In terms of their operating chamber and its connection with the pump inlet and discharge, gear hydraulic machines shall be classified as the volumetric equipment. Similar to all other types of volumetric rotor hydraulic machines, gear-type hydraulic machines can operate in two reverse modes: the pump mode and the hydraulic motor mode. A gear hydraulic machine operates as a pump when the rotary moment is applied to the shaft. If, instead, the rotary moment is taken off from the shaft, and liquid driven by pressure is delivered to the machine inlet, the machine runs as a hydraulic motor.
A gear pump consists of two gears engaging each other and mounted in the pump casing with small gaps. One gear is a drive gear, another is a driven gear. When gears rotate, operating liquid flows between the teeth and becomes separated from the suction line and the discharge line; subsequently, teeth displace liquid in to the discharge line.
Gear pumps are classified into three major types according to the gear engagement.
1. Externally engaged gear pumps
This type of gear pumps is the most common and simple. Forced displacement is driven by variation of volumes in cavities between the engaged gears rotated by independent drives. This pump is a powerful and low-cost solution. As a rule, gear pumps are used to move highly-viscous liquids free of inclusions. As compared with internally engaged pumps, externally engaged pumps can operate under much higher pressures; however, their sizes are larger.
2. Internally engaged gear pumps
This type of gear pumps is a modification with the driven gear installed inside the drive gear having larger diameter; the driven gear rests on a crescent-shaped part made of steel. When gears rotate, this structure provides higher displacement volume; as a result, the internally engaged gear pumps, when filled, demonstrates the suction effect.
3. Three-gear pumps
These pumps include one drive gear and two driven gears, 4 suction cavities and 5 discharge cavities. These pumps are effective for application in hydraulic drives where two independent hydraulic discharge lines are required. Число зубьев и угол зацепления напрямую влияет на равномерность подачи жидкости. Чем больше зубьев, тем равномернее подача, но меньше производительность. В боковых стенках корпуса насоса есть разгрузочные канавки, по которым жидкость отводится в одну из полостей, в следствие чего жидкость не защемляется в зоне контакта зубьев шестерен.
For this type of pumps, casings are made of aluminium alloy; inside the casing is the bearing unit, with the drive gear and the driven gear, and the sealing unit.
Two segmented surfaces in the center of the sealing unit envelop the teeth, making the specified gap; these surfaces are used to seal the gears radially. Two pressing plates inserted into specially prepared grooves in the sealing unit, at two sides of gears, are used as end seals. Recesses for rubber gaskets are available in the left part of the sealing unit and in the pressing plates. Liquid from the discharge cavity presses the plates, abutting them against the gears’ edges; as a result, the gap is compensated, and leakages become equal irrespective of the pump operating pressure. The gears, both the drive one and the driven one, are made integral with pins resting on the plain bearings in the sealing unit and the bearing unit. The pump is covered with the cap sealed by the rubber O-ring. The drive shaft in a gear pump is sealed by the rubber collar fastened by special rings in the pump casing.
A gear pump includes two gears placed in the casing. One gear is activated by the electric motor installed on the axis; another gear is rotated due to tight engagement of teeth. During operation, gear teeth capture liquid, press it towards the casing walls and move it to the discharge side, away from the suction side. Due to the tight engagement of teeth, operating liquid backward flow is practically impossible.
The number of teeth may be reduced to two; however, in such a case, the outlines of rotary elements will be similar to the figure-of-eight.
In chargers of this type, the driving operation must be provided from the motor of both elements, because they are not engaged, unlike the gear wheel pumps.
In terms of displacement principle, gear pumps shall be classified as rotor-type rotary machines; they are common specimens of rotor hydraulic machines with gears wheels used as displacers. In these pumps, displaced liquid moves in the plane that is perpendicular to the rotation axis; as a result, liquid is transferred from the suction cavity to the discharge cavity. The movements of displacers are rotary only.
Externally engaged gear pumps are the most common. Such pump includes two identical cylindrical gears: one of these gears is operated as the drive gear, and another, as a driven gear. Both gears are in the tight casing (the stator). While the gears rotate, liquid, that fills the recesses in teeth, is pumped from the suction cavity to the discharge cavity. The design of externally engaged gear pumps is simple while reliable; also, these pumps are light-weight.
Internally engaged gear pumps are small-sized but their design is difficult for manufacturing.
If need exists to increase the discharge, three-gear pumps or pumps with larger numbers of gears are used. In these pumps, gears are mounted around the central drive gear. To increase the operating liquid pressure, multistage gear pumps are used. In these pumps, the discharge at each stage is less than at the previous one. The bypass valve is used to remove the excessive liquid.
Gear pumps are widely used in a great variety of industries due to their several advantages over other pump types. The major advantages include reliability, small sizes, simple design and relatively high efficiency. Also, gear pumps contain no operating elements affected by centrifugal forces; as a result, these pumps are operable at RPM 20 s-1. Also, gear pumps can produce high pressure, pump viscous and hot substances, and reverse the pumping direction.
The advantages of this type of chargers are as follows: the design is simple and small-sized; no valves used; high-speed electric motors can be used as drive motors; reversibility; high pressure can be produced (5 MPa for gear pumps, 0.5 MPa for figure-of-eight type pipes).
We are convinced that our company ENCE GmbH will become your reliable and efficient distributor (authorized representative) of your gear pumps in the Russian market.
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