The tube attached to the pump gradually degrades as it is used.

As the tube degrades, this results in weakened pump capabilities.
Although it depends of the frequency of use and the test reagents, assuming about 4 hours of use per day it must be replaced approximately once every 6 months.
Please see the instruction manual for information on how to replace it.

One thing to note is that the tubes for the pure water emission pump and the solvent emission pump are made of different material.
Please see the instruction manual to confirm the type of material for the tube of the pump you are using and attach the proper material.