The Farm Pump
When the pump is not in use the tube with water deflates slowly because the piston and de foot valve aren’t entirely watertight. If the tube is empty, it won’t start up again just because the piston moves back and forth in air. This can be solved by filling the pump with water from above. Once the piston reach the water the pump will work again. This operation is called the “start” or “prime” of the pump.