Some examples include a print substance reservoir for a printing system including a housing to be arranged within a printing device, the housing having an interior for containing a print substance and an exterior, an active vent valve to allow gases to travel from the interior to the exterior when the inlet is receiving the print substance, the active vent valve electrically energizable and de-energizable in response to signals corresponding to the transfer of the print substance into the housing, a passive inlet valve to open to allow air to enter the interior during removal of the print substance from the reservoir, the passive inlet valve biased to a closed position, and a passive pressure relief valve to open when pressure within the interior is greater than a predetermined pressure limit, the passive pressure relief valve biased to a closed position.