A hydraulic piston pump works by using the back-and-forth movement of a piston within a cylinder to create pressure and move fluid.
The Core Principle
The fundamental operation relies on a simple mechanism. The basic working principle of a piston pump involves the reciprocating motion of a piston within a cylinder which alternately draws-in and discharges fluid, creating near continuous flow. This means the piston moves back and forth, first pulling fluid into the cylinder and then pushing it back out under pressure.
Key Components
A typical piston pump includes several essential parts:
- Piston: A cylindrical rod that moves inside the cylinder.
- Cylinder: A chamber in which the piston reciprocates.
- Inlet Valve: Allows fluid to enter the cylinder during the suction stroke but prevents it from exiting during the discharge stroke.
- Outlet Valve: Allows fluid to exit the cylinder during the discharge stroke but prevents it from re-entering during the suction stroke.
- Drive Mechanism: Provides the power to move the piston (e.g., a motor connected via a crankshaft or swashplate).
The Two Strokes Explained
The operation of a piston pump can be broken down into two distinct phases or strokes:
Suction Stroke (Intake)
- Piston Movement: The piston retracts (moves backward) inside the cylinder.
- Pressure Drop: This retraction increases the volume inside the cylinder, causing a pressure drop (creating a partial vacuum).
- Valve Action: The lower pressure inside the cylinder causes the inlet valve to open (if it's a check valve, the pressure difference pushes it open). The outlet valve remains closed, preventing fluid from returning.
- Fluid Intake: Atmospheric pressure (or pressure in the reservoir) pushes the hydraulic fluid through the inlet valve and into the cylinder, filling the space left by the retracting piston.
Discharge Stroke (Outlet)
- Piston Movement: The piston extends (moves forward) inside the cylinder.
- Pressure Increase: This forward movement decreases the volume, compressing the fluid and significantly increasing its pressure.
- Valve Action: The increased pressure inside the cylinder forces the inlet valve shut, trapping the fluid. The high pressure then forces open the outlet valve.
- Fluid Output: The now-pressurized fluid is pushed out of the cylinder through the outlet valve and into the hydraulic system where it can do work.
Achieving Near Continuous Flow
While a single piston creates pulses of flow, most hydraulic piston pumps used in systems requiring high pressure and consistent flow utilize multiple pistons operating in sequence (like in axial or radial piston pump designs). As one piston finishes its discharge stroke, another is beginning its, resulting in the near continuous flow mentioned in the basic working principle. This overlapping action smooths out the output pressure and flow rate.
Applications
Piston pumps are widely used in applications requiring high pressure and high efficiency, such as:
- Heavy construction machinery (excavators, cranes)
- Industrial press machines
- Agricultural equipment
- Aircraft hydraulic systems
By repeating the suction and discharge strokes, the piston pump continuously moves hydraulic fluid, providing the power needed for various hydraulic applications.
