An apparatus for the application of topical negative pressure therapy to a site (18, 82) on the skin of the body of a mammal, the apparatus comprising: a dressing (14, 80) configured to sealingly surround the site, the dressing comprising: a base portion configured to be supported by the skin surrounding the site, the base portion comprising an aperture formed axially therethrough; a detachable portion removably supportable by the base portion; and a flexible membrane removably supportable by the base portion, the flexible membrane being configured to at least cover the aperture formed in the base portion; a conduit in fluid communication with the dressing; a first reduced pressure generation device being a piston and cylinder device and a second reduced pressure generation device being a piston and cylinder device, both in fluid communication with the conduit; and a valve member in fluid communication with the conduit and the first and second reduced pressure generation devices, the valve being a one way valve, both first and second reduced pressure generation devices being removably connectable to the valve member, each of the base portion, the detachable portion, and the membrane are formed from a substantially impermeable material; the dressing is configured to form a hermetically sealed enclosure over the site when the detachable portion and the flexible membrane are supported by the base portion; and characterized in that the first and second reduced pressure generation devices are arranged in parallel so that they can individually or simultaneously provide reduced pressure to the site. a dressing (14, 80) configured to sealingly surround the site, the dressing comprising: a base portion configured to be supported by the skin surrounding the site, the base portion comprising an aperture formed axially therethrough; a detachable portion removably supportable by the base portion; and a flexible membrane removably supportable by the base portion, the flexible membrane being configured to at least cover the aperture formed in the base portion; a conduit in fluid communication with the dressing; a first reduced pressure generation device being a piston and cylinder device and a second reduced pressure generation device being a piston and cylinder device, both in fluid communication with the conduit; and a valve member in fluid communication with the conduit and the first and second reduced pressure generation devices, the valve being a one way valve, both first and second reduced pressure generation devices being removably connectable to the valve member, each of the base portion, the detachable portion, and the membrane are formed from a substantially impermeable material; the dressing is configured to form a hermetically sealed enclosure over the site when the detachable portion and the flexible membrane are supported by the base portion; and characterized in that the first and second reduced pressure generation devices are arranged in parallel so that they can individually or simultaneously provide reduced pressure to the site. a base portion configured to be supported by the skin surrounding the site, the base portion comprising an aperture formed axially therethrough; a detachable portion removably supportable by the base portion; and a flexible membrane removably supportable by the base portion, the flexible membrane being configured to at least cover the aperture formed in the base portion; a conduit in fluid communication with the dressing; a first reduced pressure generation device being a piston and cylinder device and a second reduced pressure generation device being a piston and cylinder device, both in fluid communication with the conduit; and a valve member in fluid communication with the conduit and the first and second reduced pressure generation devices, the valve being a one way valve, both first and second reduced pressure generation devices being removably connectable to the valve member, each of the base portion, the detachable portion, and the membrane are formed from a substantially impermeable material; the dressing is configured to form a hermetically sealed enclosure over the site when the detachable portion and the flexible membrane are supported by the base portion; and characterized in that the first and second reduced pressure generation devices are arranged in parallel so that they can individually or simultaneously provide reduced pressure to the site. each of the base portion, the detachable portion, and the membrane are formed from a substantially impermeable material; the dressing is configured to form a hermetically sealed enclosure over the site when the detachable portion and the flexible membrane are supported by the base portion; and characterized in that the first and second reduced pressure generation devices are arranged in parallel so that they can individually or simultaneously provide reduced pressure to the site.