Filter press operation: when should filtration be stopped during a plate-and-frame (filter press) cycle?

Introduction / Context:
Filter presses operate batchwise. Determining the proper end point of a cycle maximises throughput without wasting energy or risking cloth damage. Operators watch pressure, flow, and time trends.

Given Data / Assumptions:

• Constant-pressure or ramped-pressure filtration in a plate-and-frame press.
• Observable variables: filtrate flow rate and pressure.

Concept / Approach:
As cake builds, resistance increases, flow declines, and pressure rises. The practical end point is when filtrate flow stops or becomes negligible and/or when pressure spikes, indicating the press is “choked” by the cake or cloth blinding. Stopping then prevents excessive mechanical stress with minimal gain in recovered liquor.

Step-by-Step Solution:
Monitor dV/dt → tends to zero near end of cycle.Observe ΔP → rises sharply as channels close.Stopping upon low/no flow and sudden overpressure is recommended.

Verification / Alternative check:
Standard operating procedures specify maximum time, minimum flow, or peak pressure criteria—any of which can trigger shutdown.

Why Other Options Are Wrong:
“Cake becomes very dense” is qualitative and not a reliable, instrumented trigger on its own.

Common Pitfalls:
Overextending cycles hoping for marginal extra filtrate; this increases downtime and risks cloth fouling.

Final Answer:
both (b) & (c).