Replacement diaphragm for the rena air pumps 100 200 300 amp 400 the diaphragm on an air pump is a constantly moving part and can over time tear or split air pumps with a damaged diaphram may produce a low amount of air or non at all replacing the diaphragm is a simple procedure and only requires a screwdriver to open the air pump unit in order to access inspect and replace the diaphragm within