BS 6280:1982 pdf free.Method of vacuum (backsiphonage) test for water-using appliances.
This British Standard BS 6280 describes a method for applying a vacuum test to water-using appliances to determine that they have an acceptable degree of protection against backflow or backsiphonage.
NOTE The titles of the publications referred to in this standard are given on the inside back cover.
2 Definitions
For the purposes of this British Standard the following definitions apply.
2.1
critical level
the constant steady water level in a water appliance or water-using apparatus protected by a backflow prevention device when the rate of inflow of water through the feed pipework upstream of the device is the lesser of 2 m/s or that caused by a pressure of 6 bar1 upstream of the device and with all normal outlets (with the exception of overflows) from the appliance or apparatus closed.
2.2
choking flow
the condition when reduction of the downstream pressure reaches a critical value at which the mass flow rate no longer increases when a compressible fluid, such as air, flows through a throat or orifice at constant pressure upstream of the orifice
NOTE The critical value of the downstream pressure for air is about. 0.53 times the upstream pressure.
3 Apparatus
3.1 General. The test apparatus shall be arranged and constructed as shown in Figure 1 so that the absolute pressure measured near the appliance under test on its supply side remains less than 0.5 bar for at least 5 s.
NOTE These conditions indicate the existence of choking air flow.
Details of the components are given in 3.2 to 3.6.
3.2 Vacuum vessel and connecting pipework, of sufficient strength to support a total vacuum safely. The vacuum vessel shall be provided with a drain cock to remove any water drawn into the vessel during the test.BS 6280 pdf download.