Fresh water generator as name suggest is an machinery onboard which is used to generate fresh water for various purposes like drinking, washing etc. An engineer should know as how to operate this machinery effectively as water is a crucial fluid onboard.
This machinery uses the principal of evaporation of water at lesser temperature if done so in low pressure conditions. Thus we have a vacuum system in most of the FWG used on board. The jacket cooling water of main engine is used to provide the necessary energy for the evaporation. For detailed information on this please read: How Freshwater Generator Work
How to Start Fresh Water Generator
Here is the step by step approach for this and to make things easier we have given the diagram below.
1) Open following valves:
· Overboard Valve
· Ejector pump inlet and outlet valve
· Valve to bilges
2) Close Following valves:
· Air vent at the top of machine.
3) In the control panel, you will see main switch, turn it on, which will result in power supply for the FWG operating panel. Make sure that Secondary alarm is in the off position, as it will keep on sounding in the beginning, as condition are not that stable.
4) Now turn on the Ejector pump.
Diagram showing the pipe line arrangement
5) You can see slowly the vacuum developing inside the machine. We want it to be 98%, so wait for it. In site glass you can see the level of water inside the machine.
6) After it is satisfied that we have 98% vacuum, it is time to adjust the heating water that will come from the main engine jacket cooling.
7) You can see that there is a bypass arrangement provided for it on the extreme left. Right now it is in the open position, and the inlet and outlet of it to the FWG are closed. This means no water is coming to this machine.
8) Open the outlet valve first and then the inlet valve.
9) Now you will see change in the vacuum, it will decrease a little bit.
10) Slowl and steadily close the valve which is in the line to the jacket water cooler. This will result in more and more hot water being coming to the fresh water generator.
11) At this time, see in the site glass as how much water level is there. We usually don’t let is drop below the half level of the glass.
12) At the same time, keep an eye on the vacuum. When things are stable, it is time to run the distillate pump.
13) In the beginning, we will let the fresh water to go in the bilges, so as to get the stable PPM. You can see that in the controlling panel.
14) You will start seeing that PPM is dropping slowly as time passes.
15) One time will come, when it is lesser or equal to the required PPM.
Note: If the PPM is not coming down, you have to manipulate the amount of jacket cooler main valve open or close.
16) Now on the secondary alarm system with the given PPM set value.
17) Finally close the valve to bilges and open that to the fresh water tank.
18) You are generating fresh water as required.
19) Keep an eye on all the parameters for further 10 minutes.
20) You are done with the starting.
How to Stop Fresh Water Generator
1) Now we will do everything in reverse of what we did during the starting.
2) Close the valve to fresh water tanks.
3) And stop the distillate pump, followed by turning off the secondary alarm system.
4) Now slowly start opening the jacket water cooling valve. Wait for 5 minutes.
5) Now close the inlet valve to the machine first, and then the outlet valve. This is to make sure that, no water remains in the lines after shutting down.
6) You will see the water level in the sight glass will increase. Keep running the ejector pump for 15-20 minutes to cool down the plant.
7) After this stop the pump and close the inlet and outlet valve.
8) Close the overboard valve.
9) Finally open the air cent if required.
10) You are done with the stopping of the machine.
Read here: What are the Reasons for FWG Salinity Alarm?