The 51-Series is our Heavy-Duty water pump. It provides high volume water flow with reduced pump cycling, thanks to the large five-chamber diaphragm. These models are designed to run on water systems with no accumulator tank necessary, and up to five fixtures! It is also suited for use with a holding tank water system, as may be found in a boat, RV or remote cabin. It provides up to 5.5 gallons per minute. The 51-Series pumps are self-priming, and can run dry without damage. This automatic demand water system pump has a built-in pressure switch, which automatically starts and stops and stops the pump when the faucet is opened and closed. They are easy to install, service and winterize.