Plunger Pumps: Differences Between Open-Loop and Closed-Loop Pumps

Closed-type plunger pump : What is the difference between open-type pumps and closed-type pumps? Let’s examine each type separately below.

The circulation of an open pump system is : Fuel tank - pump - Control valve - User end - Fuel tank.

The circulation in a closed-loop pump system is: pump —User end—Pump.

As the name suggests righteousness In open-loop pumps, the circulation loop is open; in closed-loop pumps, the circulation loop is closed. The primary difference in performance lies in the fact that open-loop pumps can only transmit power in a unidirectional manner, and braking can only be achieved through throttling via various control valves; in contrast, closed-loop pumps support bidirectional power transmission and can implement regenerative braking.

When the circuit is open, the pump typically delivers flow in a single direction, which is reversed by a directional control valve. ; In closed-loop operation, the pump typically delivers flow in both directions by adjusting the swashplate or stator eccentricity to reverse the flow direction.

The concepts of open-loop and closed-loop pumps are generally applied to swash-plate axial piston pumps, particularly closed-loop designs. As far as I know, the swash plate is currently the only component that can be readily adjusted: by shifting the swash plate angle from a relatively large positive value to a relatively large negative value, the inertial mass of the swash plate is reduced, making it easier to adjust and enabling a faster response.

For both open-center and closed-center pumps, the basic approach to variable control is the same: it is achieved by adjusting the swash plate angle. As for other variable-control requirements, these can be tailored to the specific operating conditions of each application. The pressure-compensation and load-sensing features you mentioned—key variables in this field—are widely employed in both open-center and closed-center pumps and, in essence, constitute a valve-controlled feedback control system.

An open-loop hydraulic system is one in which the hydraulic pump draws oil from the reservoir, the oil flows through various control valves to drive the hydraulic actuators, and then returns to the reservoir via a directional control valve.

In a closed-plunger pump system, the hydraulic pump’s delivery line is directly connected to the actuator’s return line, creating a closed loop for the working fluid within the system piping. This compact configuration minimizes contact with air, making it more difficult for air to ingress into the system and thereby ensuring more stable fluid transmission.

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