How does "oil entrapment" occur in direct-coupled single-screw pumps? How can it be alleviated?

2026-01-15 14:41:06

Oil entrapment is a common problem in positive displacement hydraulic pumps, and direct-coupled single-screw pumps are no exception. The primary cause is the presence of a closed volume between the suction and discharge chambers, and the size of this volume fluctuates. Specifically, when the pump's closed working volume, after being fully filled with oil, transfers to the discharge chamber, a dead volume forms. If the size of this dead volume fluctuates, the hydraulic oil within it is squeezed or expanded, creating localized high pressure or cavitation, leading to oil entrapment.

In direct-coupled single-screw pumps, this oil entrapment can cause significant vibration and noise in the external gears, impacting system operation. Furthermore, since hydraulic oil is incompressible, oil entrapment can also subject the pump's internal components to excessive pressure shocks, accelerating wear and reducing pump life. To alleviate oil trapping in direct-coupled single-screw pumps, the following measures can be taken:

Introducing unloading grooves: Unloading grooves can be created on the front and rear covers or floating sleeves of the pump to minimize the dead volume. When the enclosed working volume decreases, the unloading groove connects it to the pressure chamber; when the enclosed working volume increases, the unloading groove connects it to the suction chamber. This prevents excessive compression or expansion of the hydraulic oil within the dead volume, thereby alleviating oil trapping.

Optimizing pump design: By improving the pump's structural design, such as adjusting gear contact and optimizing the angle of the oil distribution window, the dead volume can be reduced or avoided, thereby reducing the likelihood of oil trapping.

Improving machining accuracy: Ensure that all pump components meet machining accuracy requirements to reduce oil trapping caused by manufacturing errors.

Selecting appropriate materials: Using wear-resistant and corrosion-resistant materials for pump components can extend the pump's service life and reduce oil trapping caused by component wear.