Melania:

Does your text actually say "branch monitors"? I believe that you need to provide additional context.

Be that as it may, have a look here:
http://www.sabo-esp.com/pdfs/sabo_general.pdf

You are correct about "monitores de espuma".
Para determinar el número requerido, se debe considerar la espuma
pérdida a causa del viento y de otros factores, especialmente cuando
los ***monitores de espuma*** se utilizan como protección primaria.

In determining actual solution flow requirements, consideration
shall be given to potential foam losses from wind and other factors,
especially where **foam monitors** are used as the primary protection.

This document speaks about "foam branch pipes", but I don't know if this is what you require (document in both English and Spanish): See pg. 83, for example. The word used for "branch" is "lanza".

El sistema más comun de distribución de la espuma de baja expansión incluye
la lanza de espuma y el monitor.

The most common systems to disburse the low expansion foam include the
foam branch pipe and the foam nozzle.