In an apparatus for pressure testing open-ended pipes or the like there is provided a novel sealing means to form an air-tight seal between the open end of a pipe to be tested and an end plate of a pipe supporting test fixture. The sealing means comprises a continuous, annular, yieldable sealing member of triangular cross-section supported on the end plate. A pneumatically expandable annular actuator is associated with the continuous sealing member. The sealing member is normally spaced radially and axially from the junction area of the pipe end and test fixture end plate. The pneumatically inflatable actuator is operative to expand the continuous yieldable sealing element radially and simultaneously to advance it longitudinally, whereby the triangular sealing member is tightly wedged into said junction area to form a preliminary seal. When test pressure is applied, it acts upon the triangular sealing member to increase the seal effectiveness.