Pumps
Peristaltic Pumps
Peristaltic pumps are positive displacement pumps meaning they should theoretically provide a constant flow rate despite the pressure on the discharge end. These pumps work by a wheel of rollers squeezing flow through a tube so that the mechanical components of the pump never come in contact with the flow. The action is similar to squeezing toothpaste out of its tube. The flow rate provided by the pump varies with the speed of the rollers. If the rotational speed of the rollers is increased, the flow rate will increase. In the lab, we have Masterflex L/S Peristaltic Pumps. Most pumps are 100 rpm but there are a few 600 rpm. Check the back of the pump to see which type it is. Through Process Controller we are able to vary the speed on the digital pumps (pictured below). If a pump only has an ON/OFF switch, Process Controller will only be able to turn the pump on an off thus only providing one flow rate.
The tutorial for hooking up a peristaltic pump to Process Controller can be found here. 
Centrifugal Pumps
Centrifugal pumps are negative displacement pumps meaning that their flow rate depends on the pressure on the discharge end. Flow enters the white/gray piece (in the picture below) and is pushed upward through the black port (perpendicular to the entrance port) by a motor driven propeller. Each of these pumps are designed to operate efficiently at a given discharge pressure which can be found in the manufacturer's manual. The flow rate of these pumps cannot be set by Process Controller - it can only turn the pump ON or OFF. They can only be used with a stamp box as the voltage required to operate them is higher than can be supplied by the stamp box. 