BS EN 15611:2020,Railway applications – Braking – Relay valves.BS EN 15611:2020 pdf free download.
BS EN 15611:2020 is applicable to relay valves designated to control the brake cylinder pressure of compressed air brakes fitted to railway vehicles, in association with an air brake distributor valve or other control device. It covers one stage relay valves and relay valves adjusting the brake cylinder pressure in response to a change in vehicle speed or load that is either continuously variable or in two or more stages, i.e. empty – loaded.
BS EN 15611:2020 specifies the requirements for the design, manufacture and testing of relay valves.
2 Normative references
EN 14478: 2017, Railway applications-Braking-Generic vocabulary
EN 15355: 2019, Railway applications-Braking-Distributor valves and distributor-isolating devices;
EN 15625: 2008+A1: 2010, Railway applications-Braking-Automatic variable load sensing devices;
EN 45545-1: 2013, Railway applications- Fire protection on railway vehicles-Part 1: General;
5 Design and manufacture
5.1 General
A relay valve shall enable a distributor valve or a brake control unit to be used withoutany vehicle specific modification to the distributor or the brake control unit, related to the brake cylinder volume. This includes the independence of the brake application and release times, the inshot feature and the output pressure development for any output (brake cylinder and piping) volume.
The use of a relay valve shall not alter any of the characteristics of the distributor and /or a brake control unit that are not specified in this standard.
The use of a relay valve shall enable the brake cylinder pressure to be maintained between prescribed limits.These limits may be defined by different brake modes or speed-dependent requirement or where  there is a requirement to maintain a nominal constant brake performance irrespective of load.
Table 2 below provides a description of relay valve types described in this standard in comparison to EN15611:2010.