Do you mean to say you tested the pumps attached to the L298 board and controlled them using the digital inputs to that board?
Either by a simple sketch, or by directly connecting the pins to 5 volts and ground where such code might have been writing HIGH or LOW?
The L298 reduces the voltage to the motors somewhat severely, measure the voltage at the motors with your current circuit and maybe see an explanation surprise.
There are 21st century motor drivers. Or you might already be using a high enough voltage on the L298 board so the loss is not the issue.
a7