Although the fleet of ten 2-6-0+4 engines that handled most of the line work were nominally similar, they were actually built in small batches over a long period by different builders. No.31 was the oldest, a 1913 Maffei product originally built for the Pamplona-San Sebastian Railway and acquired by the PV in 1943. For many years No.31 was the preferred engine for the daily passenger train but by the end of 1980, the correo had stopped running and the old Maffei was hauling coal trains.
On 31 December 1980, No.31 was photographed crossing the viaduct over the Rio Sil at Santa Marina.