Because of the effect of well fluid pressure,temperature and axial force imposed on the plunger and pump barrel as sucker-rod pump being in operation,the annular clearance between the plunger and pump barrel appeared to be a reverted cone along the length of the plunger.Based on the principle of fluid dynamics in the wedge clearance,accurate and simple approximate formulas were derived for calculating the annular leakages as the axes of pump barrel and the plunger being parallel and not parallel.The formula...