A multi-stage, clam shell, vacuum pump comprises two housing components (12) which are to be sealingly connected to one another such that an array of chambers extending longitudinally from an inlet region of the pump to an outlet region of the pump is defined thereby. Sealing means (30) are provided within the vacuum pump, between the two housing components, to prevent transfer of fluid in to and out of the vacuum pump where said components are connected. An array of discrete, elongate channels (33, 34, 36, 38) is provided, located between the sealing means (30) and the array of chambers (14, 16, 18, 20, 22). The channels serve to protect the sealing means (30) from fluid that passes through the chambers during operation of the vacuum pump. Each channel is configured to receive a barrier fluid having a different pressure than a barrier fluid to be received by an adjacent channel.