The present invention relates to a check valve, and to a device having a check valve, and to a method of cleaning a check valve. In order to provide a check valve or a device having a check valve or a method of cleaning a check valve, in which sufficient cleaning of the non-flow-facing regions of the valve closing body is also ensured, it is proposed according to the invention that an element reducing the flow cross-section is provided in a region of the opening stop in addition to the opening stop so that, when the valve closing body is in the open position and the fluid flows through the check valve counter to the blocking direction, a non-flow-facing region of the surface of the valve closing body has at least an average wall shear stress of 50% compared to an average wall shear stress of a flow-facing region of the surface of the valve closing body.

A combination flow control and reverse flow check valve controls the flow of fluid in a desired downstream direction and limits undesired backflow of liquid in an upstream direction into a fluid source such as a reservoir. The flow control and reverse flow check valve may include a housing having a fluid conveying channel with an upstream end configured for mounting to the liquid source and a downstream end for discharging fluids, a flow control valve positioned between the ends, and a check element positioned in the channel between the flow control valve and the downstream end. The check element is advantageously positioned between the flow control valve and the downstream end of the housing to prevent possible contaminants in a backflow liquid from reaching the flow control valve.

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.