Regarding stress, the following three concepts are often mentioned:
A. Working pressure: The output pressure of the hydraulic pump when it actually works is called working pressure. The working pressure depends on the size of the external load of the hydraulic system and the pressure loss on the drain line, and has nothing to do with the flow of the hydraulic pump.
B. Rated pressure: Under normal working conditions, the maximum pressure of the hydraulic pump for continuous operation according to the test standards. Normally, the working pressure shall not exceed the rated pressure. Generally, the rated pressure will be marked on the nameplate.
C. Maximum allowable pressure: The maximum pressure value that allows the hydraulic pump to operate for a short time under the condition of exceeding the rated pressure according to the test standards. Above this pressure, pump leakage will increase rapidly. The rated pressure must not exceed the maximum allowable pressure. Once exceeded, the pump will leak.
2. Displacement and flow
Cars often have 1.6 displacements and 2.0 displacements. This is actually the volume of gasoline consumed by one revolution of the engine, which is very similar to the displacement concept of a hydraulic pump.
Displacement refers to the volume of oil that can be discharged by the hydraulic pump in one revolution without leakage. This is a parameter related to the mechanical structure of the hydraulic pump. Its size is only related to the geometry of the sealed working cavity in the hydraulic pump The size is related to the number.
In terms of mechanical structure, some displacements are constant, namely fixed pumps, and some displacements are variable, namely variable pumps.
Note: Generally, quantitative pumps have better sealing performance, less leakage, and higher efficiency at high pressure.
The flow is the volume of liquid discharged by the pump per unit time (L/min), with theoretical flow Qth, actual flow Qac, and rated flow Qn
Theoretical flow refers to the flow value obtained without considering the leakage, so Qth=qn, where q is the pump displacement (L/r) and n is the pump speed (r/min)
The actual flow takes into account this part of the leakage, Qac=Qth-△Q, where △Q represents the leakage loss of the pump, and the oil will leak from the high pressure area to the low pressure area when the pump is running
The rated flow Qn (L/min) refers to the flow rate that the hydraulic pump must guarantee under normal working conditions according to the test standard (such as at the rated pressure and rated speed). It is usually marked on the nameplate. In theory, the output flow will be slightly lower than the rated flow value.
3. Power and efficiency
When we choose a hydraulic pump, we must inevitably consider the power of the pump and whether the efficiency can meet the requirements. At this time, we need to calculate. Some formulas involved are as follows
Post time: Nov-13-2020