Tender Water Valve

[Runner]

Hi all,

I am building a LMS Black 5 basically of LBSC design. However I am unsure of the purpose of the tender water valve mounted on the front drag beam of the tender. Is it to control the water flow to the injector or to open/shut the return flow from the axle water pump? LBSC narratives and diagrams tend to indicate that that it does both, but obviously can't do both. My guess is that it opens/shuts the return flow from the axle water pump.

Thanks in advance

Brian