A fluid supply system for a printer, comprising: a first fluid supply cartridge and a second fluid supply cartridge; a source of pressurized air; a selection valve comprising: a sleeve comprising a first port to connect with the source of pressurized air, a second port to connect with the first fluid supply cartridge, a third port to connect with the second fluid supply cartridge, and a fourth port to connect with the atmosphere, and a core disposed rotatably inside the sleeve wherein the core is rotatable to a first position to fluidically connect the second port to the first port to pressurize the first fluid supply cartridge with the pressurized air, and fluidically connect the third port to the fourth port to vent the second fluid supply cartridge to the atmosphere, and wherein the core is rotatable to a different second position to fluidically connect the third port to the first port to pressurize the second fluid supply cartridge with the pressurized air, and fluidically connect the second port to the fourth port to vent the first fluid supply cartridge to the atmosphere; a flag to engage the core; a power source; and a cluster gear to engage the flag with the power source, wherein the power source provides friction torque for rotation of the flag which in turn is to rotate the core inside the sleeve, wherein the selection valve is to selectively couple the source of pressurized air to one of the first fluid supply cartridge and the second fluid supply cartridge in the fluid supply system to provide fluid to a printhead, one of the first fluid supply cartridge and the second fluid supply cartridge being coupled to the source of pressurized air at a time, and the other fluid supply cartridge being vented to the atmosphere. a first fluid supply cartridge and a second fluid supply cartridge; a source of pressurized air; a selection valve comprising: a sleeve comprising a first port to connect with the source of pressurized air, a second port to connect with the first fluid supply cartridge, a third port to connect with the second fluid supply cartridge, and a fourth port to connect with the atmosphere, and a core disposed rotatably inside the sleeve wherein the core is rotatable to a first position to fluidically connect the second port to the first port to pressurize the first fluid supply cartridge with the pressurized air, and fluidically connect the third port to the fourth port to vent the second fluid supply cartridge to the atmosphere, and wherein the core is rotatable to a different second position to fluidically connect the third port to the first port to pressurize the second fluid supply cartridge with the pressurized air, and fluidically connect the second port to the fourth port to vent the first fluid supply cartridge to the atmosphere; a sleeve comprising a first port to connect with the source of pressurized air, a second port to connect with the first fluid supply cartridge, a third port to connect with the second fluid supply cartridge, and a fourth port to connect with the atmosphere, and a core disposed rotatably inside the sleeve wherein the core is rotatable to a first position to fluidically connect the second port to the first port to pressurize the first fluid supply cartridge with the pressurized air, and fluidically connect the third port to the fourth port to vent the second fluid supply cartridge to the atmosphere, and wherein the core is rotatable to a different second position to fluidically connect the third port to the first port to pressurize the second fluid supply cartridge with the pressurized air, and fluidically connect the second port to the fourth port to vent the first fluid supply cartridge to the atmosphere; a flag to engage the core; a power source; and a cluster gear to engage the flag with the power source, wherein the power source provides friction torque for rotation of the flag which in turn is to rotate the core inside the sleeve, wherein the selection valve is to selectively couple the source of pressurized air to one of the first fluid supply cartridge and the second fluid supply cartridge in the fluid supply system to provide fluid to a printhead, one of the first fluid supply cartridge and the second fluid supply cartridge being coupled to the source of pressurized air at a time, and the other fluid supply cartridge being vented to the atmosphere.