Fluid suck-back refers to any fluid or blood upon the nozzle being sucked into the orifice of the jet gun injector and contaminating the drug reservoir which holds the next dosage to be fired. Fluid suck-back occurs after the injection has been administered.
This undesirable phenomenon is likely due to a combination of the unit being pressurized and a faulty ball check-valve which created a vacuum at the end of the injection.
The following illustrations demonstrate this phenomenon.
And where is the evidence?