Question

Which of the following statement(s) holds correct for a screw press?

(A) Compression ratio is the ratio of the volume displaced per revolution at feed end to that at discharge end.

(B) Volume displaced at feed end is considerably less than at discharge end.

(C) Volume displaced at feed end is considerably greater than at discharge end.

(D) Volume displaced at feed end is equal to that at discharge end.

Choose the correct answer from the options given below:

• (A) and (B) only
• (A) and (C) only
• (D) only
• (A) and (D) only

Hint:

Think about how the flight volume of a screw press changes from the feed end to the discharge end, and what that change is called.

Answer 1

The Correct Option is B

Step 1: A screw press (expeller) has a rotating worm shaft running inside a stationary cage. The root diameter of the shaft increases and the flight pitch decreases as you move from the feed end to the discharge end.

Step 2: Because of this changing geometry, the free volume available for the material inside one flight space keeps shrinking as the material travels from the feed end to the discharge end. This shrinking volume is what squeezes the oil out of the seed and builds up pressure.

Step 3: The compression ratio of a screw press is defined exactly as statement (A) says, the volume displaced per revolution at the feed end divided by the volume displaced per revolution at the discharge end. This ratio is always greater than 1, which only makes sense if the feed end volume is considerably larger than the discharge end volume. That confirms statement (C).

Step 4: Statement (B) says the opposite of what actually happens, so it is wrong. Statement (D) claims the two volumes are equal, but equal volumes would mean zero compression and no oil expression at all, so it is also wrong.

Step 5: Only (A) and (C) are correct, so option 2 is the answer.