PROCEDURES

Preliminaries

 

               i.      We were being adequately supervised.

             ii.      The pump discharge valve and suction valves is turned to fully open and motor speed being controlled control to zero.

            iii.      The electrical supply and motor drive switch is turned. Motor control knob being slowly adjusted to around half way position. Any possible leaks in the system being checked as well as all gauges etc. The motor speed being reduced back to zero. The apparatus is ready for tested.

 

 

Actual Experiment

               i.      The suction valve is opened and discharge valve being closed. Maximum pump speed N1 is taken by adjusting speed control to 100%.

             ii.      Discharge valve is fully opened and water is allowed to circulate. Note the volume of the flow indicated and suitable increments in flow is decided to give adequate sample point (about 10 points from zero until maximum flow).

            iii.      The discharge valve being closed (corresponding to no flow). All the measurements being taken when the measured readings are steady.

           iv.       To give the first increment in volume flow, the discharge valve being opened slightly. Measurements being taken when readings are steady.

             v.      Step (iv) is repeated. When the valve being fully open consider it as the final measurement.

           vi.      The entire experiment being repeated at pump speed correspond to speed control position of 75% and 50%. 

OBJECTIVES

The objective of this experiment is to obtain performance characteristics (as describe above) for a variable speed centrifugal pump operating at 3 different impeller speeds.

 

EXPERIMENTAL APPARATUS

 

The experimental set-up consists of;

i)                    Water flow bench and centrifugal pump

ii)                   Instrumentation for data acquisition

 

Instrument Panel – Refer to the schematic diagram below.

i)                    Speed control to change the pump speed. Pump speed can be varied over range of 0 – 3000 rpm.

ii)                   Pump suction and delivery pressures.

iii)                 Torque measurement.

Figure 1.3 The Instrument Panel.

TURBINE INLET

TORQUE (Nm)

PUMP DELIVER

PUMP SUCTION

MOTOR DRIVE

	Figure 1: Schematic of Instrument Panel

 

 

Flow Measurement – Using “V” notch weir

Flow rate in the system can be measured relating the height of water seen in the sight glass to graph T1 and reading off the flow rate in litres per minute.

 

Figure 1.4 The ‘V’ Notch Weir.

 

Speed Measurement

Pump motor speed measurements are made using hand held digital tachometer

THEORY

One of the most common radial-flow turbo machines in the centrifugal pump. This type of pump has two main components: an impeller attached to a rotating shaft, and a stationary casting (or housing) enclosing the impeller. Schematic diagram of basic elements of centrifugal pump is as shown below.

 

Consider the experimental arrangement for determining the head rise (or pressure rise) gained by fluid flowing through a pump, as shown in figure below.

 

			Impeller

 

 

 

Eye

Inflow

Blade

Hub plate

	Casing, housing or volute

 

 

 

Figure 1: Basic Elements of Centrifugal Pump

 

 

Figure 1.1 Experimental Arrangements for Pump Performance Characteristic.

 

 

 

The pump head rise can be expressed using the energy equation as,

           

Typically the differences in elevations and velocities (between inlet and outlet) are so small that,

           

The power,

The pump overall efficiency, is the ratio of power actually gained by the fluid to the shaft power supplied () as given by the equation,

 

 

Figure 1.2 The Motor of the Centrifugal Pump

THEORY

One of the most common radial-flow turbo machines in the centrifugal pump. This type of pump has two main components: an impeller attached to a rotating shaft, and a stationary casting (or housing) enclosing the impeller. Schematic diagram of basic elements of centrifugal pump is as shown below.

 

Consider the experimental arrangement for determining the head rise (or pressure rise) gained by fluid flowing through a pump, as shown in figure below.

 

			Impeller

 

 

 

Eye

Inflow

Blade

Hub plate

	Casing, housing or volute

 

 

 

Figure 1: Basic Elements of Centrifugal Pump

 

 

Figure 1.1 Experimental Arrangements for Pump Performance Characteristic.

 

 

 

The pump head rise can be expressed using the energy equation as,

           

Typically the differences in elevations and velocities (between inlet and outlet) are so small that,

           

The power,

The pump overall efficiency, is the ratio of power actually gained by the fluid to the shaft power supplied () as given by the equation,

 

 

Figure 1.2 The Motor of the Centrifugal Pump

Centrifugal Pump Performance Characteristic

INTRODUCTION

A positive displacement pump emits a given volume of fluid for each revolution of the motor. Bellows, double-diaphragm, flexible impeller, gear, oscillating, piston, progressing cavity, rotary lobe, rotary vane, and peristaltic pumps are all positive displacement pumps.

 

Centrifugal Pump Fundamentals

 

Pump Characteristic Curves

The performance of a centrifugal pump can be shown graphically on a characteristic curve. A typical characteristic curve shows the total dynamic head, brake horsepower, efficiency, and net positive Suction head all plotted over the capacity range of the pump.

Dimensional curves which indicate the general shape of the characteristic curves for the various types of pumps. They show the head, brake horsepower, and efficiency plotted as a percent of their values at the design or best efficiency point of the pump.

Figure below shows that the head curve for a radial flow pump is relatively flat and that the head decreases gradually as the flow increases. Note that the brake horsepower increases gradually over the flow range with the maximum normally at the point of maximum flow.

Fig. Radial Flow Pump

Figure 1.0 The Centrifugal Pump Tank.