Tandem Blow-Down Valve
ASME Code for pressure piping, B31.1, mandates two shutoff valves in series, for blow down piping systems from boiler water spaces. At least one of these must be slow opening. Two valves may also be combined into one body as long as they operate individually. This ensures that the failure of one doesn’t affect the other. One valve also provides isolation from the process while the other is used to blow off high-pressure condensate. No medium flows through the isolation valve while the Blow-Down Valve is still closed. The Blow-Down Valve experiences a strong abrasive flow upon opening.
The Tandem Valve eliminates issues that could occur having two separate valves by combining two valves in one body. Space is saved by eliminating the flanged connections, gaskets and bolting, (or welded piping connections) between separate valves