The Effects of Direction of Rotation in Double-Helical Gear Pumps on Delivery Characteristics

Abstract

In double-helical gear pumps, it is clarified theoretically that delivery characteristics differ in accordance with the direction of gear rotation (called "forward rotation" when central part of the tooth curve first enters the gearing region, and "backward rotation" when ends of the tooth first enter the gearing region), and experiments are conducted using spur gear, single-helical gear and double-helical gear pumps. Results obtained are as follows : (1) Owing to fluid flow across the tooth curves being unfavourable, the theoretical characteristics at backward rotation are worse than at forward rotatio. (2) When there were pressure release ports on both sides of delivery and suction, or on delivery side only, the pumps operating under forward rotation always showed better total efficiencies than pumps operating under backward rotation and having the same type of release ports. (3) When the release port was on suction side only or when there was no release port, no distinct effect of direction of rotation on the total and volumetric efficiencies was observed. (4) Double-helical gear pumps operating under forward rotation showed total efficiencies higher than those of spur gear or single-helical gear pumps. (5) Double-helical gear pumps under backward rotation would have an efficiency equal to or worse than the efficiencies of spur gear or single-helical gear pumps.