An insertable backflow preventer is presented. The backflow preventer is provided with a cylindrical housing. The housing has a flow transition zone, a proximal orifice/ball seat, a ball with a specific weight that equals or is close to the specific weight of the surrounding fluid, and a distal retaining screen. The housing can have a flange provided on the outside of the housing at one end to facilitate securing the valve in a pipe. The valve is self-cleaning, can be placed in any orientation in a pipe and has low hydraulic head-loss. The valve's unique cost-effective design provides for easy and relative quick installation, eliminates the need to reconfigure existing plumbing, and can be performance tested remotely. Properly installed, it can dramatically improve the security of, for example, potable water sources in a building or other context, and inasmuch as when installed it is not visible, it is tamper proof. The valve can be scaled to any size pipe or tube, and due to its internal flow dynamics is self cleaning. Multiple valves can be installed in series, and balls of varying specific weight can be used in each valve in such a series to allow for contexts where a range of fluids are sent through the same line, or to provide fail-safe operation in the event that contaminants change the specific gravity of the fluid.

A system for protecting a fluid supply from a contaminant includes an anchor check valve having an inlet end and an exit end, the anchor check valve adapted to allow fluid flow through the anchor check valve from the inlet end to the exit end but prevent fluid flow through the check valve from the exit end to the inlet end; a dry-barrel fire hydrant in proximate fluid communication with the anchor check valve, the dry-barrel fire hydrant having a valve operating mechanism; and a hydrant shoe coupled to the anchor check valve, the hydrant shoe having a valve assembly adjustably connected to the valve operating mechanism of the dry-barrel fire hydrant.