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The Tirvit has a simple cartridge, which

slips into the top of the housing without

the need to take apart the assembly. To

operate, the top of the cartridge is

depressed to engage with the top of the

needle. The canister opens briefly and

gas is injected into the bottle. A refill

canister was available to recharge the

cartridge. One refill was good for six

charges. In case the needle was

damaged, a few turns of a knurled nut

made it easily removed and replaced.