In many liquid piping systems, it is vital that line pressure is maintained within relatively narrow limits. This is the function of the 101-16 Pressure Relief / Back Pressure Series of the SKYWIN valves. Installed in the main flow line, the standard Model 101-16 acts as a backpressure or pressure sustaining valve. In this configuration, the valve maintains a constant upstream pressure regardless of fluctuating downstream demand. When used in a bypass line, the same model will function as a relief valve, protecting the system against potentially damaging surges