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Boiler Fill & Makeup Water Valves

Boiler fill valves are used to provide a supply of fresh water for a hot water boiler system - whether newly installed or recently drained/flushed. Their main purpose is to reduce the incoming water pressure to a desired level and prevent back-flow of system water (since it can contain sludge, rust inhibitors and other chemicals) into the potable water supply.

About Boiler Feed Valves

"Fill" or "feed" valves, as the name suggests, are intended for supplying the boiler and the heating system with water. While fill/feed valve generally implies only the pressure regulating valve, the make-up water package nearly always include a backflow preventer, which stops the system water from going back into the drinking water supply. These two, often sold as a factory-assembled combo are very common for new boilers installs.

Most boiler fill valves are similar in design and specs (but could use different quality of materials - hence the price difference), and have a 10-25 psi adjustable outlet pressure, often factory set to 12 or 15 psi. They are simply pressure reducing valves designed for boiler feeding applications. Some models may utilize a built-in check valve.
Dual check backflow preventers with atmospheric vent are devices intended to prevent the reverse flow of boiler system water into the potable supply. How it works - under normal operating conditions, supply/inlet pressure keeps the vent closed, but in the event of zero supply pressure or backsiphon, the vent is opened, allowing contaminated water to drain through the vent.