An apparatus for sealing a puncture through tissue, the apparatus comprising: a positioning assembly including an expandable member disposed at a distal portion of the positioning assembly; a tubular member carrying a sealant a support member advanceable through the tubular member and adjacent the sealant, wherein the positioning assembly is configured to move axially within the support member; and a handle comprising a deployment mechanism and a depressible button, wherein the button is provided in a first position in which the deployment mechanism is operatively coupled to the tubular member and operatively uncoupled from the support member, characterised in that, the button has a partially depressed position between the first and a second position, wherein in the partially depressed position the deployment mechanism is operatively coupled to the support member, the tubular member is positioned proximally compared to its position when the button is in the first position, the sealant disposed at the distal portion of the positioning assembly is at least partially exposed, and the support member is in substantially the same position as it is when the button is in the first position, the button being moveable relative to the handle from the first position to the second position for the deployment mechanism to retract the tubular member proximally and advance the support member distally, the apparatus further comprising a first rack operatively coupled to the tubular member and a second rack operatively coupled to the support member, and wherein at least one of the first and second racks has a discontinuous region to delay distal advancement of the support member until the button is in said partially depressed position. a positioning assembly including an expandable member disposed at a distal portion of the positioning assembly; a tubular member carrying a sealant a support member advanceable through the tubular member and adjacent the sealant, wherein the positioning assembly is configured to move axially within the support member; and a handle comprising a deployment mechanism and a depressible button, wherein the button is provided in a first position in which the deployment mechanism is operatively coupled to the tubular member and operatively uncoupled from the support member, the button has a partially depressed position between the first and a second position, wherein in the partially depressed position the deployment mechanism is operatively coupled to the support member, the tubular member is positioned proximally compared to its position when the button is in the first position, the sealant disposed at the distal portion of the positioning assembly is at least partially exposed, and the support member is in substantially the same position as it is when the button is in the first position, the button being moveable relative to the handle from the first position to the second position for the deployment mechanism to retract the tubular member proximally and advance the support member distally, the apparatus further comprising a first rack operatively coupled to the tubular member and a second rack operatively coupled to the support member, and wherein at least one of the first and second racks has a discontinuous region to delay distal advancement of the support member until the button is in said partially depressed position.