Piston Pumps
Piston pumps are rotary units that utilize the principles of reciprocating pumps to generate fluid flow. Unlike traditional pumps with a single piston, these models feature multiple piston-cylinder combinations. A portion of the pump’s mechanism rotates around a drive shaft, creating the necessary reciprocating motions that draw fluid into each cylinder before expelling it to produce flow. There are two main types of piston pumps: axial and radial, both of which can be designed for fixed or variable displacement. The variable displacement types often allow for reversible (overcenter) displacement.
Both axial and radial piston pumps can be configured for variable and fixed displacement. Variable displacement pumps are typically larger and heavier due to the additional internal controls, which may include handwheels, electric motors, hydraulic cylinders, servos, or mechanical stems.
Axial-Piston Pumps
In an axial piston pump, the pistons move parallel to the drive shaft’s centerline, converting rotary motion into axial reciprocating motion. Most axial piston pumps are multi-piston designs that use check valves or port plates to control the flow of liquid from inlet to discharge.
The simplest form of an axial piston pump is the swashplate design. In this configuration, a cylinder block is rotated by the drive shaft, with pistons fitted into the bores of the cylinder block. These pistons are linked through piston shoes and a retracting ring, enabling the shoes to press against an angled swashplate. The arrangement of the Automotive Lift Repair Orlando ports in the valve plate allows the pistons to pass the inlet while being pulled outward and discharge when pushed back in. The pump’s displacement is determined by the size and number of pistons, as well as their stroke length, which changes with the swashplate angle.
In variable displacement models, the swashplate is mounted in a movable yoke. Adjusting the yoke changes the angle of the swashplate, thus increasing or decreasing the stroke of the pistons. The yoke can be adjusted using various controls, including manual, servo, or compensator methods.
Bent-Axis Pumps
Bent-axis pumps feature a drive shaft that rotates the pistons and a cylinder block, with a stationary valving surface positioned to face the cylinder block bores. The drive shaft is oriented at an angle to the cylinder block axis. As the drive shaft rotates, it causes the pistons and cylinder block to rotate as well.
Due to the angled orientation of the pistons relative to the valving surface, the distance between any piston and the valving surface changes throughout the rotation.
The Automotive Lift Repair Orlando valving surface is designed so that its inlet passage connects to the cylinder bores when the pistons are moving away and its outlet passage connects when the pistons move toward the surface. Thus, during pump rotation, the pistons draw fluid into their respective bores through the inlet chamber and expel it through the outlet chamber. Bent-axis pumps are available in fixed and variable displacement configurations, but they cannot be reversed.
Radial-Piston Pumps
In radial piston pumps, the Automotive Lift Repair Orlando pistons are arranged radially around a cylinder block, moving perpendicularly to the shaft’s centerline. These pumps can be classified into two primary types: those with cylindrical-shaped pistons and those with ball pistons. They can also be categorized based on porting arrangements, such as check valve or pintle valve, and are available in fixed, variable displacement, and variable reversible (over-center) displacement configurations.
In pintle-ported radial piston pumps, the Automotive Lift Repair Orlando cylinder block rotates around a stationary pintle within a circular reacting ring or rotor. The pistons are forced to follow the inner surface of the ring, which is offset from the cylinder block’s centerline. As the pistons move in and out of their bores, the porting allows them to take in fluid when moving outward and discharge it when moving inward.
The displacement of the Automotive Lift Repair Orlando pump is determined by the size and number of pistons and the length of their strokes, which can be adjusted by moving the reaction ring to change the eccentricity. Various controls are available to facilitate this adjustment.
Plunger pumps function similarly to rotary piston types, with fluid movement resulting from pistons reciprocating within fixed cylinders. Unlike rotary piston pumps, these cylinders do not rotate around the drive shaft. Pistons may be reciprocated via a crankshaft, eccentrics, or a wobble plate, with springs often returning them to their starting position. Because of their design, plunger pumps utilize inlet and outlet check valves instead of relying on port coverage for valving.
The construction of Automotive Lift Repair Orlando plunger pumps offers two significant advantages: they provide a tighter seal between the inlet and outlet, enabling higher pressures without excessive leakage, and they can pump fluids with poor lubricating properties, as lubrication for moving parts can be independent of the liquid being pumped. Their volumetric and overall efficiencies are comparable to those of axial and radial piston pumps.
Measuring Automotive Lift Repair Orlando Hydraulic Pump Performance
The volume of fluid a pump delivers per revolution is calculated based on the geometry of the oil-carrying chambers. However, a pump rarely delivers the theoretical amount of fluid, and the extent to which it approaches this value is termed volumetric efficiency. This efficiency is determined by comparing the theoretical delivery with the actual delivery, which can vary based on speed, pressure, and the pump’s design.
Mechanical efficiency is also typically less than ideal due to energy losses from friction, and the overall efficiency of a hydraulic pump is the product of its volumetric and mechanical efficiencies.
Pumps are commonly rated by their maximum operating pressure and their output in gallons per minute (gpm) or liters per minute (lpm) at a specified drive speed (rpm).
Matching Pump Power with the Load
Pressure compensation and load sensing are terms that describe features that enhance pump operation efficiency. While sometimes used interchangeably, these terms represent different operational enhancements.
To illustrate, consider a basic circuit with a fixed-displacement pump operating at a constant speed. This setup is only efficient when the load requires maximum power since the pump produces full pressure and flow regardless of the load. A relief valve prevents excessive pressure buildup by directing high-pressure fluid back to the tank when the system reaches the relief threshold.