![]() The internal disc opens and allows the flow of steam through the valve. Non-return valves are flow sensitive, and rely on the steam flow to open and close. The first valve must be automatic and the second should be outside-screw-and-yoke (OS&Y). For high-pressure applications involving multiple steam boilers with manholes that are connected to a common steam main, the steam connection from each boiler must be fitted with two stop valves. Per ASME standards, one NRV is required for one-boiler, high pressure applications (above 15 psig). Although the NRV should not be relied upon for primary shut-off, it does restrict the flow of steam back from the header into the boiler, which could be disastrous. The non-return valve is really just another safety device. In other words, they prevent steam from flowing back to the main header of the boiler, or back to a boiler that has failed or is off-line.Īn NRV can also be used to isolate a boiler during blowdown and shutdown, and to assist in returning a boiler to operation after any planned or unplanned maintenance. The main function of a non-return valve (NRV), otherwise known as stop or check valve, is to allow steam flow in one direction, and automatically prevent backflow. These valves are vital to protect the boiler and other plant equipment and are required by the ASME. You may not know this, but all Nationwide Boiler rental boiler systems come standard with a non-return valve. ![]()
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