DETERMINING THE CHARACTERISTICS OF PORTABLE PUMPS FROM THE CENTER USING AN EXPERIMENTAL SETUP

ABSTRACT

The article discusses the experimental determination of the characteristics of centrifugal pumps, which is essential for improving their efficiency in irrigation and water supply systems. The methods for measuring flow rate, head, and efficiency under various operating conditions are described, as well as the approaches to quantitative and qualitative control. The application of hydrodynamic curves and similarity laws is examined. Special attention is paid to accurate experimental planning, observation methods, and data analysis to obtain reliable results and reduce energy consumption.

АННОТАЦИЯ

В статье рассматривается экспериментальное определение характеристик центробежных насосов, что имеет важное значение для повышения их эффективности в системах орошения и водоснабжения. Описаны методы измерения расхода, напора и коэффициента полезного действия (КПД) при различных режимах работы, а также способы количественного и качественного регулирования. Рассматривается применение гидродинамических кривых и законов подобия. Особое внимание уделено точному планированию экспериментов, методам наблюдений и анализа данных с целью получения достоверных результатов и снижения энергозатрат.

Keywords: Experimental research setup, performance indicators, cavitation observation chamber, manometer, vacuum gauge, ultrasonic water flow meter.

Ключевые слова: Экспериментальная установка для проведения исследований, её рабочие характеристики, камера наблюдения за кавитацией, манометр, вакууметр, ультразвуковой расходомер воды.

INTRODUCTION

The experimental determination involves measuring key parameters such as flow rate, head, and power input under various operating conditions. These measurements allow for the calculation of pump efficiency and the plotting of performance curves, which are essential for evaluating and optimizing pump operation.

Additionally, the use of hydrodynamic similarity laws enables scaling of results from model tests to real-world applications, providing engineers with reliable data for designing and selecting pumps for specific irrigation needs. The chapter also highlights the importance of both qualitative and quantitative regulation methods in managing pump performance.

MATERIALS AND METHODS.

The collected data allows for the development of characteristic curves, which represent the relationship between key parameters such as flow rate, head, power consumption, and efficiency. These curves are instrumental in determining the most effective operating range of the pump and identifying potential areas of inefficiency.

Furthermore, the experimental approach enables the identification of deviations from theoretical performance due to factors such as mechanical losses, hydraulic resistance, and installation-specific variables. Such insights are critical for optimizing system design and ensuring long-term reliability and performance of pumping equipment.

In order to use pumps effectively under different conditions, information about their performance, i.e., their characteristics, must be provided. The pump characteristic refers to the set of graphs showing the relationships Н=f₁(Q), N=f₂(Q), h=f₃(Q, and Hvac=f4 (Q) when the rotational speed n=constn remains unchanged. Pump characteristics can be presented in specific, universal, or dimensionless forms. The form of the specific characteristics depends on the pump's specific speed coefficient n_s.

To determine the operating mode of a pump, the hydrodynamic curve of the pipeline in the Q-H coordinate system of the pump characteristic is constructed using the following formula:

;                                      (1)

or  ;                                  (2)

where,

;                       (3) 

R_т - is a constant value for a specific pipeline system, which depends on its dimensions and resistance coefficients.
For pipelines with a long length, it is allowed to consider the local head losses as approximately 10–15% of the head losses due to friction along the length, that is:

                                     (4)

Figure 1. Regulation of the Operating Mode of a Centrifugal Pump

a) Quantitative regulation;  b) Qualitative regulation.

The intersection point A between the pump’s pressure characteristic curve Н=f(Q) and the pipeline’s hydrodynamic curve Н_ТР=Н_г+R_ТQ² is referred to as the operating point (see Fig. 3.5a). Thus, when a given pump operates at a constant rotational speed n=const within a specific pipeline system, it develops a head Н_А, operates at an efficiency h_А, and is capable of lifting a fluid volume of Q_А to a height of Н_г. It is essential that the operating point A does not exceed the operational limit of the pump, i.e., the boundary of h=0,9 h_mах.

When adjusting the performance of a pump unit, quantitative and qualitative regulation methods are used.

RESULTS AND DISCUSSION

Quantitative regulation can be achieved by: a) Changing the position of the throttle valve on the pressure pipeline, b) Redirecting part of the flow from the pressure side back to the suction side, c) Trimming the outer diameter of the impeller in centrifugal pumps, d) Changing the blade angle in axial-flow pumps.

Table 1.

Table of the relationship between the updated pump's flow rate and pressure

Figure 2. Updated pump pressure characteristic

For example, when the rotation speed n=const, the pump discharge can be reduced from Q_с<Q_А by partially closing the throttle valve on the pressure pipeline.

In this case, the pump's Efficiency (η) decreases, meaning:

;                       (5)

Here, Н_с ,h_с are the head and efficiency of the pump corresponding to the reduced discharge Q_с (see Figure 1a).

h_кул is the pressure loss caused by the hydraulic resistance of the throttle valve.

Qualitative regulation Q_с of the pump unit's discharge is achieved by changing its rotation speed. To determine the rotational speed n_х that ensures the required liquid flow rate Q_с,

 the law of dynamic similarity is applied, and a proportionality curve is drawn (see Figure 1b).

Here, is the proportionality coefficient. The point E, which is the intersection of the proportionality curve with the pump's pressure characteristic curve , has coordinates Н_Е and Q_Е. Using these, the new rotational speed n_х is determined by the following formula:

                                          (6)

Here, n is the initial rotational speed of the pump. To recalculate the pump’s characteristics for the new rotational speed n_x, formulas (3.100), (3.101), (3.102), and (3.103) are used.

                                                 (7)

                                                   (8)

                                                 (9) 

                                                           (10)

Using this method, the pump's discharge can be increased or decreased, and it is much more efficient economically, because the pump's efficiency (η) does not change.

Moreover, to recalculate and construct the characteristics of a new prototype pump based on the characteristics of a model pump, the similarity laws for blade (impeller) pumps are applied, using equations (3.104), (3.105), and (3.106) [9].

                                   (11)

                             (12)

                             (13)

Here: , , , , and -  — are the discharge, head, power, impeller diameter, and rotational speed of the actual (prototype) pump; , , , , and  — are the discharge, head, power, impeller diameter, and rotational speed of the model pump.

Conclusion. The study confirms that experimental determination of centrifugal pump characteristics is not only necessary for evaluating performance but also for developing strategies to improve energy efficiency. The insights gained from the experiments serve as a foundation for optimizing pump selection, system design, and operational strategies in irrigation and water supply systems.

In addition, the results reinforce the need for continuous monitoring and periodic testing of pumps in real-world conditions to ensure they operate within their optimal performance range. This proactive approach contributes to extending equipment life, minimizing operational costs, and reducing the environmental impact of water pumping systems.

Ultimately, the integration of experimental data into the engineering decision-making process enhances the reliability and sustainability of hydraulic infrastructure.

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