Flow characteristics of an improved version of piston-type flowmeter are presented. The piston is mounted on the bearings, and the piston is allowed to rotate by the fluting on its lateral surface. Numerical solutions are obtained to describe the flow details inside the flowmeter chamber for realistic operating conditions. The flowmeter linearity between the force acting on the piston and the flow rate is shown to be preserved. The numerically-constructed patterns of meridional flows are depicted. The profiles of the pressure on several key surfaces are revealed. Assertions are made of the practical utility of this design of flowmeter. (C) 1997 Published by Elsevier Science Ltd.