Created on：2021-05-21 08:59

# Performance parameters of axial piston pump

Performance parameters of axial piston pump

The main performance of axial piston pump includes pressure, displacement, speed, efficiency and service life. The main structural parameters include plunger diameter, plunger number, swash plate angle, etc.

(l) Pressure in all kinds of hydraulic pumps, the plunger pump can achieve the highest t working pressure. The pressure of straight axis and inclined axis plunger pump generally reaches 40 ~ 48mpa, and some military products even reach 60MPa; the maximum pressure of rotary swash plate plunger pump reaches 100MPa.

(2) The displacement of the axial piston pump mainly depends on the diameter of the plunger, the effective stroke of the plunger, the inclination angle of the swash plate (the angle between the transmission shaft and the cylinder axis) and the number of times of action of each plunger in each working cycle.

The general calculation formula of displacement of plunger pump is

V=Kπ/4d2hZ×10-3 (mL/r) (4-1)

Where K -- the number of action of each plunger in each working cycle;

D -- plunger diameter, mm;

H -- effective stroke of plunger, mm;

Z -- number of plunger.

The displacement calculation formula of axial piston pump is shown in the table below.

Calculation formula of axial piston pump displacement

 type 排量（mL/r）计算式 说 明 直轴式柱塞泵 V=π/4d2ZDtanγ×10-3 d-柱塞直径，mm；Z-柱塞数；D-柱塞分布圆直径，mm；γ-斜盘倾角，（°） 斜轴式柱塞泵 V=π/4d2ZDsinγ×10-3 d-柱塞直径，mm；Z-柱塞数；D-传动轴驱动盘上连杆球窝的分布圆直径，mm；γ-传动轴与缸体轴线之间的夹角，（°）

The displacement range of common straight shaft piston pump is 1.5 ~ 1500ml / R; the displacement range of inclined shaft piston pump is 5 ~ 2500ml / R; the displacement range of swashplate piston pump is 2.5 ~ 100ml / R.

(3) The allowable speed of rotary piston pump is very high, and the specific value varies with the displacement specifications. For example, the speed of small displacement pump can exceed 10000 R / min, the speed of medium displacement pump is 3000 ~ 5000 R / min, and the speed of large-scale heavy series straight shaft pump can reach more than 2000 R / min under the condition of preloading.

(4) Efficiency among all kinds of known hydraulic pumps, the working volume of plunger pump has completely continuous sealing line (surface), so it can achieve the highest volumetric efficiency. Because of the good lubrication condition between the moving pairs, its mechanical efficiency has reached a very high level. At present, the volumetric efficiency and mechanical efficiency of 40 MPa heavy series axial piston pump near the rated operating point are more than 95%, and the highest total efficiency is 91% ~ 93%. Because the swing angle of the cylinder body of the inclined shaft piston pump can be larger, the "dead volume" in the working volume is relatively small, and there is no leakage item of the slipper hydrostatic bearing. In addition, the stress condition of the cylinder body and the plunger is better, its volumetric efficiency and Mechanical efficiency will be higher than that of the straight shaft piston pump of the same grade.

Because of leakage and friction, the total efficiency curve obtained by multiplying volumetric efficiency and mechanical efficiency shows a trend of first increasing and then decreasing with the increase of pressure and speed. Due to the influence of the support stiffness of the variable displacement mechanism, the efficiency of the variable displacement pump is always slightly lower than that of the constant displacement pump. In addition, the efficiency of the hydraulic pump has a great relationship with the character, quality and temperature of the working medium.

Figure P shows the total characteristic efficiency curve of a typical inclined shaft quantitative piston pump.

(5) Service life the friction pairs of the main working parts of modern piston pump generally have a good liquid lubrication layer. Some of them are designed based on the principle of Keding hydrostatic bearing, and all of them are made of high-performance materials and undergo fine processing and heat treatment. Therefore, under the correct use conditions (especially the working medium with appropriate viscosity is used and its sufficient cleanliness is maintained), the piston pump is easy to operate Under rated t condition, the service life is very long, for example, for heavy series axial piston pump, it can reach more than 10000 ~ 12000h. Generally speaking, the service life of axial piston pump is longer than that of radial piston pump, and the rotary cylinder pump is longer than the swashplate pump in the straight axis piston pump.

(6) Compared with other hydraulic pumps, the flow pulsation and noise of plunger pump are larger. The flow pulsation of piston pump is the main cause of noise. Among all kinds of piston pumps, the noise level of seat valve piston pump is the highest, while that of other piston pumps is almost the same. The number of plunger has a great influence on the flow pulsation, and the odd number of plunger is better than the even number to reduce the flow pulsation. For this reason, the traditional design criterion is to take the number of plunger as odd, that is, 5, 7, 9, 11, etc.

(7) Power density and cost performance the high pressure, high speed and wide range of working envelope of plunger pump enable it to transmit a large power value. The power density in the high pressure system can reach more than 10kW / kg, especially as a high pressure variable pump, it has high cost performance, which can not be replaced by other types of pumps. However, because it is a kind of non pressure bearing shell element, the displacement value per unit structure volume is not as large as that of gear pump and vane pump, so the plunger pump is bulky and expensive in medium and low pressure hydraulic system and as a quantitative pump.

(8) The main structural parameters Z, D and R are three mutually restricted parameters, which are related to the structural type, performance, strength, rigidity and processability. When the number of plunger is large, the displacement of axial piston pump can be increased, but if the number of plunger is too large, the radial size of the pump and the volume and weight of the whole pump will be increased. In order to reduce the flow pulsation, the number of plunger in plunger pump should be odd, usually z = 5 ~ 9, z = 9 for through shaft plunger pump and z = 7 for non through shaft plunger pump.

The inclination angle of swash plate of straight shaft piston pump is generally from 18 ° to 21 ℃. The angle between transmission shaft and cylinder axis of inclined shaft piston pump is usually γ max = 25 ° to 45 °.

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