A diaphragm pump keeps the water system pressurized at all times. It’s like having running water, just like in a house.
The water pump creates and maintains water pressure. Theses pumps are pressure activated, so no On/Off switch is needed. When water pressure drops the pump automatically starts, until pressure is restored.
Many pumps need an accumulator as a buffer. The accumulator is like a pressure regulators so the pump does not need to start and stop often.
The SEAFLO 42-Series pump does not need an accumulator; it is a variable flow pump providing 55PSI and 3 gallons per minute. It is also self-priming and is capable of running dry without harming the pump.
So far these pumps have been excellent. We have two in our van build. They have a 4 year warranty, which I have not needed to test since they have been working without error. But I do have an extra one just in case there is a problem. They have variable flow to reduce cycling.