I think that this is a view looking westwards towards Pwllheli with the station buildings on the up platform hidden by the train headed by Standard 82020 , a class which had come on to the Cambrian system in the mid ' fifties in order to replace former Great Western classes , especially the Dukedogs , so long associated with the system . The Standard Class Three design was , however , restricted by limited water capacity to short duties and was replaced by larger members of the Standard Class Four design . Second only to Barmouth in importance on the Cambrian , Portmadoc had a two road locomotive shed dating back to Great Western Railway times , officially designated as a sub shed to Machynlleth .