Maximum flow is a configuration rating, not your duty point
One pump family can have several flow ratings. The WILDEN PS4 metal family shows why the diaphragm configuration belongs beside the number.
A large maximum-flow number is easy to compare. It is also easy to read too much into it. Before treating that number as a specification for your installation, check which configuration it describes.
One family, three published maxima
For the WILDEN PS4 clamped metal family, the manufacturer lists 310 L/min with rubber diaphragms, 314 L/min with EZ-Install TPE and 375 L/min with Full-Stroke PTFE. These are separate configuration ratings. The 375 L/min figure should not be attached to every PS4 metal pump.
The illustration compares these published maximum values. It is not a performance curve and does not describe air consumption or flow at a specified discharge pressure.
Compare the requirement, then the configuration
For a purchasing comparison, create two columns: what your process needs and what the proposed configuration can deliver under those conditions. Put the diaphragm type, fluid properties and available air supply beside the flow requirement. If a quotation omits the complete configuration, ask for it before comparing the offer.
Keep maximum pressure separate
Do not assume the maximum flow and maximum working pressure can be achieved at the same time. Ask for the applicable performance curve and identify the operating point. The table on a product page is a useful summary; it is not the complete operating envelope.
When reviewing a replacement, retain the old full model code and the new proposed code. This makes configuration differences visible before the order is placed.