# 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

>> Discussion is an exchange of knowledge It Make the Mariner Perfect.... Please Discuss below...

1. for diesel oil do we use bigger or smaller gravity disc

1. greater the specific gravity of liquid used for saparation smaller the size of the gravity disc.so for diesel oil we use gravity disc of larger size than hfo and lube oil.
among three liquids used to purify on board largest gravity disc will be of diesel oil then lube oil and the smallest one will be used for havy oil

2. Correct, mentioned many times in this topic, so nothing news

2. This comment has been removed by the author.

1. The above working of the "gravity disc" is opposite as described!

The smaller the hole in the disc, and if there is water in the fuel, this will go with the fuel to the daily service tank
When the hole is zero (no hole) you have a clarifier
The tendency is always use a disc with a hole as big as possible, so no fuel is going to the sludge tank, only water, if present

2. If there is more water in fuel interface will shift towards the oil side so if we use large dia disc water escapes through the oil side so its better to use the smaller size gravity disc.

3. interface outer side then , gravity disc dia big it means...oil will come to water!!!

3. Correct, but again "so large as POSSIBLE" , so that water is throwing out at the water outlet, and with a too SMALL disc is passing with the oil to the service tank.
Besides there is apossibility that in that case "MOUSSE" is formed.

4. gravity disc works on the back pressure of separated water , it limits the flow of separated water hence it holds the water inside the purifier and builds the back pressure.
if hole dia is more then more water will flow out from the purifier and oil and water interface will expand outward
and if dia is small then back pressure of the separated water is more then it will push the oil layer inward and interface of oil and water will shift inside.
if we use too small g.disc then water will start comming out from the purified oil side and that is called leaking of purifier
if g. disc is too big than oil will come through the water outlet and that is known as overflow of purifier.

1. you said it different and nice way thankz

2. this is nicest explaination

3. Small gravity disc means more internal dia or less internal dia ?

4. this is pure logic....thankyou, people dont teach like this no more anywhere

5. gravity disc works on the back pressure of separated water , it limits the flow of separated water hence it holds the water inside the purifier and builds the back pressure.
if hole dia is large then more water will flow out from the purifier and oil and water interface will expand outward
and if dia is small then back pressure of the separated water is more then it will push the oil layer inward and interface of oil and water will shift inside.
if we use too small g.disc then water will start flow out the oilside to the separated oil tank, and make a mix with the good oil, called "mousse" (chocolate color)
if g. disc is too big than oil will come through the water outlet and that is known as overflow of purifier, or "waterlock" is broken

1. thank you for your valuable inputs....

6. I am trying to separate oil with specific gravity range of .89 to .92 at around 30 degrees centigrade. What is the correct size of gravity disc I should be using?

1. i dnt think specific gravity changes for a particular oil @ costant temp,,, refer d manual 4 feed rate......

7. thumb rule
small dia regulating ring for heavy oil
large dia regulating ring for lub oil

regulating ring too wide oil discharges through water side
when regulating ring too small oil outlet contains water

8. how to know when to use a falling or a rising curve in a nomogram

1. falling curve is used for the specic gravity at 15 degree celsious
rising curve is used if you know the specific gravity at particular temperature

9. Its very simple. See the nomogram scales, density scale is increasing from bottom to top and diameter scale is decreasing from bottom to top. Hence density more gravity disc smaller.

10. Why there are holes in discs of purifier and not on clarifier disc??

1. The clarifier is attached just after the purifier in the fuel line. The main function of a purifier is to separate the dissolved water, impurities and sludge from the fuel oil, while a clarifier removes any solid foreign material that is not removed from the oil after it passes through the purifier. Thus a clarifier is kind of a back up system for purifying fuel oil. A clarifier has NO damring and so No hole!

11. I feel the chart is nomogram and not monogram

12. How much overflow of oil is normal to water side outlet? When I disconnect hose for water outlet (heavy liquid) you can see oil droplets which are muddy together with smaller droplets of water. Is this ok or I should mount smaller disc?
One more thing, at the end of separation process, when displacement water is displacing clean oil, quantitiy of displacement water that remain in bowl is specified by gravity disc or not? Other words, will more clean oil be displaced with displacement water if I use smaller gravity disc or this is specified by water solenoid valve timing?

1. 1st case
> its not easy to say correctly without checking physically even though with ur explanation it seems fine.
2nd case
> no need to change any timings according to gravity disc

2. Ok, thanks!

3. In the case you describe, the waterlock is disappearing slowly, and finally it is gone completely and all the oil is coming out of the water outlet! SO GRAVITY DISC HOLE MUST BE A LITTLE SMALLER!!

4. We are cleaning stand by purifier, in that I will put smaller size disc and check for performance.

5. Ok, let me know the result

6. We mounted smaller size in purifier. Same quantity is dripping out but now it contains more larger dropplets of watter than before. There is still some oil but less.

13. strange, i should see the situation on the spot. maybe there are other leaks such as rubber seals that need to be replaced.?

14. What does "flushing" means in purifier? And how does it done?

It is said in one of the procedures prior starting overhauled purifier that: FLUSH THE INSIDE PIPES CONNECTED TO THE PURIFIER(OIL DELIVERY, WATER SUPPLY, AND COMPRESSED AIR LINES) TO COMPLETELY REMOVE FOREIGN MATTERS TO THEM.

Im just confused on how to do this and what to use as for flushing.