Pilot Sprinkler : An automatic sprinkler or thermostatic fixed temperature release device used as a detector to pneumatically or hydraulically release the system actuation valve
NFPA 15 Standard for Water Spray Fixed Systems For Fire Protection, 2001 ed. https://law.resource.org/pub/us/cfr/ibr/004/nfpa.2 5.2002.pdf, (Std: Wtr Spray Fixed Sys for Fr Prac - Amer) {183 NFC}