This is a 3D model of a Backflow Preventer.

3D Model Annotations

Backflow Preventer

Backflow preventers are a type of check valve (non-return valve) used to prevent flow in a reverse direction to that which was intended. This particular 3D model shows a backflow preventer with two check valves and one relief valve.

Check Valve

This type of check valve consists primarily of a spring and disc. The disc presses against the seat in order to stop fluid flow. The spring provides residual force to close the valve. If the system pressure should exceed a given setpoint, the residual force of the spring will be exceeded, and the valve will open. Springs must be periodically inspected to ensure the desired lifting/opening pressure is maintained; corroded, dirty, or worn springs, may lead to the valve not operating as intended.

Relief Valve

Should the pressure between the two check valves exceed a certain value, the relief valve will open, and the pressure will be relieved. Relief valves are spring loaded pressure relief devices. Should the spring become worn over time, it may lift at a lower pressure. If the spring becomes dirty or corroded, it may lift at a higher pressure. For this reason, all relief valves should be periodically inspected and maintained (e.g. annually).

Main Inlet

Fluid flows into the valve through this connection.

Main Outlet

Fluid exits the valve through this connection.


The body is the main pressure boundary of the valve, it may be manufactured from a single piece or multiple pieces.

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