Differential pressure monitoring device

An assembly including a differential pressure switch for a hybrid air bag inflater, comprising:

• an elongated cylindrical tank for receiving an expandable type gas at a first pressure P1,
• a first sealed end on said tank having an igniter-gas generator mounted thereon for heating and expanding said expandable type gas for use in inflating an air bag,
• a second sealed end on said tank having said differential pressure switch mounted thereon inside of said tank for monitoring said first pressure P1 in said tank,
• said pressure switch having a switch body attached to said second sealed end,
• electrical lead means extending through said switch body and through a wall of said tank to a point outside of said tank,
• a mandrel on said switch body,
• a movable piston extending through a recess in said mandrel,
• contact switch means coupled to said piston for opening or closing an electrical path between said electrical lead means,
• a sealed capsule mounted juxtaposed said piston and said mandrel for actuating said contact switch means, and
• said capsule containing a gas at a threshold pressure P2 where P1 is greater than P2 when the gas pressure P1 in said tank is sufficient to fill an air bag.