Method for measuring output flow of hydraulic pump with clamp type ammeter

Method for measuring the output flow of hydraulic pump with clamp-type ammeter Zhu Baojing (Jinan Yuyin Zhongyuan Hydraulic Parts Factory, No. 303, Jing 10 Road, Jinan, Shandong Province, China) 250021 Tel: 013806495 Except for the special hydraulic component test bench, all hydraulic systems have no special requirements. In the case of a flow meter that does not detect the output of the hydraulic pump, in some cases, the design and maintenance personnel must also know the output flow of the hydraulic pump in the system. This paper focuses on the case where the hydraulic pump is directly driven by the motor in the hydraulic system. The method of calculating the output flow of the hydraulic pump by measuring the running current of the three-phase asynchronous motor with a clamp-type ammeter is emphasized.

It is well known that in the hydraulic system that directly drives the hydraulic pump with a motor, the driving power required by the hydraulic pump is the actual output power of the motor. The larger the output flow of the hydraulic pump and the higher the pressure, the greater the actual output power of the motor required. That is to say, when the motor is operated at the rated voltage, the actual running current of the motor required is also larger. It can be seen that there is a certain relationship between the output flow of the hydraulic pump and the running current of the motor.

The actual driving power required by the hydraulic pump: where N is the input power of the hydraulic pump (kW) - the working pressure of the hydraulic pump (M Pa) - the actual output flow of the hydraulic pump (L / min) Z - the hydraulic pump The total efficiency of the hydraulic pump is equal to the product of the volumetric efficiency of the hydraulic pump and its mechanical efficiency. Different types of hydraulic pumps have different Z values. For specific data, refer to Table 1. The hydraulic pump specifications take large values ​​and the specifications are smaller.

When the working pressure of the hydraulic pump is lower than its rated pressure and the working flow is less than its nominal flow rate, its total efficiency will decrease.

Gear pump single-acting vane pump double-acting vane pump screw pump radial piston pump axial piston pump. Under the rated voltage, the relationship between the actual output power of the three-phase asynchronous motor and the load operating current is as follows: ―Motor actual output power (kW)——Motor rated power (kW)——Motor running current (A)——Motor rated current (A)——Motor no-load current (A) According to the above analysis: Hydraulic pump is motor Direct drive, and the motor works at rated voltage N = P, the relationship between the actual output flow Q of the hydraulic pump and the motor running current I is obtained by the formula (1), (2): it can be detected from the motor nameplate , I can be measured by the clamp current meter on site, p can be read from the hydraulic station pressure gauge, Z can check the manual of the hydraulic pump, also refer to Table 1.

Type (3) is very useful for design and maintenance personnel. For example, when I was repairing a 25SCY141B manual variable displacement piston pump, I accidentally lost its flow indicator. I only know that the actual output flow rate set by the plunger pump in the system is 18 L / min and the working pressure is 20 M. Pa, and is directly driven by a 4-pole 7.5 kW three-phase asynchronous motor, and no flow meter is installed in the system. It is difficult to re-adjust the pump flow in this case, but the pump can be calculated at 20 M under the condition that the pump (P) is pre-measured with the no-load current of the pump drive motor = 6 A. Pa, flow rate 18 L / min, the motor running current at rated voltage I = 14. 6 A. So after replacing the repair pump, first adjust its output flow to a minimum, at a pressure of 20 M Pa, slowly Increase the flow rate of the pump, and measure the running current of the motor with a clamp-type ammeter. When the value of the clamp meter indicates that the value is stable at 14.6 A, the actual output flow rate set by the pump is 18 L / min. After adjustment, the actuator speed in the system is exactly the same.

This article does not introduce much more about the case where the motor is not operating at rated voltage and the motor does not directly drive the hydraulic pump.

[1] Zhang Lei et al. Practical hydraulic technology 300 questions. Beijing: Mechanical Industry Press, Lei Tianjue. Hydraulic Engineering Manual. Beijing: Mechanical Industry Press, 1990, 4.

[3] Wang Rugui. Practical electrician calculates 150 cases. Beijing: People's Posts and Telecommunications Press,