The Dometic PMA1000 115 V pump can support total air handler capacities from 16,000 to 23,000 BTU/h and ensures a top cooling performance. The fill assembly includes a hose connection, ball valve and pressure-reducing valve. The cushion of air in the expansion tank allows the water to expand and contract with temperature fluctuations. This relieves pressure that might otherwise result in leaks. The latest design includes a bladder-style expansion tank that prevents the air in the expansion tank from gradually dissolving into the water and being bled off. This maintains the protective cushion of air. The pressure gauge is connected to an inlet pipe on the pump for the most accurate reading of system return water pressure. Ensure your onboard comfort.