Best ways to select purifier gravity disk | A Complete Guide

Why Gravity disk?

selection of gravity disk for purifier
How do I select gravity disk for Purifier?
Gravity Disk in Purifier alters the location of the oil-water interface. And further, Interface can be shifted inwards or outwards with the correct selection of the gravity disk in your purifier. And With the proper selection of the gravity disk, the efficiency of the separation can also be improved.

In a nutshell, choosing a larger gravity disk of bigger diameter causes oil flowing out of the purifier Through the water outlet, And choosing a Smaller Gravity disk may result in lesser purifying efficiency. As the outer periphery of the disk stacks are left unused.

The Gravity disc can be chosen from the set of discs that are provided by the manufacturer. Every bit is super-simplified for you and easy to remember.

With the end of this article, you can easily select a gravity disk

1. When the specific gravity of the oil at 15 ℃ is known.

2. When the specific gravity of oil at a certain temperature is known.

And must-have information on purifier (It's so easy)

Understanding Gravity Disk basics:

An important thing to keep in mind is that the diameter if the gravity disk is the innermost circle diameter and water flows it through the inside.
purifier gravity disk innercircle diameter
The Gravity Disk Diameter is the inner circle diameter. This is important.
Water Flows as shown in the figure. And directed to a stationary impeller just like oil impeller
(Note: Nobody calls this as the "impeller". its called a "pairing disk").

Sometimes there may be 2 impellers (AKA pairing disks). If you have SAMGONG purifier manual nearby have a look at page the 19.
You could see "IMPELLER 1" and "IMPELLER 2".

A discussion with My fellow mate, he said he didn't had any impeller for collecting water. he just had one impeller for taking that oil out.

How to select a good gravity disk for your purifier
PIC: Shows the cross-section of a gravity disk.

How the gravity disk actually works? how interface is maintained? Can you create this in your own backyard?

Yes. Consider an empty container

purifier gravity disk empty container
An Empty container

Now add water to the container
adding water to the container

Now stir the water and it forms a shape like this
 stir the water and till it forms a shape like this

Now take a different container shaped in this manner
Now try a different container shaped in this manner

Add water to the new beaker
Add water to the new beaker fo this shape

Now stir again you can see a shape forming like this
Now stir again, you could see a shape like this
and all the water would be thrown out.

Now you have got the air-water
Now you have a the air-water interface

to the mouth of the beaker
Attach a disk [gravity disk] to the mouth of the beaker

With reduced mouth opening than shown in the picture
Now with reduced mouth opening than shown in the picture (7/10)

The diameter of the gravity disk means the innermost circle
You can see the interface getting inside, lesser the dia of the Gravity disk, 
The interface moves further inwards

Consider our classic Example :
oil and water in a normal beaker
Oil and water in a normal beaker or in a settling tank.

Make it vertical with aided with centrifugal force
oil and  water in settling tank
Oil and water in a  Vertical beaker
if it's in a vertical position
And rotated (or applied a centrifugal force)

Fix a top Disk on it

Purifying by rotating

Approximating a Purifier model for better understanding

redirecting like purifier

These images will help you understand easily

Can you alter this interface? 

Yes. of course.
As you have seen in the above diagrams, changing the mouth diameter changes interface. And here is a little explanation of the 2 major parts if you haven't Gained it already.

purifier disk stacks with top disk
PIC: Showing Purifier Disk stacks and Top disk

Note: gravity disk dia means inner dia
(can't stress this anymore. it's that important for an easy understanding)

PIC: Purifier and Gravity disk and e-line representation. 

To gain the fullest advantage of the disk stacks, E-line should be located outside of Disk stacks.
if there are holes in the disk stacks, the e-line should be located inside the holes. (More citations needed on this one)

PIC: Showing Flow of oil in ideal Condition With the correct selection of gravity Disk

And on the other hand, If the E-line is located outside of the top disk, Oil flows out to the waterside.

What happens if my gravity disk diameter is too large?

Yes, Overflow! A larger gravity disk of bigger diameter causes oil flowing out of the purifier Through the water outlet. have this diagram for better understanding.
Purifier interface overflows
PIC: Interface moves out leads to oil overflow

Note: Water impeller section is also called a heavy liquid chamber and Oil impeller section is called a Light liquid Chamber.

purifier oil flows from the waterside
Oil flows out from the waterside. 
As the interface moves out of the top disk.

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. See the diagram for better understanding

Better efficient way for purifying
PIC: Showing a Less Efficient Way to purify

The outer periphery of the disk stacks are unused, Further leads to lesser efficiency

Gravity Disk Selection - Nomogram method

Pulled this out from google search query for you:

A diagram representing the relations between three or more variable quantities by means of a number of scales, so arranged that the value of one variable can be found by a simple geometrical construction, e.g. by drawing a straight line intersecting the other scales at the appropriate values.

Nomogram Construction: Lines and Curves

What are the 4 Lines represented in a nomogram?  (important)
1.Rising Curve
2.Falling Curve (Represented in red)
3.Horizontal line
4.vertical line

Figure 1: A simplified diagram that shows the Feed rate, temperature, and gravity disk diameter that has to be selected.
purifier nomogram showing falling curve
PIC: Showing Inside diameter, Temperature, and The feed rate

Figure 2: Added with vertical lines.
purifier nomogram with falling curve vertical line and rising curve
PIC: Purifier nomogram with Falling curve and with Vertical line
(End of Nomogram basics)

Related read: Ultra basics of Purifier and the two equations

Example 1: The specific gravity of the oil at 15°C is known

Specific gravity of oil    :  0.925 at l5°C 
Treating temperature      : 70°C
Feed rate                        :  3000 L/h 

Step 1: locate the specific gravity of oil in the extreme left line. (0.925)

Step 2: Draw a curved line along until it touches the vertical axis of 70°C [ line 1 ]

Step 3: From the 70°C line, Draw a Horizontal line until it touches 100°C line 
[ represented as bold vertical line]
Purifier horizontal and vertical line
PIC: Showing Steps 2 and 3

A zoomed image for a clear understanding. For mobile device

Purifier nomogram Zoomed image
Purifier nomogram zoomed lines 1 and 2

Step 4: Connect the right end of line 2 [horizontal - dotted - pink] and point it to
the feed scale using a straight line ( 3000 L / h )

Purifier nomogram pointing it to feed line
Purifier nomogram pointing to feed scale line from 100 C vertical line

Gravity disc inside diameter is obtained from the gravity disk diameter scale. here in our case, it's 79 mm [ as the pink bold line passes through section 79  ]

(Thanks to Samgong purifier manual. Extracted exact values from it)

Nomogram diagrams are different for different types of purifier models from the same manufacturer.

For example:

Samgong Purifier [ Model SJ20 G/GH ]
Samgong Purifier [ Model SJ30 G/GH ]
Samgong Purifier [ Model SJ50 G/GH ]

Has different charts (nomograms) for selecting a gravity disk

All the Nomogram Charts you can find it in your Purifier Manual labeled Under
"Gravity disc selection procedure"

I suggest you have a glimpse this "Nomogram" in this Wiki link and familiarize with the rarely used word: Nomogram

Related Read: Purifier - Clarifier and its difference

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

Specific gravity of  oil                : 0.944 at 50 °C 
Treating temperature                   : 98°C
Feed rate                                     :1250 L / h
purifier nomogram showing curved line
PIC: Purifier nomogram with Up curve lines 

Step 1: Follow the rising curve from the specific gravity line  0.944 till the vertical line of 50°C [line 4]
PIC: converting to a specific gravity at 15"C

[Now follow the same steps - as shown in example 1]

Step 2: Draw line 5 with the falling curve till the line of 98°C 
purifier nomogram step 2
PIC: locating in the operating temperature-  line 5

Step 3: Draw horizontal line until it touches the vertical line of 100 °C 

Purifier nomogram zoomed image no two
PIC: A zoomed Image for mobile device

Step 4: From the right end of the horizontal line draw a line pointing it to feed rate scale
1250 L/ h
purifier nomogram pointing it to feed rate scale line
PIC: Pointing to Feed Scale

Step 5: Selection of the gravity disk from the gravity disk diameter scale

Selecting gravity disk for purifier
PIC: Selecting a Great gravity Disk.

Related read: The 10 purifier overflow reasons that you can't miss.

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  1. What if you have computed a 71.5mm diameter gravity disc size and you only have 71mm and 72mm. What are you going to choose between the two? And why?

    1. You better choose the 71mm as interface moving inward is better than going outward resulting overflow.


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