In a trochoidal-type machine, the friction and wear due to the apex seal is a major problem. In order to increase the efficiency and reliability of this type of machine, we propose to replace the apex seals by tight running clearances. A peritrochoid with its special conjugate envelope is a good candidate for a trochoidal-type machine without apex seal. This paper presents its geometry attributes and pressure processes inside the pockets. First, the coordinates of contact point and pocket volumes at any shaft angle are derived. Then, the pressure processes inside the pockets are simulated with simplified valves. Finally, the effect of clearance on pocket pressure at different speeds is studied. The results indicate that a trochoidal-type machine without apex seal is worthy of further research and development.

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