual)

Question 9

Why do we not want water in a receiver?

Answer 9

Can cause corrosion and that can decrease the structural integrity of the receiver.
Water in the receiver is unlikely to pass to the engine due to the way it is constructed.