Fresh Water

Question 1

What are the uses for fresh water?

Answer 1

Drinking
Washing
Cooking
Cleaning

Question 2

What services are provided by the fresh water system?

Answer 2

Laundry 
Galley
Showers and sinks
Water heaters 
Medical use
Bridge window washers
Fresh water hose reals 
Machinery cooling

Question 3

What is osmosis?

Answer 3

The transfer of pure water through a semi-permeable membrane into salt water.

Question 4

What is reverse osmosis?

Answer 4

The transfer of water from salt water through a semi-permeable membrane into pure water.

Question 5

What is TDS and what does it mean?

Answer 5

Total dissolved solids.

The measure of water purity.

Question 6

What is the TDS of sea water?

Answer 6

34,000 ppm

Question 7

What is the TDS of water after desalinisation?

Answer 7

250 - 300 ppm

Question 8

How much of the sea water is ejected?

Answer 8

80%

Question 9

What is desalintised water known as?

Answer 9

Permeate

Made water

Question 10

What is the waste water called after desalination?

Answer 10

Concentrate

Question 11

What are the two filtration stages of a reverse osmosis plant and what level do they filter the water to?

Answer 11

Stage 1 - bag filter - filters to 60 microns

Stage 2 - two cartridge filters - 10 microns

Question 12

What pump does a reverse osmosis plant use and what pressure does it provide?

Answer 12

High pressure, 3 piston positive displacement pump.

Provides pressure up to 65 bar.

Question 13

What is the purpose of the cushion membranes?

Answer 13

To separate remaining salt water and waste from the made fresh water.

Question 14

What is a CCV and what does it do?

Answer 14

Concentration control valve.
Controls the back pressure of the sea water acting on the membranes. When valve is closed, back pressure is increased and the amount of permeate is increased. When valve is open, back pressure is decreased and the amount of permeate is reduced.

Question 15

What does the anti-scalant dosing unit do?

Answer 15

Prevents precipitation of calcium salts forming on the membrane surfaces.

Question 16

What is the purpose of the accumulator?

Answer 16

To protect the pump.

Question 17

What anti-scalant is used and at what rate is it added?

Answer 17

Hypersperse (anti-scalant) is added at a rate of 5 ppm.

Question 18

What is added to the water after it has passed through the membranes and why?

Answer 18

Chlorine, added after the membranes as it can damage the membranes. Used to kill off harmful bacteria.

Question 19

When are chlorine levels checked and what level are they kept at?

Answer 19

Checked daily and before embarkation. Levels kept at 0.2ppm.

Question 20

When should desalination not be carried out?

Answer 20

When the source of water is likely to be contaminated. Ie harbour water, estuary water.

Question 21

What three tests are carried out on fresh water?

Answer 21

CHEMets (turns pink, dark = more chlorine)
Visual (looks clean and free of debris/particulates)
Taste (carried out last, shouldn’t take overly chemically)

Question 22

What is used to heat water on ship?

Answer 22

Calorifier

Question 23

What colour are fresh water hoses and what must be done before using them?

Answer 23

Blue in colour.

They should be flushed with fresh water before use.

Question 24

What happens when air moves through a fresh water system?

Answer 24

‘Water hammer’

A loud, repetitive banging noise in the pipes.

Question 25

What is used to eliminate ‘water hammer’?

Answer 25

Air eliminator.

An auto bleed valve at high points in the system.