Yes, RESPIRATOR is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, S 1, P 3, I 1, R 1, A 1, T 1, O 1, R 1.

Is it a valid word?

RESPIRATOR is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a breathing device for administering long-term artificial respiration
a protective mask with a filter; protects the face and lungs against poisonous gases

Also: gas helmet.

Not playable in Scrabble US: GASMASK.