Comparison between Internal Gear Pump and External Gear Pump

1, the external gear pump flow displacement: V = πDhB = 2πm2zB In fact, the volume between the tooth space slightly larger than the tooth size, so usually take 3.33, then there: V = 6.66zm2B flow: q = Vnηv = 6.66 zm2Bnηv The above calculation is the average external gear pump flow. Features: 1) The average flow of the gear pump is proportional to the number of teeth, and proportional to the square of the modulus. 2) The flow of gear pump is proportional to tooth width, but the increase of tooth width is limited by the increased hydraulic radial force of gear. Generally, tooth width B = (6 ~ 10) m and small value at high pressure. 3) increasing the speed can increase the pump flow, but by the pump suction performance limits. Gear pump speed is generally 1000 ~ 1500r / min. 4) In addition, in the positive displacement hydraulic pump, the gear pump has the largest flow pulsation. 2, gear pump trapped oil phenomenon and the phenomenon of unloading trapped oil hazards: the pressure in the dead volume increased dramatically, the bearing is subject to a large additional load, while generating power loss and liquid fever and other undesirable phenomena; dissolved in The air in the liquid will precipitate bubbles, cavitation, causing vibration and noise. Eliminate the phenomenon of trapped oil: gear pumps in the side plate or open the unloaded trough on the sleeve. Asymmetrical, it must be ensured that the suction and pressure chambers can not be brought into direct contact with each other at all times; such gear pumps can not be reversed. 3, gear pump leakage and compensation measures gear pump there are three parts of the leak: the gear end face and the end cover; addendum and the housing and the gear between the hole at the mesh. Among them, the maximum leakage between the gear end face and the end cap accounted for 75 ~ 80% of the total leakage. 4, to improve the pressure of external gear pump measures End gap automatic compensation principle: the use of special channels to pressure gear oil pump pressure chamber leading to the outside of the floating sleeve, the role of a certain shape and size of the area, resulting in hydraulic Force, so that the sleeve pressed to the gear end face, the force must be greater than the role of the gear end face of the role of the sleeve in order to ensure that under a variety of pressures, the sleeve is always close to the gear surface automatically reduce the gear pump gear through the end face The leakage, to achieve the purpose of raising pressure. 5, the radial unbalanced damage: Radial unbalanced force can make the shaft bending, tooth top contact with the shell, while accelerating the wear and tear bearings, reducing bearing life. Measures: In order to reduce the influence of radial unbalance force, usually take the method of reducing the pressure port. Reduce the gear teeth, thus reducing the addendum diameter, bearing area decreases. Appropriate to increase the radial clearance. 6, Internal gear pump Internal gear pump with involute gear pump and cycloidal gear pump two. Cycloid gear pump, also known as the rotor pump, the two gears differ by a tooth. Gear pump is characterized by: small size, light weight, simple structure, easy manufacture, low price, reliable work, self-priming performance is better, not sensitive to oil pollution, easy maintenance. The disadvantage is: large flow and pressure pulsation, noise, displacement and other variables. Internal gear pump compared with the external gear pump, the main small, small flow pulsation, noise, etc., but the processing difficulties, the use is limited. Here the meshing point of the tooth surface contact line has been playing the role of high-pressure, low pressure chamber, so the gear pump does not need to set a special flow control mechanism.