What is Gravity Disc Of Purifier? Selection and fuctions of Purifier Gravity Disc

Gravity Disc or Dam Ring
            Purifiers have great role in marine ships.A ring fitted at the top of disc stack from where water is passing out is called gravity disc.Oil which is for purification may not be of same type it is of different densities or viscosity, so the interface change. To create the correct interface between water and oil it is very important to select correct gravity disc size

Functions of Gravity Disc
>Gravity disc in purifier is the one which controls the output of the quality of the fuel.
>Dam ring is responsible for creating the interface between the oil and water
>Back pressure is maintain by gravity disc

Must Read:> Alarms And Shut Downs (Safeties) in Purifier 

Purifier Gravity Disc Size Selection
>Selection of gravity disc is depends on Specific Gravity,Temperature and feed rate
>There are 2 method to find the correct size of Dam ring
             1.Using Monogram
             2.By trial and Error method

             1.Using Nomogram

             To find the correct gravity disc monograms are using on board ship here it is given an example of monogram graph

Method Of Using Nomogram

    For better understanding we can explain with the help of an example 

• ‹ Specific gravity of treated oil 0.925 at15℃ 
• Treating temperature 70℃ 
•  Feed rate 3000 L/h 

Selection method 
>From an intersection between falling curve I of specific gravity of 0.925 and the vertical line of 70℃, draw horizontal line II to reach the vertical line of 100℃. 
>Connect between the right end of line II and the point of 3000 L/h on the treating capacity scale using straight line III. 
>Read within which section of gravity disc Inside diameter scale the intersection made by line III falls. 
>For this select a gravity disc having an Inside diameter of φ79. 

     

             2.By trial and Error method
                        In this method use different Size of gravity disc use one by one and check the water and oil side for any leakage of oil in water side and water in oil side. If one particular gravity disc suits ie, no water in oil side and no water in water side which can be considered as a perfect one. 

What will happen if we use big Diameter/smaller gravity disc

              Bigger the diameter of the disc, the possibility of having water mix with fuel is high while if the diameter of the disc is smaller then the more good fuel you get.If we are to use so small diameter disc, this will cause some good fuel oil to be thrown to the sludge tank.There is also a drawback if you use to much large diameter disc because there is a possibility that the water will be mixed with fuel.So it is very important that the size graity disc should be correct.

  If you know more about gravity disc discuss below.

Reference 
Pics are from SAMGONG-MITSUBISHI Manual