Yes, DIAPHRAGM is a Scrabble word!

Letter values in Scrabble US: D 2, I 1, A 1, P 3, H 4, R 1, A 1, G 2, M 3.

Is it a valid word?

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

a mechanical device in a camera that controls size of aperture of the lens
(anatomy) a muscular partition separating the abdominal and thoracic cavities; functions in respiration
a contraceptive device consisting of a flexible dome-shaped cup made of rubber or plastic; it is filled with spermicide and fitted over the uterine cervix
electro-acoustic transducer that vibrates to receive or produce sound waves

Also: contraceptive diaphragm.