HomeMarine Auxiliary MachineryMarine PurifierHow to Select Gravity Disc for Purifier? Size of Gravity Disc

How to Select Gravity Disc for Purifier? Size of Gravity Disc

Selection of correct size of gravity disc is very important to obtain optimum cleaning of oil according to the density of the medium to be treated and throughput.

The diameter if the gravity disk is the innermost circle diameter and water flows it through the inside.

What will happen if the size of gravity disc is large?

The oil will overflow. A larger gravity disk of bigger diameter causes oil flowing out of the purifier Through the water outlet. This is because the interface will shift outside as the pressure will decrease from water outlet side.

What if Gravity disk is small?

Smaller Gravity disk may result in lesser purifying efficiency as the outer periphery of the disk stacks is left unused. Also there may be chances of water going out with oil from the oil outlet of purifier

How to select the correct size of gravity disc of purifier on ship?

A correct size of gravity disc is selected based on the specific density of oil, feed rate and purification temperature with the help of Nomogram diagram. It is a diagram that shows the Feed rate, temperature, and gravity disk diameter that has to be selected.

Nomogram diagrams are different for different types of purifier models from the same manufacturer. They given in the purifier manual

Purifier Nomogram Showing falling curve

To Find the correct size of Gravity disc, you must know either specific gravity of treated oil at 15℃ or specific gravity of treated oil at a certain temperature is known

Case 1: Specific gravity of treated oil at 15℃.

  • Specific gravity of treated oil: 0.944 at 50℃
  • Treating temperature: 98℃
  • Feed rate: 1250 L/h
  1. Find the intersection between the falling curve of your specific gravity and the vertical line of your treating temperature.
  2. Draw a horizontal line from that intersection to reach the vertical line of 100℃.
  3. Connect the right end of that line with the point of your feed rate on the treating capacity scale using a straight line.
  4. Read within which section of the gravity disc inside diameter scale the intersection made by that line falls.
  5. Select a gravity disc having that inside diameter.

For example, if your specific gravity is 0.925 at 15℃, your treating temperature is 70℃, and your feed rate is 3000 L/h, then you can use the nomogram to find that you need a gravity disc with an inside diameter of φ79

Case 2: The specific gravity of treated oil at a certain temperature is known.

Azlan Ahmad Salmani
Azlan Ahmad Salmanihttp://BrightMariner.com
Marine Engineer | Fleet Management Ltd | MERI Mumbai


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