This question is asked often…and my answer would be based on comparing an air-powered syringe system to a positive displacement syringe system. I’ll answer the question in the order of criteria that you listed.

1. Repeatability – Air-powered dispensing is based on a time-pressure system. The operator steps on a foot pedal or actuates a finger switch and a pulse of air is sent to the syringe reservoir for a pre-set time, usually in milliseconds. The air pushes the fluid through the dispensing tip and a precise amount of is applied to your part.

   In a positive displacement syringe system, the operator steps on a foot pedal which actuates a motor, usually a stepper motor. The motor is attached to a rod that pushes down on the fluid in the syringe reservoir, usually a predetermined distance or “steps” of the motor. Once the rod has moved it’s pre-set distance, the stepper motor reverses direction which retracts the rod backwards to relieve the pressure against the fluid to prevent dripping or excess flow.

   Here’s the thing…both systems have their place. If you are working with a two part epoxy with a limited working time – usually 30 minutes or longer – and you don’t want to be making constant adjustments over the working life of the epoxy, then the positive displacement system would probably be the best way to go…for now. New technology in air-powered dispensing is coming to allow for automatic changes for fluids that change viscosity. Until then you can continue to use the positive displacement syringe system for your two-part epoxy. For all other fluids, I think the air-powered dispensers are the way to go. First of all, they are easier to use and easier to set-up than a positive displacement syringe system. More importantly, both systems are comparable in repeatability. The theory of how positive displacement syringe systems work is good, however, there are some flaws that might not make it as accurate as most people would think.

2. Speed of Operation– Hands-down, air powered dispensers are faster and can provide higher cycle rates than a positive displacement syringe system…period!
3. Ease-of-Use – This is always a subjective topic…what might be difficult for one person is easy for another person. Based on feedback from hundreds of companies that have tried both, the air-powered dispensers always win the “ease-of-use” debate. Again, this doesn’t mean that the positive displacement dispensers don’t have their place, it just means that a majority of people think that air-powered dispensers are easier to use, easier to set-up, and easier to train their operators on.