# How to choose hydraulic system components?

Date:25 Sep 2020
Summary:

Determination of hydraulic pump and calculation of requ […]

Determination of hydraulic pump and calculation of required power 1. Determination of hydraulic pump (1) Determine the maximum working pressure of the hydraulic pump. The determination of the required working pressure of the hydraulic pump is mainly based on the maximum pressure p1 required by the hydraulic cylinder at each stage of the working cycle, plus the total pressure loss ΣΔp from the oil pump outlet to the cylinder oil inlet, that is, pB=p1+ΣΔpΣΔp Including the local pressure loss of the oil flowing through the flow valve and other components, the loss along the pipeline, etc., before the system pipeline is designed, it can be estimated based on the experience of similar systems, the general simple pipeline throttle valve speed control system? ΣΔp It is (2～5)×105Pa, and the system ΣΔp with speed control valve and complicated pipeline is (5～15)×105Pa, ΣΔp can also consider only the pressure loss flowing through each control valve, and the piping system The process loss is negligible. The rated pressure loss of each valve can be found in the hydraulic component manual or product catalog, or can be selected by referring to the following table. Pressure loss (Δpn) of commonly used medium and low pressure valves

(2) Determine the flow rate qB of the hydraulic pump. The pump flow rate qB is determined according to the maximum flow rate qmax required by the actuator action cycle and the leakage of the system.
①When multiple hydraulic cylinders act at the same time, the flow of the hydraulic pump should be greater than the maximum flow required by several hydraulic cylinders (or motors) that act at the same time, and the leakage of the system and the decrease in volumetric efficiency after the wear of the hydraulic pump should be considered, that is, qB≥ K(Σq)max(m3/s) where: K is the system leakage coefficient, generally 1.1～1.3, the large flow rate is the small value, and the small flow rate is the large value; (Σq)max is the hydraulic cylinder (or motor) acting simultaneously ) Maximum total flow (m3/s).
②When using a differential hydraulic cylinder circuit, the required flow rate of the hydraulic pump is: qB≥K(A1-A2)vmax(m3/s) where: A 1, A 2 are the rodless cavity and rod cavity of the hydraulic cylinder respectively The effective area (m2); vmax is the maximum moving speed of the piston (m/s).
③When the system uses an accumulator, the hydraulic pump flow is selected according to the average flow of the system in a cycle, that is, qB= ViK/Ti where: Vi is the total oil consumption of the hydraulic cylinder in the working cycle (m3); Ti is the working cycle of the machine (s); Z is the number of hydraulic cylinders.

(3) Select the specifications of the hydraulic pump: According to the maximum pressure pB and flow qB calculated above, check the product samples of hydraulic components, and select the specifications of hydraulic pumps equivalent to PB and qB. The maximum pressure pB calculated above is the static pressure of the system. There is a dynamic pressure in the transition process during the working process of the system, and the dynamic pressure is often much higher than the static pressure, so the rated pressure pB of the pump should be 25% larger than the maximum pressure of the system~ 60%, so that the hydraulic pump has a certain pressure reserve. If the system is in the high-pressure range, the pressure reserve takes a small value; if the system is in the medium-low-pressure range, the pressure reserve takes a large value.

(4) Determine the power to drive the hydraulic pump.
①When the pressure and flow of the hydraulic pump are relatively equal, the required power is: p=pBqB/103ηB (kW) where: pB is the maximum working pressure of the hydraulic pump (N/m2); qB is the flow of the hydraulic pump (m3) /s); ηB is the total efficiency of the hydraulic pump. The total efficiency of various types of hydraulic pumps can be estimated by referring to the following table. For hydraulic pumps with large specifications, the larger value is used, otherwise the smaller value is used. Small value.
②In the working cycle, when the pressure and flow of the pump change significantly, the driving power required for each stage in the working cycle can be calculated separately, and then the average formula: t1, t2,..., tn is a working cycle The time required for each stage (s); P1, P2,..., Pn are the power (kW) required by each stage in a working cycle. According to the above-mentioned power and pump speed, a standard motor can be selected from the product sample, and then checked, so that when the motor emits maximum power, its overload is within the allowable range.More about:hydraulic fittings manufacturers

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