BS EN 13434:2021 pdf free download – Devices to prevent pollution by backflow of potable water一Mechanical disconnector, flow actuated一Family G, Type B.
8 Design
81 General
a) The internal components of the device shall be accessible for inspection, repair or replacement. By design, the components shall be able to be refitted at their initial place, without ambiguity (impossibility of reversal, interchange of obturators, diaphragms, and springs). A visible mark is not sufficient.
b) Additional control devices shall not influence the safety function.
c) The settings of the springs shall be fixed and not adjustable.
d) The device shall comprise one pressure tapping and a visible indication on the device when the obturator is in the drain position. The pressure tapping is located on the inlet of the device.
e) Only the flow of water can operate the control of the internal components of the device.
8.2 Relief valve/Obturator
8.2.1 General requirements
In all the installation positions indicated by the manufacturer, any water retention shall not be possible within the intermediate zone.
The cross-section of the passage orifices and of the pilot tube for operation of the relief device shall be equal to or greater than an area of 12,5 mm2, In case of un-machined cross — sections the smallest dimension should be  4 mm. The outside pilot tube shall be made so as not to be vulnerable to any permanent deformation or rupture caused by external loading.
An air break to drain shall exist between any waste drain and any means of collecting the discharged water (floor, tundish, curb, sink).
The device with an air break to drain fitted shall evacuate the full relief flow rate as defined in 9.7.4. The air break to drain shall meet the dimensional requirements as specified in EN 1717. This air break to drain shall be:
— either directly incorporated into the device;
— or factory fitted;
— or supplied with the device.
In the latter case, the relief orifice of the device shall permit neither the fitting of a standardized threaded pipe, nor the connection ofa standardized pipe or shape, neither by adhesive, welding nor interlocking.
If applicable on the dimension “G’ of the outlet of the air break to drain (see in EN 1717:2000, Clause 9), it shall be possible to fit a standardized drain pipe (Standard EN 13 29-1 pvc compact or EN 1453-1 vc with structured walls).
The opening of the drain shall be equal or larger than the outlet of the device.
8.2.2 Mechanical Disconnector Family G, Type B
8.3 Disconnection distance
In drain position the obturator shall close the opening from upstream zone to the intermediate zone. The disconnection distance shall be at least 20 mm.
The drain port shall be closed, before flow condition is achieved. The passage orifice of the drain port shall be at least equal to the minimum cross-section of the outlet water way (downstream).
9 Characteristics and tests
9.1 General
Performance tests shall be carried out on the device as installed in accordance with the manufacturer’s technical documents.
If not specified all tests shall be performed with water at ambient temperature.