Fresh Water Flashcards
What are the uses for fresh water?
Drinking
Washing
Cooking
Cleaning
What services are provided by the fresh water system?
Laundry Galley Showers and sinks Water heaters Medical use Bridge window washers Fresh water hose reals Machinery cooling
What is osmosis?
The transfer of pure water through a semi-permeable membrane into salt water.
What is reverse osmosis?
The transfer of water from salt water through a semi-permeable membrane into pure water.
What is TDS and what does it mean?
Total dissolved solids.
The measure of water purity.
What is the TDS of sea water?
34,000 ppm
What is the TDS of water after desalinisation?
250 - 300 ppm
How much of the sea water is ejected?
80%
What is desalintised water known as?
Permeate
Made water
What is the waste water called after desalination?
Concentrate
What are the two filtration stages of a reverse osmosis plant and what level do they filter the water to?
Stage 1 - bag filter - filters to 60 microns
Stage 2 - two cartridge filters - 10 microns
What pump does a reverse osmosis plant use and what pressure does it provide?
High pressure, 3 piston positive displacement pump.
Provides pressure up to 65 bar.
What is the purpose of the cushion membranes?
To separate remaining salt water and waste from the made fresh water.
What is a CCV and what does it do?
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.
What does the anti-scalant dosing unit do?
Prevents precipitation of calcium salts forming on the membrane surfaces.
What is the purpose of the accumulator?
To protect the pump.
What anti-scalant is used and at what rate is it added?
Hypersperse (anti-scalant) is added at a rate of 5 ppm.
What is added to the water after it has passed through the membranes and why?
Chlorine, added after the membranes as it can damage the membranes. Used to kill off harmful bacteria.
When are chlorine levels checked and what level are they kept at?
Checked daily and before embarkation. Levels kept at 0.2ppm.
When should desalination not be carried out?
When the source of water is likely to be contaminated. Ie harbour water, estuary water.
What three tests are carried out on fresh water?
CHEMets (turns pink, dark = more chlorine)
Visual (looks clean and free of debris/particulates)
Taste (carried out last, shouldn’t take overly chemically)
What is used to heat water on ship?
Calorifier
What colour are fresh water hoses and what must be done before using them?
Blue in colour.
They should be flushed with fresh water before use.
What happens when air moves through a fresh water system?
‘Water hammer’
A loud, repetitive banging noise in the pipes.
What is used to eliminate ‘water hammer’?
Air eliminator.
An auto bleed valve at high points in the system.
