Lab 3 Pump Characteristics

Memoradum

Abstract 

This lab will experimentally determine the behaviors of centrifugal and positive displacement pumps. Specifically, the pump performance curves, which contain information about the pump’s efficiencies and flowrates, for each type of pumps will be created. Students will measure the actual head rise caused by the pump under 5 different flowrates. Based on the calculations carried out below, the centrifugal pumps are most appropriate for projects that require high head rise with low flow, the positive displacement pumps are most suitable for projects that require high flow with low head rise.

Introduction

        The purpose of this lab is to examine the behaviors of centrifugal and positive displacement pumps. Centrifugal pumps are the more widely used out the two pumpes in moving fluid through pipes. Centrifugal pumps operate by creating a centrifugal force on the fluid through the movement of the vanes.

        Using Bernoulli’s Equation, the actual head rese (ha) of fluid caused by the pump can determined. Assuming constant pipe cross section and negligible change in pipe elevation, the head rise can be approximately as:

[pic 1]

Where point 2 is measured right before the pump and point 3 right after the pump.

From the head rise equation, the power gained by the fluid can be calculated as:

[pic 2]

The water horsepower for valve position and normalize to the maximum water horsepower measured will approximate pump efficiency:

                                                                                                                                       (Equation 3)[pic 3]

In this experiment, the shutoff head condition is not tested for each pump.

Method         

Part I: Positive Dsplacement

The downstream and upstream values were turned opened, the difference in elevation of the reservoir surface, the center of the pump, and the height of the pressure gate were recorded. Two speed were used in this part, and the flowrates were recorded by collecting water in amount of time. The flowrate and pressure gage readings were taken for 5 trails under each speed.

 Part II: Centrifugal pumps

Part II was similar as Part I, but only one speed mode was used for big centrifugal pump, the upstream and downstream pressure gages were used to obtain the pressure readings, which later were used to calculate the actual head rise. The flowrate was adjusted by adjusting the valve downstream of the pump.

Results

Volume, time, gage pressure and speed had been recorded, so the flowrate, head rise, power and efficiency can be calculated for each pump. Table 1 and table 2 were the results of centrifugal pumps, table 3 was the results of positive displacement. Table 5 was the free delivery estimates table. Figure 1 was Pump performance curve for big centrifugal pump, Figure 1 also included the plot of question 4 (textbook example 12.4), Figure 2 and 3 were the pump curve for small centrifugal, Figure 4 and 5 were the pump curve for ear pump.

Table 5, 6 and 7 in Appendix showed the dimension measurements of each pump. Example calculations and calculation of Question 4 were attached in the appendix.

Table 1: Results for Big centrifugal pump

[pic 4]

Table 2: Results for Small centrifugal pump (high and low speeds)

[pic 5]

Table 3: Results for Positive displacement (high and low speeds)

[pic 6]

Table 4: Free delivery estimates