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Hydraulic Pumps

Hydraulic pumps are devices that convert the hydraulic energy of liquids under pressure into mechanical energy. Some pumps that are used to transmit hydraulic fluids are also sometimes called hydraulic pumps. Because of the wide variety of contexts in which hydraulic systems are employed, hydraulic pumps are very important industrial, commercial and consumer utilities.

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Industry Information
View A Video on Hydraulic Pumps- A Quick Introduction

The construction, automotive manufacturing, excavation, agriculture, defense contracting and manufacturing industries are just a few examples of operations that utilize the power of hydraulics in every day processes. In many of the contexts in which hydraulic machinery is used, hydraulic pumps, also sometimes erroneously referred to as hydralic pumps or hydrolic pumps, are often employed for the transmission of hydraulic fluid from one place to another. In some instances, as with electric hydraulic pumps, the transfer of energy from hydraulic to mechanical is the end goal, with the pump mechanism serving as a generator. In other cases, however, the energy is expelled by means of high pressure streams that help to push, pull and lift heavy loads. Hydraulic gear pumps, hydraulic piston pumps and hydraulic clutch pumps, which operate in slightly different ways, are all utilized in heavy machinery for their versatility of motion and directionality. Hydraulic ram pumps and hydraulic water pumps are widely used to transfer water. The design of these pumps dictates that, although a small amount of external energy is needed to initiate the action, the weight of the water and its movement can create enough pressure to operate the pump continuously thereafter. The initial energy is produced in many ways. The simplest form is the hydraulic hand pump which requires a person to manually pressurize the hydraulic fluid. Portable 12V hydraulic pumps operate off of batteries and are useful in emergency situations, as are air hydraulic pumps, which need only an air compressor to run. Hydraulics pumps are used in a broad array of industries and machines. Despite the versatility and adaptability of these mechanisms, similar operating processes are behind them all.

Though specific operating systems are variable, all hydraulic pumps have the same basic components. A reservoir is needed to house the fluid not being processed and hoses or tubes are needed to transport the viscous liquids. The solution is transported to the hydraulic cylinder, which holds some of the most important mechanical components of the entire system. Within the cylinder, or cylinders as there are sometimes several, is a piston or gear system and two valves. On one end is the intake check valve with the discharge check valve being located on the opposite end. As with the cylinder, some systems have just one piston or gear cog while others have multiple. When the pump is working, the piston is withdrawn. This creates a vacuum that draws hydraulic fluid from the reservoir, through the hosing and intake valve and finally into the cylinder. When the piston is returned to its original position and the check valve closes, the fluid becomes pressurized. This pumping action is repeated at variable speeds until enough pressure has been built up in the cylinder to force the fluid to pass through the discharge valve. This creates the energy needed to work the attached machinery and move the intended load.

While this process is generally the same, there two main categories of hydraulic pumps to be considered: piston pumps and gear pumps. Within the piston grouping are axial and radial piston pumps. Axial pumps provide linear motion, while radial pumps can operate in a rotary manner. The gear category of pumps is also divided into two groupings, internal gear pumps and external gear pumps. No matter piston or gear, each type of hydraulic pump can be either a single-action or double-action pump. Single-action pumps can push, pull or lift in only one direction, while double-action pumps are multidirectional. The intended use of the pump should be considered when selecting a particular type, as some may carry out only one task, while others allow more flexibility. The material composition of the pump should also be considered in an application-specific context. The pistons, gears and cylinders are often made of durable materials such as aluminum, steel or stainless steel, which can endure the constant wear of repetitive pumping. The materials must hold up not only to the process itself, but to the hydraulic fluids as well. Oils, esters, butanol, polyalkylene glycols and corrosion inhibitors are often included in composite fluids, though simply water is also used in some instances. These fluids vary in terms of viscosity, operating temperature and flash point.

Along with material considerations, manufacturers should compare operating specifications of hydraulic pumps to ensure that intended use does not exceed pump capabilities. Continuous operating pressure, maximum operating pressure, operating speed, horsepower, power source, maximum fluid flow and pump weight are just a few of the many variables in hydraulic pump functionality. Standard measurements such as diameter, length and rod extension should also be compared. As hydraulic pumps are used in motors, cranes, lifts and other heavy machinery, it is integral that they meet operating standards. Insufficient pumps can lead to mechanical failure in the workplace, which can have serious and costly repercussions. Although pump failure has been unpredictable in the past, new diagnostic technologies continue to improve on detection methods that relied upon vibration signals alone. Measuring discharge pressures allows manufacturers to more accurately predict pump wear. Discharge sensors can be easily integrated into existing systems, adding to the safety and versatility of the hydraulic pump.

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Images Provided by Star Hydraulics, Inc.


Types of Hydraulic Pumps

  • 12V hydraulic pumps are hydraulic power units that run off of 12 volts of direct current provided by a battery or motor.
  • Air hydraulic pumps are energy-saving pumps that are operated by a compressed air source and require no energy to maintain system pressure. In both the single and two-stage air hydraulic pumps, air pressure is simply converted to hydraulic pressure, and they stall when enough pressure is developed.
  • Axial piston pumps have pistons that make the strokes in the same direction along the centerline of the cylinder block.
  • Centrifugal pumps are non-positive displacement pumps that are used in hydraulics requiring a large volume of flow. Centrifugal pumps operate at fairly low pressures and are either diffuser or volute types.
  • Electric hydraulic pumps use hydraulic cylinders to provide electric power to machinery.
  • Fixed-displacement pumps are pumps whose output can only be altered by changing the drive speed.
  • High pressure pumps are pumps that operate at extremely high pressures. High pressure pumps operate in the range of 3,000 to 70,000 psi.
  • Hydraulic pumps are extremely simple yet effective mechanisms for moving liquids. "Hydralic" is actually a misspelling of "hydraulic;" hydraulic pumps rely on the power provided by hydraulic cylinders to power various machines and mechanisms.
  • Hydraulic clutch pumps are assemblages in which a clutch assembly is accompanied by a pump that allows the user to apply the required pressure to either engage or disengage the clutch system.
  • Hydraulic gear pumps have intermeshing gears that displace fluid, creating mechanical power.
  • Hydraulic hand pumps are manually operated to pressurize a hydraulic system. Hydraulic hand pumps are often used to calibrate instruments.
  • Hydraulic piston pumps use a plunger-like apparatus to move hydraulic fluids through a cylinder in order to effectively raise the pressure for machinery, allowing it to push, pull and lift heavy loads.
  • Hydraulic pumps convert hydraulic energy to mechanical power.
  • Hydraulic ram pumps require virtually no maintenance, as they have only two moving parts. Water from an elevated water source enters one of two chambers through a relatively long, thick pipe, developing inertia as it moves down to the second chamber, which starts the pump.
  • Hydraulic water pumps use hydraulic power to move water from one place to another.
  • Hydraulics pumps are specially designed mechanisms used in industrial, commercial and residential settings to create useful energy from the pressurization of various viscous fluids.
  • Hydrolic pumps are mechanisms that are used to transmit pressurized fluid. "Hydrolic" is actually a misspelling of "hydraulic."
  • Nonpositive-displacement pumps discharge liquid in a constant flow.
  • Positive displacement pumps discharge liquid volumes at separate periods.
  • Radial piston pumps use pistons that are arranged in a design similar to wheel spokes and are situated in a small cylindrical block.
  • Reciprocating pumps depend on reciprocating motion in order to transmit fluid from the inlet side to the outlet side.
  • Rotary pumps are a type of positive-displacement pump that use rotational motion to transfer liquids from the pump inlet to the outlet.
  • Two-stage electric hydraulic pumps are pumps in which the clamps and cylinders are quickly extended by high flow at low pressure in the first stage of operation. In the second stage, piston pumps build pressure to a preset level and then maintain that level.
  • Two-stage pumps are composed of two separate pump assemblies that are contained in a single housing.
  • Variable-displacement pumps have cylinder sizes that are changeable.

Hydraulic Pumps Terms

Accumulator - A container that stores fluid under pressure and is utilized as a source of energy or to absorb hydraulic shock. Accumulator types include piston, bladder and diaphragm.

Cavitation - A circumstance that occurs in pumps when existing space is not filled by available fluid. Cavitation will deteriorate the hydraulic oil and cause erosion of the inlet metal.
 
Closed-Center System - A system in which the pump continually operates against a load, even in the neutral condition.
 
Cylinder - A hydraulic actuator constructed of a plunger or piston inside a cylindrical housing. The piston or plunger operates because of pressurized liquid.
 
Displacement - The amount of liquid transferred from the inlet of the pump to the outlet in a single revolution. Displacement can be fixed or variable.
 
Flow Rate - The amount of liquid volume that passes a given point in a given time. Flow rate is commonly measured in gallons per minute (gpm).
 
Head - Vertical distance measured between two stages in a liquid.
 
Hydraulic Actuator - The piece of machinery that receives pressure from the energized fluid and then converts it to motion and mechanical force.
 
Hydraulic Filter - A device that filters out impurities in the liquid used to create mechanical energy.
 
Hydraulic Hoses - A relatively thick hose that transfers liquids to and from hydraulic pumps.
 
Hydraulic Power Unit
- Any device used to convert potential energy into kinetic energy within a hydraulic system. Motors and manual energy are both sources of power in hydraulic power units.

Hydraulic Tester - A device used to troubleshoot and check hydraulic powered system components.
 
Hydraulic Valve - A device used to regulate water distribution in hydraulic applications.
 
Hydraulics - The science dealing with the transmission of force through the medium of a contained fluid.
 
Oil - A slippery and viscous liquid that is not miscible with water. Oil is often used in conjunction with hydraulic systems because it cannot be compressed.
 
Open-Center System - A system in which the yield of the pump has a free-flow passageway back to the reservoir, while in the neutral condition.
 
Piston - A device used for converting hydraulic power to mechanical energy. In hydraulic pumps, the piston is responsible for pushing down and pulling up the ram.
 
Pump - A mechanical device that transports liquids and gases by suction or pressure.
 
Ram - A hydraulic mechanism that uses the kinetic energy of a flowing liquid to force a small amount of the liquid to a reservoir contained at a higher level.
 
Resistance - In hydraulics, the condition engendered by an obstruction or restriction in the flow path.
 
Seal - A fastener designed to provide a perfect and tight closure. Seals prevent environmental materials from contaminating hydraulic assemblies.
 
Valve - A device used to regulate the amount of hydraulic or air flow. In the closed position, there is zero flow, but when the valve is fully open, flow is unrestricted.
 
Velocity Pressure
- Pressure in a hydraulic system caused by kinetic energy.




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