Yes, REVOLVER is a Scrabble word!

Letter values in Scrabble US: R 1, E 1, V 4, O 1, L 1, V 4, E 1, R 1.

Is it a valid word?

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

a pistol with a revolving cylinder (usually having six chambers for bullets)
a door consisting of four orthogonal partitions that rotate about a central pivot; a door designed to equalize the air pressure in tall buildings

Also: six-gun, six-shooter, revolving door.