the BMA controls the pump and is place in between the valve blocks servos and the receiver
here is a link to the servonaut site and the BMA page there is a PDF to download to give you a bit more info, it is near the top of the page
http://www.servonaut.de/shop/product...naut-bma.html&
link to PDF
http://www.servonaut.de/shop/media/p...o48rns5r4qb4b5