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

A screw press works by forcing material through a shrinking space. From the feed end to the discharge end, the shaft's root diameter grows and the pitch of the flights gets smaller, so the volume trapped in each flight keeps getting smaller.

Compression ratio is simply how many times smaller the discharge volume is compared to the feed volume, written as (volume per revolution at feed) divided by (volume per revolution at discharge). Since compression must happen for oil to be pressed out, this ratio has to be well above 1, which directly means the feed end volume is much bigger than the discharge end volume.

So statement (A), the definition, and statement (C), the physical description of what that definition implies, are both correct, while (B) and (D) contradict how a screw press actually squeezes material.

\[\text{Compression ratio} = \frac{V_{feed}}{V_{discharge}} \gt 1 \Rightarrow V_{feed} \gt V_{discharge}\]

\[\boxed{\text{Option 2: (A) and (C) only}}\]