A diaphragm pump such as the Pulsafeeder Pulsatron C series LC54SA-VHC1-XXX uses a positive displacement diaphragm powered by an electronic solenoid. There is no motor needing a fan for cooling so the pump is completely enclosed and rated for outdoor use. There is a stroke length knob to adjust flow down to as low as 20% of output and the more expensive pumps also come with a stroke frequency knob that slows the stroke down. With both these controls you can lower the pump down to about 1% output. This can be a very handy feature. The Pulsafeeder pump is warranted for 2 full years.
Peristaltic pumps like the Stenner model 85MHP17 have advantages too. The biggest is the ability never to lose prime. This is extremely important when feeding chlorine or other gasous chemicals. Any bubbles that may be present in the line are just pushed through the pump. It accomplishes this by using a special tube that is inserted between three rollers and the pump head. The rollers turn powered by a mechanical motor squeezing the tube pushing the chemical along with the bubbles into the injection point. The tube typically lasts about 1 year or so before you have to replace it. The Stenner pumps are warranted for 1 full year.
Both the Pulsafeeder pump and the Stenner pump along with the Milton Roy LMI pumps are very high quality. Each manufacturer stands behind their pumps 100% and are eager to assist anybody that may have a problem. Take it from me, I have been selling these pumps for over 22 years.
