Purifier

What do you understand by term Purifier?

As the term itself suggest Purifier is an instrument or equipment that purifies something. Now-a-days due to increase of pollutant in air our air is becoming polluted, and to counter the problem of air pollution, few cities are installing Air Purifier, home are also buying small air purifier for domestic purpose. Thus it make it clear that purifier is any equipment with the sole purpose of purifying or cleaning the given media.

Purifier is also termed as Centrifuge, as onboard the vessel, purifier use centrifugal force to separate the two medium.
A purfier consist of a electric motor which drive the various component, such as Bowl, Nodge (rotating counter), Tachometer, Gear pump(via pinion gear)

Image Credit : Arpit (SD)

To start the revolution of Bowl, it is necessary that Friction clutch(Friction coupling or Centrifugal coupling) get engage with the Drum.
Centrifugal coupling
1)Provided as a safeguard againts the starting current, because if there is solid coupling, then due to starting the large current will flow through the winding of the motor to rotate the bowl, so friction coupling allow for some time, and after certain R.P.M is being achieved by the motor the coupling get engaged
2)Every 24 hours Purifier is stopped and cleaned up, so while boxing up if something goes wrong the extent of damage because of use of friction coupling will be of lesser extent while solid coupling damage extent will be more

Electric motor via friction coupling drive the horizontal shaft, which in turn drive vertical shaft on which bowl is mounted. (via Big Worm Gear as shown in diagram).

Shear Pin Function: 

Credit : Arpit Singh

In the above diagram the big black dot on the pinion gear is the hole for shear pin in which shear pin goes, so whenever any obstruction comes in the gear pump(which transfer Oil) due to small clearance between the teeth of the gear pump and the casing of the gear pump(clearance is in Thous) the shear pins break and pinion gear comes off the shaft, because the pinion gear is mounted is R.H.T right hand threaded(and shaft rotate left hand). So when the shear pin break, due to stiffness of rotation of gear pump the pinion gear comes off the shaft and drop into the (Yellow section) bracket. Hence preventing the damage.

Working of Purifier:

The dirty oil is supplied to the center from the settling tank, and due to centrifugal force the separation between oil and water because of their different density. Water being heavier than oil is thrown out toward the wall of the bowl whereas the oil is positioned in center. Water is applied first, because if oil is supplied directly to the purifier, it will come out from the water side, so water is supplied first and it is checked that it is coming from the waterside, gradually the seal water is shut off. If we supply seal water quickly, it may come to the oil side. An interference line is formed between Water and oil, this line is also known as E-line. The position of this interface within the purifier is very important for correct operation, this interface is achieved by gravity disk at the outlet. A number of gravity disc is provided with the purifier. This Gravity disk (a.k.a Regulating Ring) that is used has different diameter for different density of oil to be purified, so if oil is being change the gravity disk has to be changed. As a thumb rule, large diameter gravity disk which does not break the seal should be used. Blind disc is at the top disc stack.

©ShipDiggers

What is Clarification:

Cleaning of dirty oil, which contain small amount of water or no water at all along with the ample amount of solid impurities, which collect at the bowl periphery. For clarifying process no gravity disk is needed, that is, a Clarifier has only one outlet at is subjected to maximum centrifugal force. Blind disc is at bottom.

Disc Stack

Purifier and clarifier bowls has conical disc stack, which maybe numbered from 150 to 200 and are seprated from each other by a small gap. Small holes are provided on these disc stack where the interference line is formed and separation take place. The centrifugal force cause oil to move inward and water and solid particle to move outward.

Centrifuge is perfectly dynamically balanced piece of equipment with very high R.P.M, so the care should be taken while dismantling and boxing it up and also during maintenance.