Centrifugal Seperators Page 35-36

Question 1

What is the function of the gravity disc in centrifugal purifiers?

Answer 1

They determine the free water level within the bowl and position of the oil water interface.

Question 2

What are the consequences of fitting too large a gravity disc?

Answer 2

1. Water carries over with the fuel
2. Loss in water oil interface seal
3. Seal interface near to bowl edge

Question 3

What are the consequences of fitting too small a gravity disc?

Answer 3

1. Slow oil purification rate
2. Solid matter carries over
3. Poor sludge removal

Question 4

What are two factors that influence the separating process?

Answer 4

1. Input temperature of the oil to be purified
2. The density of the oil which is to be purified

Question 5

What are two reasons for a purifier not attaining full running speed?

Answer 5

1. Fouled, dirty, heavy sludge deposits on the purifier bowl
2. Driving motor, bearings worn, under-performance

Question 6

What is the function of a purifier?

Answer 6

To remove solid particulate and water from the fuel.

Question 7

What is the function of a clarifier?

Answer 7

To remove solid particulate only.

Question 8

What are two constructional differences between purifiers and clarifiers?

Answer 8

1. No gravity disc in clarifiers, as there is no oil water interface to maintain inside.
2. Larger discs and bowl size than purifiers for a longer dwell time.

Question 9

Outline the separation process that occurs within centrifugal oil purifiers.

Answer 9

Centrifuging amplifies the effect of gravity separation and makes the process much quicker. A small amount of water is added to prime the machine. High speed rotation forces impurities to the outside of the bowl, leaving clearer oil in the center. A disc stack enlarges the bowl’s surface area. Clean oil is pumped out, and a gravity disc controls the water interface to prevent cross contamination. The purifier periodically de-sludges to discharge collected solids.

Question 10

What change is required to the purifier for an oil of lower density?

Answer 10

A smaller gravity disc will be needed to maintain the oil water interface. If not changed, oil could be lost in the water outlet.

Question 11

Q4a) Outline the separation process that occurs within centrifugal oil purifiers (12)

Answer 11

1. Centrifuging amplifies the effect of gravity separation and makes the process much quicker, this is due to using the force of
   gravity to separate particles and water due to them having different densities
2. 3. A small amount of water is added to purifier to prime the machine and prevent the oil carrying over to the water outlet
      When oil is inside the bowl, the high speed rotation causes impurities to be forced to the outside of the bowl leaving the more
      clearer oil in the centre
3. 5. 6. 7. Separation is aided by the addition of a disc stack which enlarges the bowls surface area
            After this the clean oil is pumped out
            Within the oil outlet there is a gravity disc that controls water interface than helps prevent cross contamination
            Periodically the purifier will de-sludge to discharge the solids that are collected in the bowl

Question 12

4B Describe the change required to the purifier if it is to be used for an oil of lower density (4)

Answer 12

For fuel of a lower density, a smaller gravity disc will be needed in order to maintain the oil water interface. If the
gravity disc wasn’t changed oil would be lost in the water outlet, which could drain a sump, fill the bilge sludge tank
or even cause damage to a machine

Question 13

Q5 With reference to a centrifugal oil separator:
a. b. Explain the importance of using the correct size of ‘gravity disc’ (12)

Answer 13

Too large a gravity disc will cause,
The oil water interface becoming too close to the bowl periphery
The liquid seal will be broken and oil may through the water outlet

Too small a gravity disc will cause,
The oil water interface becoming too close to the bowl centre
The water in this case may pass up through the oil holes, through the oil outlet contaminating the
oil.

Question 14

State the two factors that determine the size of the gravity disc to be used (4)

Answer 14

Change to the purifier throughput rate, requiring a change in back pressure
Change in the input temperature of the medium to be processed