Pump inlet and outlet fluid port diameters vary based on the flow rate required. Inlet and outlet hose sizes must match the pump’s size. A primary concern is the risk of cavitation, which can increase repairs and maintenance costs. Changing tubing and piping size after installation is relatively fast. Knowing the correct size at installation eliminates the time and effort required to make a modification later.
For example, if a 1-inch pump has a half-inch inlet hose connected, the pump will not be able to operate at full capacity without the risk of cavitation. This risk increases dramatically as the desired fluid viscosity rises. In this example, the 1-inch pump should have a 1-inch inlet and outlet hose attached to prevent cavitation.
It is also recommended that an AODD pump be installed with a flexible inlet/outlet connection rather than being hard plumbed. As pump speed increases, vibration increases, which elevates the risk of loosening a hard plumb connection, creating the potential for leakage.
Credit by Michael Sandlin
https://www.pumpsandsystems.com/pumps/october-2016-5-minute-fix-troubleshoot-diaphragm-pump