Part 3_single-stage Piston Compressor

Experiment Instructions ET 513

Single-stage piston compressor

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

Experiment Instructions

Last modification by: Heike Grünewald

This manual must be kept by the unit. Before operating the unit: - Read this manual. - All participants must be instructed on handling of the unit and, where appropriate, on the necessary safety precautions.

Version 0.1

Subject to technical alterations

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

Table of Contents 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2

Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.1 Intended use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2.2 Structure of safety instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

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2.3 Safety instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.4 Ambient conditions for the operating and storage location . . . . . . . . . 5 3

Description of the device . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1 Device design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3.2 Process schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 3.3.1

Pressure switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3.2

Pressure sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.3.3

Manometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.3.4

Safety valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.3.5

Non-return valve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.4 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.5 Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.6 Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.7 Measurement data acquisition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.7.1

Installing the software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.7.2

Program operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.8 Care and maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

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SINGLE-STAGE PISTON COMPRESSOR

Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 4.1 Use of a compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.2 Function of a compressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

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4.3 Characteristic variables of the piston compressor. . . . . . . . . . . . . . . 25

5

4.3.1

Characteristic curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.3.2

Isothermal efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.3.3

Volumetric efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.3.4

Pressure ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

4.3.5

Measuring the volumetric flow rate using a Venturi nozzle (differential pressure sensor) . . . . . . . . . . . . . . . . . . . . . . . . 29

Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 5.1 Series of measurements 1: Operating the compressor at constant speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.1.1

Objective of the experiment . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.1.2

Preparation for the experiment . . . . . . . . . . . . . . . . . . . . . . . 31

5.1.3

Conducting the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . 32

5.1.4

Measured values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.1.5

Analysis of the experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5.1.6

Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

5.2 Series of measurements 2: Operating the compressor at constant pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.2.1

Objective of the experiment . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.2.2

Preparation for the experiment . . . . . . . . . . . . . . . . . . . . . . . 37

5.2.3

Conducting the experiment. . . . . . . . . . . . . . . . . . . . . . . . . . 38

5.2.4

Measured values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

5.2.5

Analysis of the experiment . . . . . . . . . . . . . . . . . . . . . . . . . . 40

5.2.6

Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5.3 Consideration of both measurement series. . . . . . . . . . . . . . . . . . . . 43

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SINGLE-STAGE PISTON COMPRESSOR

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.1 Technical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.2 List of formula symbols and units . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6.3 Tables and graphs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

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6.4 Worksheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 6.4.1

Worksheet 1: Measured values . . . . . . . . . . . . . . . . . . . . . . 50

6.4.2

Worksheet 2: Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . 51

6.4.3

Worksheet 3: Isothermal efficiency over pressure ratio . . . . 52

6.4.4

Worksheet 4: Volumetric efficiency over pressure ratio . . . . 53

6.4.5

Worksheet 5: Efficiency over compressor speed . . . . . . . . . 54

6.4.6

Worksheet 6: Volumetric efficiency over compressor speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

6.4.7

Worksheet 7: Heating ratio over pressure ratio . . . . . . . . . . 56

6.4.8

Worksheet 8: Compressor characteristic volumetric flow rate over compressor speed . . . . . . . . . . . . . . . . . . . . . 57

6.4.9

Worksheet 9: Compressor characteristic pressure difference over volumetric flow rate . . . . . . . . . . . . . . . . . . . 58

6.4.10 Worksheet 10: Compressor characteristic volumetric flow rate over pressure difference . . . . . . . . . . . . . . . . . . . . 59

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SINGLE-STAGE PISTON COMPRESSOR

Introduction

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To generate compressed air for industry and commerce, in which compressed air is used as an energy source, equipment known as compressed air generating systems are used. A central component of these systems is the compressor. It is responsible for increasing the air pressure by means of mechanical energy. Compressed air generating systems are used to drive machinery in mining, for pneumatic controllers in assembly plants or to inflate tyres at petrol stations.

The ET 513 Single-stage piston compressor, together with the HM 365 Universal brake and drive unit, forms a complete compressed air generating system.

The trainer is suitable for both practical training in vocational schools and for laboratory experiments at colleges and universities.

Learning objectives • Design and operating behaviour of a compressed air generation plant with single-stage piston compressor • Determining the characteristic curve • Determining the volumetric efficiency • Determining the isothermal efficiency

1 Introduction

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

2

Safety

2.1

Intended use The unit is to be used only for teaching purposes.

2.2

Structure of safety instructions

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The signal words DANGER, WARNING or CAUTION indicate the probability and potential severity of injury. An additional symbol indicates the nature of the hazard or a required action.

Signal word

DANGER

Indicates a situation which, if not avoided, will result in death or serious injury.

WARNING

Indicates a situation which, if not avoided, may result in death or serious injury.

CAUTION

Indicates a situation which, if not avoided, may result in minor or moderately serious injury.

NOTICE

2 Safety

Explanation

Indicates a situation which may result in damage to equipment, or provides instructions on operation of the equipment.

2

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Symbol

Explanation Electrical voltage

Hazard area (general)

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Hot surface

Rotating parts

Wear ear defenders

Notice

2 Safety

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ET 513

2.3

SINGLE-STAGE PISTON COMPRESSOR

Safety instructions Also observe the operating instructions for the HM 365 Universal brake and drive unit and the safety instructions specified therein.

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WARNING Electrical connections are exposed when the switch cabinet is open. Risk of electrical shock. • Before opening the switch cabinet: pull the plug out. • All work must be performed by trained electricians only. • Protect the switch cabinet from moisture.

WARNING Rotating V-belt. Risk of hand injuries. • Do not touch the V-belt during operation.

WARNING Noise emissions up to 90dB(A). Risk of hearing damage. • Wear ear protectors.

2 Safety

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

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CAUTION Hot components. Risk of burns. • Allow the plant to cool down before touching.

NOTICE Possibility of damage to the compressor. • Do not exceed the rated speed of 980min-1 during experiments with variable speed.

2.4

Ambient conditions for the operating and storage location • Enclosed space. • Free from dirt and humidity. • Level and fixed surface. • Frost-free.

2 Safety

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ET 513

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SINGLE-STAGE PISTON COMPRESSOR

Description of the device

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In addition to the ET 513 Single-stage piston compressor, a functional experimental setup also includes the HM 365 Universal brake and drive unit. The drive unit is coupled to the trainer; the electric motor on the drive unit then drives the compressor via a V-belt. The speed and torque of the driving motor can be read off from the drive unit. The trainer consists of a single-stage piston compressor. Relevant measured values are recorded while this compressor is operated. These are displayed digitally and simultaneously transmitted to a PC. HM 365 Universal drive and brake unit

Fig. 3.1

ET 513 Singlestage piston compressor

They are available on the PC for further processing in a software program.

The compressor has one cylinder and is therefore single-stage. Its rated speed is 980min-1. At a positive operating pressure of 8bar, the compresFunctional experimental setup sor delivers 105 litres of air per minute.

3 Description of the device

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ET 513

3.1

SINGLE-STAGE PISTON COMPRESSOR

Device design

9 10

8

11 12

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Suction line

7 6 5

13 14 4

15 16

3 2 Pressure line

17 18 19

1

20 21

22 1 2 3 4 5 6 7 8 9 10 11 12

Pressure vessel Pressure sensor Manometer for delivery pressure Pressure switch Main switch Switch for solenoid valve Pressure drop signal lamp Switch cabinet Temperature sensor for supply line Compressor Temperature sensor for suction line V-belt pulley

Fig. 3.2

23 B2 P02 P02 PSH

T02 V1 T01

13 14 15 16 17 18 19 20 21 22 23

Sound absorber Solenoid valve Non-return valve Safety valve Manometer for intake pressure Pressure sensor Intake valve Differential pressure sensor Intake vessel Blow-off valve Sound absorber

X2 V01 V04 V07 P01 P01 V02 PD03 B1 V03 X1

Structure of ET 513 (figure shows device without belt guard)

3 Description of the device

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

The trainer is mounted on a mobile laboratory frame.

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The intake vessel and pressure vessel are located in the bottom section. The sucked-in air is calmed and the air volume flow measured by the differential pressure sensor and the Venturi nozzle. There are drain plugs for the condensate on the underside of both vessels. The pressure ratios in both vessels are transmitted to the switch cabinet and the software via pressure sensors. In addition, the pressure can be read off manometers on the vessels. The compressor and switch cabinet are located in the top part of the frame. Temperature sensors are located at the connections of the compressor for intake and delivery lines. The speed of the compressor is measured via a photoelectric reflex switch. The compressor is driven via V-belt and pulley. At the same time the cylinder is cooled via blades in the pulley. The delivery line is equipped with a safety valve (set to 10bar). The solenoid valve is opened manually via the switch and compressed air is released via a sound absorber. The pressure switch opens the solenoid valve at approx. 9,5bar. If the pressure switch fails, the safety valve opens at 10bar. When the compressed air is discharged (pressure drop), the signal lamp lights up. The positive pressure prevailing in the vessel is discharged in a defined manner via the blow-off valve.

3 Description of the device

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ET 513

3.2

SINGLE-STAGE PISTON COMPRESSOR

Process schematic

Media

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Air

Main components B1 Intake vessel B2 Pressure vessel M1 Motor Valves and fittings V1 Compressor V01 Solenoid valve V02-V03 Hand valve V04 Non-return valve V05-V06 Condensate drain plug V07 Safety valve X1-X2 Sound absorber Fig. 3.3

Measurement and control equipment P01 Suction pressure P02 Delivery pressure PD03 Differential pressure for volumetric flow rate PSH Pressure switch M01 Motor torque n01 Motor speed n02 Compressor speed T01 Intake temperature T02 Delivery temperature

ET 513: process schematic

3 Description of the device

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

3.3

Components

3.3.1

Pressure switch

Fig. 3.4

Pressure switch

The coordinates of a cut-out pressure of 2bar and a cut-in pressure of 1bar intersect at a point outside the shaded area of the diagram. This value pair can therefore not be set on this pressure switch. Cut-out pressure in bar

Fig. 3.5

The upper pressure value at which the pressure switch interrupts the circuit is called the cut-out pressure. The lower pressure value at which the pressure switch closes the circuit is called the cutin pressure. The cut-off pressure and cut-in pressure can be adjusted on the pressure switch within the range described in the pressure diagram (Fig. 3.5). The coordinates of a cut-out pressure of 8bar and a cut-in pressure of 6bar intersect at a point within the shaded area. These two values can therefore be set on this pressure switch.

Cut-in pressure in bar

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Pressure switches automatically switch motors of pumps or compressors on and off in such a way that the pressure in the pressure vessel does not exceed an upper value or fall below a lower value.

Pressure diagram

3 Description of the device

The pressure switch is supplied already set. The cut-in pressure and the cut-out pressure must not be changed.

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

The diagram also provides additional information: • the highest and lowest value of the cut-out pressure that can be set on the pressure switch • the highest and lowest value of the cut-in pressure that can be set on the pressure switch • the possible cut-in pressure values for a given value of the cut-out pressure

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• the possible cut-out pressure values for a given value of the cut-in pressure • the smallest and largest pressure difference that can be set on the pressure switch

3.3.2

Pressure sensor For measurement data acquisition, the pressures are measured by pressure sensors. The pressure acts via a pressure line (1) directly on a ceramic membrane (2), which deforms when pressure is applied. 1

1 2 Fig. 3.6

2

The electronics applied to the back of the ceramic membrane are influenced by the deformation of the ceramic when pressure is applied. The change is a measure of the pressure.

Pressure line Ceramic membrane Pressure sensor (Fig. similar)

3 Description of the device

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ET 513

3.3.3

SINGLE-STAGE PISTON COMPRESSOR

Manometer Bourdon tube

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Dial plate

Needle

Fig. 3.7

Dial-gauge manometer (Fig. similar)

Fig. 3.8

Type Bourdon tube pressure gauge

The dial-gauge manometers used are of the Bourdon tube pressure gauge style. Bourdon tubes are circular curved tubes with an oval cross-section. The pressure being measured affects the inside of the tube, whereby the oval cross-section approaches a circular shape, since the pressure strives to change the cross-section of the tube to a circle shape. The curvature of the Bourdon tube causes cyclic stress, which bends the spring. The unrestrained end of the spring moves. A mechanism converts the size of this movement into a rotary motion, which then moves the needle and displays the pressure reading on the scale.

3 Description of the device

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ET 513

3.3.4

SINGLE-STAGE PISTON COMPRESSOR

Safety valve Safety valves are used to protect vessels and pipes from excessive pressure loads in the event of failure of upstream automatic control and monitoring devices.

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The safety valves are only supplied already set, i.e. the response pressure cannot be changed.

Fig. 3.9

Safety valve

3.3.5

Non-return valve Compressor

Non-return valves are installed at the end of the compressed air line upstream of the pressure vessel and prevent the vessel pressure escaping after the compressor has been switched off.

Pressure vessel Fig. 3.10

Non-return valve

3 Description of the device

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ET 513

3.4

SINGLE-STAGE PISTON COMPRESSOR

Installation The trainer must be coupled to the HM 365 Universal brake and drive unit in order to create a functional experiment arrangement. 1.

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Snap lock

To do this, align the two units so that they can be connected to each other using the snap locks (there are 2 snap locks on the front and 2 snap locks on the back of the frame). Small tabs welded to the frames make it easier to join them together.

2. HM 365 Fig. 3.11

ET 513

Functional experiment arrangement

Secure both frames with the lockable casters to prevent them from rolling away. Attach the V-belt and tension it. Tensioning the V-belt is described in the HM 365 manual. The large diameter of the pulley results in a reduction ratio of 2,18 : 1. For example, a drive motor speed of 2000min-1 corresponds to a compressor speed of 917min-1.

3 Description of the device

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ET 513

3.5

SINGLE-STAGE PISTON COMPRESSOR

Commissioning

NOTICE The compressor is already installed on the trainer ready for operation.

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NOTICE Risk of damage to the device. • Before connecting to the electrical power supply: Make sure that the laboratory power supply meets the specifications on the device's rating plate.

1.

Connect the mains plug to the electrical power supply of HM 365.

2.

Connect the data transfer cable from the switch cabinet to the HM 365 Universal brake and drive unit.

3.

Connect a PC to the universal brake and drive unit via USB.

4.

Make sure that the compressor is filled with oil.

5.

Make sure that the V-belt is properly tensioned.

6.

Attach the protective hood.

7.

Connect the universal brake and drive unit to the power supply.

The experiment arrangement is now ready.

3 Description of the device

15

ET 513

3.6

SINGLE-STAGE PISTON COMPRESSOR

Operation

11 4 1 13

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19

Fig. 3.12

During operation, the compressor fills the pressure vessel (1) until the pressure switch (4) responds and the solenoid valve (11) is opened. Since the compressor is not switched off, it continues to run while the solenoid valve is open. If for any reason the pressure switch does not respond, the safety valve (13) is opened at 10bar. For longer experiments, the blow-off valve (19) should be opened so that the pressure build-up is considerably delayed. The blow-off valve is used to adjust the air volume flow.

8.

Set the main switch on the universal brake and drive unit to "ON".

9.

Set the speed controller to 0.

10. Set the torque knob to 10. 11. Turn the main switch on the trainer to "ON". The sensors and displays are activated. 12. Set the switch for the direction of rotation on the universal brake and drive unit to "anticlockwise". 13. Turn motor switch to "I". 14. Slowly set the rated speed of the compressor to 980min-1. Read the speed display on the switch cabinet of ET 513, not the display on HM 365).

3 Description of the device

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

3.7

Measurement data acquisition

3.7.1

Installing the software Required for installation: • A ready-to-use PC with USB port (for minimum requirements see Chapter 6, Page 46). • G.U.N.T. CD-ROM

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All components required to install and operate the program are included on the CD-ROM provided by GUNT.

Installation procedure NOTICE While installing the software, the trainer may not be connected to the USB port on your PC. The trainer may only be connected after the software has been successfully installed.

• Start the PC. • Insert GUNT CD-ROM. • Start the installation software "Start.bat". • Follow the installation procedure on screen. • Installation will run automatically after starting it. The following software components are installed onto the PC: – Software for PC-based acquisition of measurement data. – LabVIEW runtime and driver routines. – G.U.N.T. libraries. • After installation of the software, restart the PC.

3 Description of the device

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ET 513

3.7.2

SINGLE-STAGE PISTON COMPRESSOR

Program operation • Select the program and run it via: Start / Programs / G.U.N.T. / ET 513 • The language may be changed at any time in the "Language" menu. • Various pull-down menus are available for other functions.

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• For detailed instructions on use of the program refer to its Help function. The help function is accessed by the "?" button.

Saved measurement data can be imported into a spreadsheet program (e.g. Microsoft Excel®) for further processing.

3 Description of the device

18

ET 513

3.8

SINGLE-STAGE PISTON COMPRESSOR

Care and maintenance

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Maintenance Interval

Activity

At every fitting and removal of the V-belt, at least once a year

Check the V-belt for damage such as cracks and cuts. Replace the damaged V-belt.

See the manufacturer's instructions for the compressor

Check the oil level at the compressor using the sight glass. Top up with oil if necessary. Monograde oil SAE 30 is recommended.

At regular intervals Before the first experiment of the day

Remove condensate from the intake vessel and pressure vessel. To do this, open the drain plug (a) on the underside of the vessels when cold (see Fig. 3.13).

a Care At regular intervals

Fig. 3.13

Drain plug

3 Description of the device

Clean the device with a soft cloth. Do not use caustic or dissolving cleaning agents.

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ET 513

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SINGLE-STAGE PISTON COMPRESSOR

Fundamentals

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The basic principles set out in the following make no claim to completeness. For further theoretical explanations, refer to the specialist literature.

4 Fundamentals

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ET 513

4.1

SINGLE-STAGE PISTON COMPRESSOR

Use of a compressor Compressors are components of compressed air generation systems. These types of system are used wherever compressed air is used as an energy source. Compressed air is used instead of electrical energy, particularly in work places where there is a risk of explosion due to flammable gases, such as mining or in the chemical industry.

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• Mining: Driving machinery • Chemical industry: Control and regulation technology • Workshops, petrol stations: Tools, paint spraying, tyre air • Assembly companies: Automation, pneumatic controls

7

6

5

4 3

2

8

1

Fig. 4.1

4 Fundamentals

Compressed air generating system

21

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Such a system essentially consists of: – Compressor (3) – Drive motor (5) – Pressure vessel (1) – Safety valve (6) – Pressure switch (electric drive) (7) – Manometer (8) All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

– Lines (4) – Frame (2) Air coolers, pressure reducers, water separators etc. may also be present. The compressor is the central component of a compressed air generation system. In it, the mechanical energy supplied is converted into a pressure increase of the air.

4 Fundamentals

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ET 513

4.2

SINGLE-STAGE PISTON COMPRESSOR

Function of a compressor

10

9

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8

Compressors are driven machines that pump gaseous media – in our case air – from regions of low pressure into regions of higher pressure. The energy supplied by driving machines for this purpose – such as by electric motors or internal combustion engines – increases the pressure according to the intended use, but also heats up the air. Part of the heat is dissipated back into the environment by cooling fins.

7 6 5 4 3 2 1

1 2 3 4 5 6 7 8 9 10 Fig. 4.2

Oil sump Crank case Crankshaft Connecting rod Piston pin Piston Cylinder Cylinder cover Suction valve Pressure valve

Fig. 4.2 shows the basic design of a piston compressor. The volume of air enclosed within the cylinder is compressed by the rising compressor and pumped through a pressure valve into the pressure line. In its downward movement, the piston sucks in new air through the suction valve. A crank mechanism, consisting of crankshaft and connecting rod, generates the piston's necessary upwards and downwards movement from a uniform rotary motion. The lubricating oil required to lubricate the moving parts is collected in the oil sump.

Piston compressors

4 Fundamentals

23

ET 513

SINGLE-STAGE PISTON COMPRESSOR

The processes in the compressor can be most clearly represented in a p-v diagram.

p1

p2

1

v

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The p-v diagram shows the pressure in the cylinder over the volume of the respective cylinder. The separate phases of compression are shown in the figures below. The p-v diagram is drawn rotated 90° to the right and thus corresponds to the piston stroke.

p1

p2 2

v

1

p1

p2 3 2

v

1

p1

p2 3

4

2 v

Fig. 4.3

1

– Compression Starting from point 1, the bottom dead centre (BDC), the piston compresses the air in the cylinder. As the volume decreases, the pressure increases. – Discharge In point 2 the pressure in the cylinder has reached the pressure p2 in the pressure line. The pressure valve opens and the compressed air flows into the pressure line. – Re-expansion In point 3 the piston has reached the top dead centre (TDC) and reverses its direction of movement. The pressure valve closes and the air remaining in the cylinder re-expands. The pressure drops. – Intake In point 4 the pressure has fallen to the ambient pressure p1, so that the suction valve opens and fresh air flows into the cylinder. The process continues until the piston reaches the bottom dead centre (BDC). Here, at point 1, the whole process is repeated.

p-v diagram

4 Fundamentals

24

ET 513

SINGLE-STAGE PISTON COMPRESSOR

4.3

Characteristic variables of the piston compressor

4.3.1

Characteristic curves Curves characterise components and systems.

When it comes to compressors, often we are interested in the relationship between pressure difference p between intake side and delivery · side and volumetric flow rate V . Among other things, this relationship is measured using compressor test benches and presented in the form of compressor characteristics.

Pressure differential p

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Compressor characteristics characterise the operating behaviour of compressors.

· Volumetric flow rate V Fig. 4.4

Compressor characteristic, · representation p = f  V 

For compressor characteristics, the inverse func· tion V = f p  is also common in addition to the · representation p = f  V  . Compressor characteristics are often needed in practice, especially when designing systems. During the design process, the system's pressure differential is estimated for the desired volumetric flow rate. This anticipated operating point (head, dependent on volumetric flow rate) is checked to see if it fits well with the compressor characteristic. Compressor characteristics are based on a constant speed. Specifying this speed is part of the compressor characteristics. Changed speeds result in changed compressor characteristics.

4 Fundamentals

25

ET 513

SINGLE-STAGE PISTON COMPRESSOR

· Volumetric flow rate V

Therefore compressor characteristics are recorded at constant speed. The measured values are changed by throttling in the system. The volumetric flow rate is reduced significantly with increasing pressure differential. Piston compressors are usually fitted with a safety valve to protect against exceeding the permitted positive pressure.

Fig. 4.5

Compressor characteristic, representation V· = f p 

Another possibility is to display the volumetric flow rate depending on the compressor speed · V = f  n  at constant pressure.

· Volumetric flow rate V

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Pressure differential p

Fig. 4.6 shows the nearly linear profile of this compressor characteristic.

Compressor speed n Fig. 4.6

Compressor characteristic

4 Fundamentals

26

ET 513

4.3.2

SINGLE-STAGE PISTON COMPRESSOR

Isothermal efficiency The mechanical power Pmech of the compressor is calculated according to:

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P mech = 2    n 2  M Pmech

Mechanical power of the compressor



Mathematical constant  = 3,14

n2

Compressor speed

M

Compressor torque

(4.1)

The isothermal power Pisoth of the compressor (where p1 = 1bar) is:  p2  · - P isoth = p 1  V  In  ----(4.2)  p1  Pisoth

Isothermal power of the compressor

p1

Intake pressure (absolute pressure)

p2 · V

Delivery pressure (absolute pressure) Volumetric flow rate

If Pmech and Pisoth are known, the isothermal efficiency  isoth of the compressor can be calculated: P P mech

isoth  isoth = ---------------

4 Fundamentals

(4.3)

27

ET 513

4.3.3

SINGLE-STAGE PISTON COMPRESSOR

Volumetric efficiency

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The volumetric efficiency is the ratio of the pumped mass to the theoretical mass. The volumetric efficiency shows the utilisation of the displaced volume Vstroke by the pumped medium, thus representing the volumetric efficiency of the compressor. · V m  L = --------------------------V stroke  n 2 L

(4.4)

Volumetric efficiency

· Vm

Volumetric flow rate

Vstroke

Displaced volume

n2

Compressor speed

Volumetric efficiency VE =  L  100%

4.3.4

(4.5)

Pressure ratio The pressure ratio  indicates the ratio of delivery pressure p2 to intake pressure p1. p  = -----2(4.6) p1

4 Fundamentals



Pressure ratio

p1

Intake pressure (absolute pressure)

p2

Delivery pressure (absolute pressure)

28

ET 513

4.3.5

SINGLE-STAGE PISTON COMPRESSOR

Measuring the volumetric flow rate using a Venturi nozzle (differential pressure sensor) Differential pressure / Volumetric flow rate: The differential pressure in a venturi nozzle is proportional to the square of the volumetric flow rate: ·  dpV = An  2 -------------

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

dp

(4.7)

Where: · V = Volumetric flow rate in m3 /s dp = Differential pressure in N/m2

 = Density in kg/m3

Fig. 4.7

Venturi nozzle / Pressure curve

An = Cross-section area (narrowest flow cross-section)

Density of air: The density  of air is dependent upon the ambient temperature T and the air pressure p0. If we assume that the air behaves similarly to an ideal gas, then we get: 100  p

0  = ----------------------------------R s   T + 273 

(4.8)

Where: p0 = Ambient pressure 1013mbar Rs = Specific gas constant of air 287J   kg  K  T = Ambient temperature in °C.

4 Fundamentals

29

ET 513

5

SINGLE-STAGE PISTON COMPRESSOR

Experiments

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The selection of experiments makes no claims of completeness but is intended to be used as a stimulus for your own experiments. The results shown are intended as a guide only. Depending on the construction of the individual components, experimental skills and environmental conditions, deviations may occur in the experiments. Nevertheless, the laws can be clearly demonstrated.

The experiments measure the relevant pressures p2 and p1, the speed n1 and torque M1 of the drive motor, the speed n2 of the compressor, the · sucked-in air volumetric flow rate V and the relevant temperatures T1 and T2. This allows us to calculate the most important key figures for the compressor.

5 Experiments

30

ET 513

SINGLE-STAGE PISTON COMPRESSOR

5.1

Series of measurements 1: Operating the compressor at constant speed

5.1.1

Objective of the experiment

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In this experiment, the delivery pressure of the compressor is gradually changed while the intake pressure and the speed remain constant. Various characteristics are measured and calculated. How the characteristics depend on the pressure ratio is shown.

5.1.2

Preparation for the experiment 1.

Before the first experiment of the day: Drain the pressure vessel. To do this, open the condensate drain plugs V05 and V06. Close them as soon as no more water escapes.

2.

Commission the compressor in accordance with Chapter 3.5, Page 15.

3.

Open valves V02 and V03.

4.

Set the main switch on the universal brake and drive unit to "ON".

5.

Set the speed controller to 0.

6.

Set the torque knob to 10.

7.

Turn the main switch on the trainer to "ON". The sensors and displays are activated.

5 Experiments

8.

Set the switch for the direction of rotation on the universal brake and drive unit to "anticlockwise".

9.

Turn motor switch to "I".

31

ET 513

SINGLE-STAGE PISTON COMPRESSOR

10. Slowly set the rated speed of the compressor to 820min-1. Read the speed display on the switch cabinet of ET 513, not the display on HM 365).

5.1.3

Conducting the experiment

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11. Measure and note down: Air pressure and ambient temperature. 12. Wait until a steady state has been reached. 13. Take the following measurements: Motor speed n1, motor torque M1, intake pressure p1, delivery pressure p2, volumet· ric flow rate V , intake temperature T1 and delivery temperature T2. 14. Reduce the air volumetric flow rate using the blow-off valve V03 so that the delivery pressure increases by approx. 1bar. 15. Repeat steps 12 to 14 until the delivery pressure reaches approx. 9bar. 16. Open the blow-off valve V03. 17. Set the speed controller to 0. 18. Turn motor switch to "0". 19. Turn the main switches of the trainer ET 513 and the universal brake and drive unit to "OFF".

5 Experiments

32

ET 513

5.1.4

Measured values Speed Motor

Torque Motor

Suction pressure

Delivery pressure

n1 in min-1

M1 in Nm

p1 in bar abs

p2 in bar g

1

1785

1,64

1,0

0,1

2

1789

2,31

1,0

3

1786

2,60

4

1785

5

Measurement series

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SINGLE-STAGE PISTON COMPRESSOR

Volumetric Intake temflow rate perature · V in L/min

Delivery temperature

T1 in °C

T2 in °C

117

22,1

66,4

1,2

111

22,4

94,1

1,0

2,0

106,2

23,4

111,6

2,90

1,0

3,1

101

24,6

131,0

1786

3,13

1,0

4,1

97

25,4

148,0

6

1781

3,32

1,0

5,1

93

27,0

164,5

7

1785

3,45

1,0

6,0

89

27,9

174,0

8

1788

3,59

1,0

7,0

86

28,6

179,0

9

1782

3,69

1,0

8,2

83

29,3

181,0

10

1788

3,86

1,0

9,3

81

29,7

189,2

Tab. 5.1

Example measured values

5 Experiments

33

ET 513

5.1.5

Measurement series

SINGLE-STAGE PISTON COMPRESSOR

Analysis of the experiment Power Motor

Power Compressor

 isoth Pmech in W Pisoth in W

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Isothermal efficiency

in %

Volumetric efficiency

Volumetric efficiency

Pressure ratio

Pressure difference

L

VE in %



p

1

303

38

11

0,93

93

1,1

0,1

2

432

150

35

0,89

89

2,2

1,2

3

486

195

41

0,84

84

3,0

2,0

4

545

233

43

0,80

80

4,1

3,1

5

584

257

44

0,77

77

5,1

4,1

6

619

275

44

0,73

73

6,1

5,1

7

644

282

44

0,71

71

7,0

6,0

8

672

290

43,75

0,69

69

8,0

7,0

9

693

302

43,25

0,66

66

9,2

8,2

10

716

308

43

0,65

65

10,3

9,3

Tab. 5.2

Calculated values

5 Experiments

34

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Isothermal efficiency  isoth in %

100 90 80 70 60 50 40 30 20 10 0 0

2

4

6

8

10

12

10

12

Pressure ratio  Fig. 5.1

Volumetric efficiency  L

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Isothermal efficiency  isoth and volumetric efficiency  L over the pressure ratio  = p2 /p1 are represented as a curve in a chart.

Isothermal efficiency over pressure ratio at constant speed 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 0

2

4

6

8

Pressure ratio  Fig. 5.2

5 Experiments

Volumetric efficiency over pressure ratio at constant speed

35

ET 513

5.1.6

SINGLE-STAGE PISTON COMPRESSOR

Evaluation The characteristics provide the following results: – the pressure difference decreases increasing volumetric flow rate.

with

– the isothermal efficiency increases with increasing pressure ratio and remains almost constant from a pressure ratio of approx. 4.

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– the volumetric efficiency increasing pressure ratio.

5 Experiments

decreases

with

36

ET 513

SINGLE-STAGE PISTON COMPRESSOR

5.2

Series of measurements 2: Operating the compressor at constant pressure

5.2.1

Objective of the experiment

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In this experiment, the speed of the compressor is changed gradually, while the delivery pressure p2 remains constant, by adjusting it with the blow-off valve V03. Various characteristics are measured and calculated. How the characteristics depend on the pressure ratio is shown.

5.2.2

Preparation for the experiment 1.

Drain the pressure vessel before the first experiment of the day. To do this, open the condensate drain plugs V05 and V06. Close them as soon as no more water escapes.

2.

Commission the compressor in accordance with Chapter 3.5, Page 15.

3.

Open valves V02 and V03.

4.

Set the main switch on the universal brake and drive unit to "ON".

5.

Set the speed controller to 0.

6.

Set the knob for torque to 10.

7.

Turn the main switch on the trainer to "ON". The sensors and displays are activated.

5 Experiments

8.

Set the switch for the direction of rotation on the universal brake and drive unit to "anticlockwise".

9.

Turn motor switch to "I".

37

ET 513

SINGLE-STAGE PISTON COMPRESSOR

10. Slowly set the rated speed of the compressor to 980min-1. Read the speed display on the switch cabinet of ET 513, not the display on HM 365).

5.2.3

Conducting the experiment

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11. Measure and note down: Air pressure and ambient temperature. 12. Wait until a steady state has been reached. 13. Take the following measurements: Motor speed n1, compressor speed n2, motor torque M1, intake pressure p1, deliv· ery pressure p2, volumetric flow rate V . 14. Reduce the speed by 90...100min-1. 15. Set the blow-off valve V03 so that the delivery pressure corresponds to the delivery pressure of the first measured value recording, such that this remains constant. 16. Repeat steps 12 to 15 until the delivery pressure of the first measured value recording is no longer reached. 17. Open the blow-off valve V03. 18. Set the speed controller to 0. 19. Turn motor switch to "0". 20. Turn the main switches of the trainer ET 513 and the universal brake and drive unit to "OFF".

5 Experiments

38

ET 513

5.2.4

SINGLE-STAGE PISTON COMPRESSOR

Measured values Speed Motor

Torque Motor

Suction pressure

Delivery pressure

Speed Compressor

n1 in min-1

M1 in Nm

p1 in bar abs

p2 in bar g

n2 in min-1

· V in L/min

1

2132

3,87

1,0

9,0

980

93

2

1929

3,88

1,0

9,0

883

85

3

1724

3,80

1,0

9,0

789

78

4

1530

3,69

1,0

9,0

704

70

5

1330

3,69

1,0

9,0

608

59

6

1130

3,48

1,0

9,0

518

49

7

930

3,56

1,0

9,0

426

41

8

730

3,56

1,0

9,0

338

33

9

600

3,80

1,0

9,0

275

24

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Measurement series

Tab. 5.3

5 Experiments

Volumetric flow rate

Example measured values

39

ET 513

Analysis of the experiment

Measurement series

Power Motor

Power Compressor

Isothermal efficiency

Volumetric efficiency

Volumetric efficiency

Pmech in W

Pisoth in W

 isoth in %

L

VE in %

1

860

348

40

0,62

62

2

780

321

41

0,63

63

3

689

297

43

0,64

64

4

592

264

45

0,65

65

5

480

230

45

0,64

64

6

415

191

46

0,63

63

7

347

156

45

0,63

63

8

274

125

45

0,62

62

9

230

96

38

0,60

60

Tab. 5.4

Calculated values

· Volumetric flow rate V

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5.2.5

SINGLE-STAGE PISTON COMPRESSOR

100 90 80 70 60 50 40 30 20 10 0 200

Fig. 5.3

300

400

500 600 700 800 Compressor speed n2 in min-1

900

1000

Compressor characteristic

Isothermal efficiency  and volumetric efficiency  L are represented in a chart as a curve over the compressor speed n2.

5 Experiments

40

SINGLE-STAGE PISTON COMPRESSOR

100 90 80 70 60 50 40 30 20 10 0 200

300

400

500

600

700

800

900

1000

Speed n2 in min-1 Fig. 5.4

Volumetric efficiency  L

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Isothermal efficiency  isoth in %

ET 513

Isothermal efficiency over compressor speed at constant pressure 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 200

300

400

500

600

700

800

900

1000

Speed n2 in min-1 Fig. 5.5

5 Experiments

Volumetric efficiency over compressor speed at constant pressure

41

ET 513

5.2.6

SINGLE-STAGE PISTON COMPRESSOR

Evaluation The characteristics provide the following results: – The volumetric flow rate increases proportionately with the speed. – The isothermal efficiency decreases slightly with increasing speed or is almost constant.

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– The volumetric efficiency remains almost constant even with increasing speed.

5 Experiments

42

ET 513

5.3

SINGLE-STAGE PISTON COMPRESSOR

Consideration of both measurement series Isothermal efficiency As far as efficiency is concerned, it can be said that  isoth is above all a function of the pressure ratio  . This is confirmed not only by the results, but also by the equation for calculating the efficiency.

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Volumetric efficiency The ratios for the volumetric efficiency are not quite so clear: The volumetric efficiency is made up of three different terms:

L = D  F  A

(5.1)

 D is referred to as the throughput rate and shows the influence of leaks in piston rings, valves and packing glands. It is set to 1 for well maintained and new machines.

 F is referred to as the filling ratio and is the quotient of the indicated suction volume V and the displacement per cylinder Vstroke. The filling ratio measures the flow and throttle losses as well as the volume decrease due to the re-expansion.

 A is referred to as the heating ratio and is used to assess volume losses due to heating of the pumped medium during suction. The temperature rise of the gases during suction T1 is caused by their heating at the walls of the working area. As the mean cylinder temperature increases with increasing pressure ratio  , and thus also the temperature at compression T2, the heating ratio

5 Experiments

43

ET 513

SINGLE-STAGE PISTON COMPRESSOR

becomes smaller. These relationships can be represented approximately as equations: T1 -----T2

(5.2)

Heating ratio  A

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Fig. 5.5 shows the heating ratio as a function of the pressure ratio  . 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 0

2

4

6

8

10

12

Pressure ratio  Fig. 5.6

5 Experiments

Heating ratio as a function of pressure ratio

44

ET 513

SINGLE-STAGE PISTON COMPRESSOR

For the two measurement series, the volumetric efficiency curves are evaluated as follows: – Series of measurements 1 As the pressure ratio increases, the volumetric efficiency is mainly influenced by the heating ratio and decreases accordingly. – Series of measurements 2

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The volumetric efficiency decreases with increasing volumetric flow rate (corresponds to increasing speed), as the throttle losses increase with increasing volumetric flow rate. The re-expansion  0 can be neglected in the compressor being studied because of the small dead space and the relatively low pressure ratios.

5 Experiments

45

ET 513

SINGLE-STAGE PISTON COMPRESSOR

6

Appendix

6.1

Technical data Dimensions Length x Width x Height Weight

900 x 800 x 1,510 mm approx. 130 kg

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Voltage supply Voltage Frequency Phases Nominal consumption (power) Alternatives optional, see rating plate Noise emissions

up to 90 dB(A)

Compressor Power consumption Rated speed Positive operating pressure Max. pressure Intake capacity at 8bar g Inner diameter Stroke Oil quality Oil quantity Oil top-up quantity

230 V 50 Hz 1 0,4 kW

1 cylinder, single-stage 0,75 980 8 10 105 65 46 SAE 30 0,25 0,13

kW min-1 bar bar L/min mm mm L L

NOTICE The compressor is not operated with refrigerant but rather with air. Only use oil appropriate for air.

6 Appendix

46

ET 513

SINGLE-STAGE PISTON COMPRESSOR

V-belt Type Length

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Speed sensor Type Measuring range

SPA 1,500 mm

Photoelectric reflex switch 0...1.000 min-1

Safety valve Blow-off pressure

10 bar

Pressure vessel Volume Maximum pressure

20 L 16 bar

Intake vessel Volume

20 L

Pressure measurement Delivery pressure Intake pressure Pressure sensor Measuring range Temperature measurement Temperature sensor Measuring range Venturi nozzle differential pressure sensor Narrowest flow cross-section An

6 Appendix

0...16 bar -1...1,5 bar

0...16 bar abs.

type Pt100 -50...300 °C

113 mm2

47

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ET 513

SINGLE-STAGE PISTON COMPRESSOR

Measurement data acquisition Software environment: LabVIEW Runtime System requirements: PC with Pentium IV processor, 1GHz Minimum 1024MB RAM Minimum 1GB free hard disk space 1 CD-ROM drive 1 USB port Graphic card resolution min. 1024 x 768 pixels, True Color Windows 7 / Windows 8 / Windows 10

6.2

6 Appendix

List of formula symbols and units Formula symbols

Mathematical/physical variable

Unit

An

Venturi nozzle cross-section area

mm2

i

Transmission ratio

–

M1

Motor torque

Nm

n2

Compressor speed

n1

Motor speed

p1

Suction pressure

p2

Delivery pressure

Pisoth

Isothermal power

Pmech

Mechanical power

Rs

Specific gas constant

T1

Intake temperature

T2

Delivery temperature

VE

Volumetric efficiency

%

Vstroke · V · V meas

Displaced volume

dm3

Measured volumetric flow rate

0

Re-expansion

min-1

bar

W, kW J/  kg  k  °C

Volumetric flow rate

m3/h –

48

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ET 513

6.3

SINGLE-STAGE PISTON COMPRESSOR

Formula symbols

Mathematical/physical variable

Unit

p

Differential pressure

bar

A

Heating ratio

–

D

Throughput rate

–

F

Filling ratio

–

L

Volumetric efficiency

–



Pressure ratio

–



Density

kg/m3

Tables and graphs Unit

L/s

L/min

L/h

m3/min

m3/h

1L/s

1

60

3600

0,06

3,6

1L/min

0,01667

1

60

0,001

0,06

1L/h

0,000278

0,01667

1

0,00001667

0,001

1m /min

16,667

1000

60000

1

60

1m3/h

0,278

16,667

1000

0,01667

1

3

Tab. 6.1

Conversion table for units of volume flow

Unit

mbar

Pa

hPa

kPa

mm WC *

1bar

1

1,000

100,000

1,000

100

10,000

1mbar

0,001

1

100

1

0,1

10

1Pa

0,00001

0,01

1

0,01

0,001

0,1

1hPa

0,001

1

100

1

0,1

10

1kPa

0,01

10

1,000

10

1

100

1 mm WC *

0,0001

0,1

10

0,1

0,01

1

Tab. 6.2

6 Appendix

bar

Conversion table for units of pressure * rounded values

49

ET 513

SINGLE-STAGE PISTON COMPRESSOR

6.4

Worksheets

6.4.1

Worksheet 1: Measured values

Ambient temperature:

_______

Ambient pressure:

_______

Motor (HM 365) Measurement n1 in min-1 series

M1 in Nm

Compressor (ET 513) p1 in bar

p2 in bar

T1 in °C

T2 in °C

·

n2 in min-1 V in L/min

1 All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

6 Appendix

50

ET 513

SINGLE-STAGE PISTON COMPRESSOR

6.4.2

Worksheet 2: Calculations

Ambient temperature:

_______

Ambient pressure:

_______

Measurement series

Pmech in kW

Pisoth in kW

 isoth in %

L

VE in %



p in bar

1 2

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

6 Appendix

51

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Isothermal efficiency  isoth in %

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

6.4.3

Worksheet 3: Isothermal efficiency over pressure ratio 100 90 80 70 60 50 40 30 20 10 0 0

2

4

6

8

10

12

Pressure ratio 

6 Appendix

52

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Volumetric efficiency  L

6.4.4

Worksheet 4: Volumetric efficiency over pressure ratio 1,0 0,9 0,8 0,7 0,6

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

0,5 0,4 0,3 0,2 0,1 0 0

2

4

6

8

10

12

Pressure ratio 

6 Appendix

53

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Isothermal efficiency  isoth in %

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

6.4.5

Worksheet 5: Efficiency over compressor speed 100 90 80 70 60 50 40 30 20 10 0 200

300

400

500

600

700

800

900

1000

Compressor speed n2 in min-1

6 Appendix

54

ET 513

SINGLE-STAGE PISTON COMPRESSOR

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

Volumetric efficiency  L

6.4.6

Worksheet 6: Volumetric efficiency over compressor speed 0,7 0,6 0,5 0,4 0,3 0,2 0,1 0 200

300

400

500

600

700

800

900

1000

Compressor speed n2 in min-1

6 Appendix

55

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Heating ratio  A

6.4.7

Worksheet 7: Heating ratio over pressure ratio 0,35 0,3 0,25 0,2

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

0,15 0,1 0,05 0 0

2

4

6

8

10

12

Pressure ratio 

6 Appendix

56

ET 513

SINGLE-STAGE PISTON COMPRESSOR

· Volumetric flow rate V in L/min

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

6.4.8

Worksheet 8: Compressor characteristic volumetric flow rate over compressor speed 100 90 80 70 60 50 40 30 20 10 0 200

300

400

500

600

700

800

900

1000

Compressor speed n2 in min-1

6 Appendix

57

ET 513

SINGLE-STAGE PISTON COMPRESSOR

Pressure difference p in bar

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

6.4.9

Worksheet 9: Compressor characteristic pressure difference over volumetric flow rate 10

5

0 0

25

50

75

100

125

150

· Volumetric flow rate V in L/min

6 Appendix

58

ET 513

SINGLE-STAGE PISTON COMPRESSOR

· Volumetric flow rate V in L/min

All rights reserved, G.U.N.T. Gerätebau, Barsbüttel, Germany 10/2018

6.4.10

Worksheet 10: Compressor characteristic volumetric flow rate over pressure difference 150

125

100

75

50

25

0 0

5

10

Pressure difference p in bar

6 Appendix

59