A positive displacement pump is a Gear pump. It transfers fluid by continually enclosing a defined volume with interlocking cogs or gears and mechanically transferring it via a cyclic pumping motion. It produces a smooth, pulse-free flow that is proportionate to the rotational speed of its gears. A gear pump transfers fluid by enclosing a set volume inside interlocking cogs or gears and physically transferring it to give a smooth, pulse-free flow proportionate to the rotating speed of its gears.
External and internal are the two primary categories. Two identical, interlocking gears are supported by separate shafts in an external Gear pump. An internal gear pump features two different-sized interlocking gears, one of which rotates within the other. High-viscosity fluids, such as oil, paints, resins, and foodstuffs, are routinely pumped with gear pumps. They’re also the best choice for situations that need precise dosing or high-pressure output.
A Gear pump pumps fluid by displacement using the meshing of gears. They are one of the most frequent forms of hydraulic fluid power pumps. Pumping viscous liquids, such as certain viscous liquid hydrocarbons, and liquid fuels, lubricating oil pumping in machinery packages, hydraulic units, and fluid power transfer units, is a common use for gear pumps. The most common form of positive displacement pump is the gear pump.
Smaller Gear pumps normally spin between 1,700 and 4,500 revolutions per minute, whereas bigger units spin at less than 1,000 revolutions per minute. The fluid is carried between the teeth of two meshing gears in a gear pump, which provides flow. The pump housing and side plates, also known as wear or pressure plates, contain the chambers produced between neighboring gear teeth.
At the pump suction, a partial vacuum is generated; fluid flows in to fill the space and is conveyed around the gears’ discharge. The fluid is driven out as the teeth mesh at the discharge end. Gear pumps have a volumetric efficiency of up to 91 percent. Gear pumps feature tight tolerances and shaft support on both sides of the gears, which is common.
This enables them to operate at pressures of more than 200 bar gauges, making them ideal for high-pressure applications. Gear pumps aren’t typically well suited to abrasive or extremely high-temperature applications since they have bearings in the liquid and strict tolerances. Two or more gears mesh to create the pumping motion in gear pumps, which are rotary pumps. Typically, one of the gears can drive the other. The gerotor pump is the most basic variant of this sort of rotary pump.
Gear pumps are frequently employed in applications with small volume capacities and restricted space. These gear pumps can be mounted on a rotating shaft, such as a crankshaft, to lubricate crucial moving machine parts with oil. The fluid is carried between the teeth of two meshed gears of a gear pump, which creates flow.
The driving shaft spins one gear while the other is driven by it. The pump’s housing and side plates surround the pumping chambers produced between the gear teeth. The screw output to the die is controlled by gear pumps. The melt pressure and output volume to the die are controlled by a series of spinning gears within very tight tolerances, with little or no pulsing of the melt flow. This protects the die from upstream fluctuations such screw surging caused by material or machine differences.
OPERATION OF GEAR PUMPS
On the suction side of a gear pump, when the gears come out of the mesh, they produce increasing volume. As the gear teeth revolve, liquid flows into the cavity between the teeth and is trapped. In the pockets between the teeth and the casing, liquid might potentially move throughout the interior of the casing. This little flow is not able to travel through the gears. Under pressure, the meshing of gears drives liquid through the discharge port.
Running clearances between gear faces, gear tooth crests, and the housing cause a nearly constant loss in any pushed volume at a constant pressure in gear pumps. This means that volumetric efficiency may be poor at low speeds and low flows, hence gear pumps should be run near to their maximum capacity. Although pressure increases the loss through the running clearances, or “slip,” it is almost constant with varied speeds and flows, and it varies linearly as pressure changes.
When operating at higher speeds and outputs, changes in slip with pressure change typically have minimal influence on performance. Many viscous liquid pumping applications need adjustable flow independent of discharge pressure as well as pressure-independent volumetric efficiency. Some gear pumps have a pressure-compensating sealing device that may lower face and tip clearances, reducing internal leakage and increasing volumetric efficiency.
The sealing components are generally designed using a combination of theoretical predictions and practical experience. The geometry and designs of the seal should be optimized in phases. When a critical differential pressure is exceeded, the desired characteristics and an almost pressure-independent volumetric efficiency of roughly 74 to 88 percent can be reached, according to operational experience with gear pumps utilizing suitably designed pressure-compensating sealing components.
Liquid temperature, operating pressure, and pump speed may all impact friction torque and, as a result, pump operation and needed power in a gear pump. When the pressure differential is considerable, the friction torque first drops and then increases as the pump speed increases. In a low pump speed zone with a significant pressure difference, the friction torque may rise with an increase in liquid temperature, whereas in a high pump speed region, the friction torque may decrease.
When a gear pump has a low suction pressure (for example, when liquid is drawn from a lower-level tank), pressures in the suction piping and chamber approach vapor pressure, and cavitation can occur upstream from the gear meshing zone. In the event of transient operations, cavitation is another prevalent operational issue.
Insufficient flow into the growing inter-tooth volumes is a common source of cavitation. The inter-tooth books created at the roots of the driver and driven gears should be included in many theoretical or operational investigations on these issues. In cavitation and transient operation, compressible flow into and out of these compartments is critical.
TYPES OF GEAR PUMPS
Pumps that employ moving cogs or gears to convey fluids are known as gear pumps. The revolving element provides suction at the pump intake by forming a liquid seal with the pump casing. Fluid is pulled into the pump and encased in the cavities of its moving gears before being discharged. Gear pumps may be divided into two types.
External Gear Pump
An external gear pump is made up of two identical, interlocking gears that are held together by different shafts. In most cases, one gear is powered by a motor, which then drives the other gear. Motors may be used to drive both shafts in some instances. Bearings on each side of the casing support the shafts. When the gears come out of the mesh on the pump’s input side, they generate an enlarged volume.
As the gears continue to revolve against the pump casing, liquid pours into the cavities and is caught by the gear teeth. The trapped fluid is transported around the casing from the input to the discharge. As the gear teeth on the discharge side of the pump get entangled, the volume decreases and the fluid is forced out under pressure.
Internal Gear Pump
Internal gear pumps work on the same concept as external gear pumps, but the two interlocking gears are of different sizes, with one moving within the other. The bigger gear (the rotor) is an internal gear, which means its teeth protrude from the interior. A smaller external gear (the idler – just the rotor is driven) is positioned off-center within this.
This is intended to interlock with the rotor in such a way that the gear teeth engage at a single place. The idler is held in place by a pinion and bushing connected to the pump casing. A permanent crescent-shaped partition or spacer covers the vacuum left by the idler’s off-center mounting location and functions as a seal between the input and exit ports.
BENEFITS OF GEAR PUMPS
Gear pumps are small and basic, with only a few working components. They cannot equal the pressure produced by reciprocating pumps or the flow rates produced by centrifugal pumps, but they provide higher pressures and throughputs than vane or lobe pumps. Pumping oils and other high-viscosity fluids is a specialty for gear pumps. Because of the more robust shaft support and tighter tolerances, external gear pumps can withstand higher pressures and flow rates than internal gear pumps.
Gear pumps are often employed for metering and mixing activities since their output is precisely related to rotational speed. Gear pumps can be designed to handle corrosive liquids. While cast iron and stainless steel are typically used, new alloys and composites allow the pumps to handle corrosive liquids such as sulphuric acid, sodium hypochlorite, ferric chloride, and sodium hydroxide.
Kiron Hydraulic Needs, in association with Liquiflo Pumps, provides a comprehensive Gear pump system solution. Liquiflo Pumps has been a leading manufacturer of high-alloy gear pumps and centrifugal pumps since 1972, with products tailored to the chemical processing industry’s unique requirements. Liquiflo gear pumps have successfully handled thousands of tough chemicals in a variety of pumping circumstances, including high-viscosity, high-pressure, and high-temperature applications.