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P.A. HILTON LTD

EXPERIMENTAL

OPERATING

AND

MAINTENANCE MANUAL

TWO STAGE COMPRESSOR TEST UNIT

F865

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(i)

POLICY STATEMENTAfter Sales Service

We, P.A. Hilton Ltd., attach considerable importance in being able to retain the confidence and goodwill

of our clients in offering an effective after sales service. Every effort is made to answer clients

correspondence promptly and to provide a rapid follow up of spares and replacement parts by maintaining

comprehensive stocks of components usually available ex-stock.

Should our clients encounter any difficulty in operating or maintaining a Hilton product we would ask that

as a first step they contact the Hilton representative in their country or, in the absence of a local

representative, write direct to P.A. Hilton Ltd.

In the extreme case a problem may arise in the operation of equipment which could seriously disrupt a

teaching or research schedule. In such circumstances rapid advice from the manufacturers is desirable and

we wish our clients to know that Hiltons' will accept from them a transfer charge telephone call from

anywhere in the world.

We ask our clients to treat this service as an emergency service only and to use it sparingly and wisely.

Please do be aware of the time differences that may exist and, before making a telephone call, make notes

of the problem you wish to describe. English is a preferred language. Our telephone number is "Romsey(01794) 388382" and the telephone is normally manned between 0800 and 1700 hrs GMT every day.

Advance notice of an impending telephone call by fax would be appreciated.

Each product manufactured by P.A. Hilton Ltd., is tested under operating conditions in our permanent

installations before despatch. Visitors to Horsebridge Mill are encouraged to operate and evaluate our

equipment with initial guidance from a Hilton engineer

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(ii)

EDUCATION AND TRAINING EQUIPMENT

Declaration of Conformity:Directives(where appl icable) 89/392/CEE as amended by 91/368/EEC

89/336/CEE72/23/CEE

We declare that the following unit complies with the above EEC directives:

F865 Two Stage Compressor Test Unit

The use of the apparatus outside the classroom, laboratory, study area or similar such place invalidates

conformity with the protection requirements of the Electromagnetic Compatibility Directive (89/336/EEC)

and could lead to local prosecution.

For and on behalf of

P.A. HILTON LIMITED

Technical Director

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(iii)INDEX

SCHEMATIC DIAGRAMS 1INTRODUCTION 6

SCHEMATIC DIAGRAM NOTATION 6INSTALLATION 6

Water and Drain Connection 12

Test Running After Installation. 12

DESCRIPTION 14The compressor module. 14

The Control Console 16

PRECAUTIONS AND WARNINGS 17

OPERATING PROCEDURES 18

Starting and Maintaining Stable Conditions as a Two Stage Compressor 18

Adjustment or Removal of Intercooling Effect 18

MAXIMUM OPERATING PRESSURE 19

Starting and Maintaining Stable Conditions as a Single Stage Compressor 19

Stopping and Shutting Down 20

MAINTENANCE 21

Compressor Module 21

Control Console 21

USEFUL DATA 22

Compressor Dimensions 22

Air Flow Measurement 22

1. INVESTIGATION OF VARIATION IN AIR FLOW RATE, WITH COMPRESSORPRESSURE RATIO:- With and Without Intercooling 24

2. INVESTIGATION OF VARIATION IN VOLUMETRIC EFFICIENCY WITHCOMPRESSOR PRESSURE RATIO:- With and Without Intercooling 313. INVESTIGATION OF VARIATION OF ISOTHERMAL EFFICIENCY WITH

COMPRESSOR PRESSURE RATIO:- With and Without Intercooling 35

4. INVESTIGATION OF THE COMPRESSOR PERFORMANCE RELATIVE TOELECTRICAL POWER, SHAFT POWER, AND HEAT LOSS:- With and Without

Intercooling 43

BLANK OBSERVATION TABLE 52

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1

Control Console Front Panel

MainSwitch

Tachometerlead

MotorTachometer

OrificePlateMan

ometer

CompressorAmm

eter

CompressorVoltmeter

TemperatureIndi

cator

8.

TemperatureSelectorSwitch

9.

ThermocoupleSockets

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Control Console Rear Panel

10.

MainPowerInlet

11.

PortforOptionalDataLo

ggerUpgrade

12.

2.5AMAXpoweroutletforoptionalDataLogger

13.

PoweroutletforCompressor

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Compressor Module (Detail)

20. 2nd

Stage Pressure Gauge21. 2ndStage Safety Valve (11Bar)22. Intake Orifice / Damping vessel32. Receiver Discharge / Vent Valve.33. Compressor ON SWITCH (Green)

34. Compressor OFF / STOP SWITCH (RED)35. Pressure Switch

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UNITS Symbol DesignationUnit

f Dynamometer balance load kg

g Acceleration due to gravity m/s2

h Orifice plate pressure differential mmWg

I Electric motor current Amps

Airm&

Air mass flow rate kg/s

N Rotational speed 1/second

p Gauge pressure kN/m2

P Absolute pressure kN/m2

vq Air volume flow rate Litres/second

Q& Heat transfer Watts

r Motor dynamometer torque arm radius m

R Gas constant for air kJ/kgK

t Temperature C

T Absolute temperature K

v Volume m3

Vs Swept volume Litres/second

V Motor supply voltage Volts

W Work or high grade energy(electrical) Watts

Ratio of specific heats -

Efficiency %

Rotational speed radians/second

Suffix Description

Ambient Ambient condition

c Compressor

Em Electric Motor

i Inlet Condition

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INTRODUCTION

The reciprocating air compressor is a fundamental subject for thermodynamic analysis and study. The

process of induction and compression is a cyclic one. However by the use of a large reservoir on intake

and discharge the system can be examined as a steady flow process.

The Hilton Single Stage Compressor Test Unit F860allows the compression process to be analysed in

detail. However for larger volume compressors the compression process is divided into multiple stages

with cooling of the compressed air after each stage being used to reduce the energy required to drive the

compressor.The Hilton Two Stage Compressor Test Unit F865 allows students to investigate two stage

compression, both with and without the use of an intercooler and to operate the unit as a single stage

compressor.

A small bench mounted control console provides instrumentation and control for the compressor module

which is a belt driven unit with intake, intermediate and discharge reservoirs to smooth out the pressure

pulsations. An orifice plate flow measuring device is included in the air inlet and this connects to a

manometer mounted on the control console.

Pressure gauges on the reservoirs allow the first and second stage pressures to be measured. An ammeter

and voltmeter connected to the motor power supply allow the motor load to be monitored as the

compressor pressure ratio is increased. A tachometer sensor on the motor drive connects to the control

console mounted display..

A water cooled intercooler reduces the air temperature between stages and a water flowmeter allowsflow measurement and control.

Thermocouples on the compressor inlet and outlet at each stage and on the intercooler water flowsallow all relevant temperatures to be measured.

All of the instruments supplied allow the unit performance to be examined in detail.

An optional Computerised Data Acquisition system FC865A is available complete with its ownInstallation, Operating and Maintenance Manual. The unit has been designed so that the upgrade

components can be fitted at any time during the life of the unit. In addition, the unit and upgrade havebeen designed to allow installation by any competent technician.

SCHEMATIC DIAGRAM NOTATIONTo assist in identifying all of the components there are three annotated schematic diagrams on pages 1,2 and 3 . Each relevant component has a number identifier. In order to simplify componentidentification in the text the relevant number is placed alongside the component name which is also inbold text. For example on page 1 the main switch would be identified in text as main switch(1).Thi ti i d th h t th l

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tighten. Note that the end of the pipe can be directed under the 2

nd

stage receiver(27). It isMOST IMPORTANT that the air discharge pipe or a suitable alternative is connected to

the receiver discharge/vent (32). The vent valve MUST NOT be allowed to vent openly

with nothing connected to it. Refer to the safety precautions on page 17.

3. If the unit is supplied with the optional computerised data acquisition upgrade FC865A

factory fitted there will be additional leads and cables to connect to the data logger module

that is part of the upgrade. This is dealt with in the computerised data acquisition manual

that is supplied as part of this manual.

4. Assuming the unit is not supplied with the optional computerised data acquisition system

FC865A then proceed as follows.Locate the air intake vessel adjacent to the unit.

The pressure tapping shown at A is connected using the small diameter hose supplied to the

suction tapping on the orifice plate manometer(4).This measures the pressure drop across theorifice plate shown at C. The large diameter hose is used to connect the 1

st stage air intake

pipe(28)on the compressor to the suction coupling B on the air intake vessel as shown above.

Tighten both hose clamps to ensure an air tight seal.

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The manometer will normally require filling using the red fluid supplied. Fill to the zero (0mm)

mark on the adjustable scale. Connect the hose to the low pressure coupling on the orifice plate

manometer(4)as shown below.

5. Connect the motor tachometer sensor lead to the socket below the motor tachometer(3)display

on the control console as shown below.

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10. The local power supply must also be connected to the control console through cable gland main

power inlet (10)in the rear panel.

The local power supply must be capable of supplying the current ( Amps per phase) that is

indicated on the compressor motor plate. Note that in accordance with local regulations thepower supply must also have suitably rated fuses or overload cut out devices and it must also

have a low resistance Earth or Grounding point. It is recommended that the supply also has anisolator switch.The cables from the local supply to the unit must comply with local regulations and be suitablyprotected (conduit or a bundled conductor) .

The compressor operates on a 3 phase balanced supply and depending upon the local supplyvoltage, the instrumentation console operates on a single phase supply with neutral (or otherarrangement as specified below).

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Note that the device shown as E is the RCCB or earth leakage circuit breaker. This constantlymonitors the incoming and outgoing current in the circuit and in the event of a leakage toground above 30mA it will disconnect the power. The test button is shown adjacent to Eabove and the reset button is below. Note that ON is UP .

The switch on the right above shown as D is the main overload cut out. This will disconnect

the power in the event of an overload or short circuit. To reset the cut out the switches underD are lifter UP.When all cables are correctly secured re-assemble and close the instrument console.

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Water and Drain Connection11. The unit requires a water supply for the intercooler and a drain to receive the heated water.

The water is connected at the rear of the cooling water flowmeter(16)on the compressormodule.

Note that if the optional data logging system has been purchased and factory fitted the waterinlet hose will already be connected at this point. The reinforced inlet hose supplied has a pushfit nozzle to match the coupling at the bottom of the flowmeter.

A similar hose connects to the outlet coupling adjacent to the T6 themocouple point as shown

below.

WARNINGThe hose should be firmly securedin a drain that is capable of receiving the water. Note that

the drain must be secured as it is used to vent water from the heat exchanger when not in use.The compressed air supply is used to flush the water from the heat exchanger.

Test Running After Installation.

Ensure that the motor belt cover is fully secure.Ensure that the compressor has oil in its sump by viewing through the window in the side of

the compressor.

f i h l l l h h S ( )

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DO NOT move the EARTH/ground conductor or NUETRAL conductor. These MUST stay intheir correct location.

Ensure valve A (24)is open (Turned Anti-clockwise), valve B (25)is closed and the waterpurge valve(26)is closed. Also close the receiver discharge/vent valve(32).

Check that the water drain valve shown below the receiver(27)is closed.

Finally press the green compressor ON switch(33)on the pressure switch(35)body and thecompressor will start.

Air may be heard venting from the high pressure switch(35) area. This is normal. The highpressure switch(35)also activates a compressor unloading device to aid starting when the main

air receiver(27)is at high pressure.

Ensure that the motor tachometer(3) indicates the motor speed and that the orifice platemanometer(4)shows a positive differential pressure. If the pressure is negative reverse theplastic pipe location on the manometer.

Open the valve on the cooling water flowmeter(16) and ensure the water flows through the

meter and leaves via the drain hose.Monitor the 1ststage pressure(17)gauge and the 2ndstage pressure gauge(20).Ensure both

are increasing.

To turn off the compressor press the red compressor Off/stop switch(34). NOTE that themain switch(1) on the instrument console ONLY turns off power to the instruments. It

does NOT turn off the compressor..

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DESCRIPTION

Please refer to the Schematic Diagrams on page 1, 2, 3and 4.

The standard unit includes a compressor module and a control console. An optional computerised dataacquisition option is also available and this is dealt with in a separate section of the manual.

The compressor module.

The compressor(14)is mounted together with its drive motor(15)on top of the 2ndstage airreceiver(27) .

Air is drawn into the unit through the intake orifice/damping vessel(22) attached to the 1ststage

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can be closed and valve B(25)opened to operate the unit as a single stage compressor.

The motor speed is monitored by a sensor which connects directly to the motor tachometer(3)displaywhich is mounted on the front panel of the separate control console.

As the compressed air is likely to contain moisture which will condense in the 2ndstage air

receiver(27)a drain valve is located under one end of the receiver.

The relevant temperatures of air and water are recorded by 6 insulated thermocouples located asrequired on the unit. All six thermocouples are duplex ready for the optional FC865A computeriseddata acquisition option that can be added at any time.All thermocouples plug into sockets on the separate control console.

The 1ststage receiver(18)is fitted with a safety valve(19)set to operate at 4 Bar gauge. This isprimarily to prevent overloading of the motor due to the large diameter of the low pressure cylinder.

The compressor is fitted with a high pressure switch(35). This is factory set to operate at 10Bar gauge

and is connected to the 2ndstage air receiver(27). The 2ndstage outlet air receiver(27)has a safeworking pressure of 11 Bar gauge and a safety valve(21) is also fitted to the receiver set to vent at 11bar gauge.

The inlet to the 2ndstage air receiver(27)is fitted with a non-return valve and an unloading valve.The combined high pressure switch(35)also has an unloading device that allows the compressor tostart under zero pressure conditions even when the 2ndstage air receiver(27) is at high pressure. This

prevents overloading of the compressor motor and ensures a long operating life.

The compressor Green on switch(33) and Red stop switch(34)are both located on top of the high

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The Control Console.

The control console is used as the main electrical supply to the compressor module and to carry all ofthe instrumentation except for the pressure gauges.

The power from the local supply enters the rear panel main power inlet(10). An internal RCCB orearth leakage circuit breaker constantly monitors incoming and outgoing current and in the event of animbalance of 30mA or more (as in a leakage to earth situation) the RCCB will disconnect the power.

This is for operator protection in the event of a local earthing failure combining with an internal fault.

The console also contains the main overload cut out device which will disconnect the unit from thesupply in the event of an overload or short circuit. Both RCCB and overload are internally mounted

and the case will need to be opened to reset the devices.

The main switch(1)is a double pole switch and overload cut out. This supplies power to theinstrumentation only. NOTE that the main switch(1) does not turn off the compressor.The mainswitch will disconnect the instrumentation from the supply in the event of a fault with the small currentloads of the instruments.

The motor tachometer(3)displays the motor speed in revolutions per minute(rpm) . The ammeter(5)

and voltmeter(6)indicate the electrical power supplied via the rear power outlet(13)to thecompressor..

The digital temperature indicator(7) will indicate the temperature of the thermocouples connected to

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PRECAUTIONS AND WARNINGS

IMPORTANT

If used carelessly compressed air can be highly dangerous and potentially lethal. Debris

projected by compressed air can be as deadly as a conventional rifle bullet.

Compressed air alone if directed at the human body can be deadly resulting in loss of eyes,

embolism(bubbles in the bloodstream), loss of hearing and death in several recorded cases.

It is important that locally applicable safety precautions are fully explained to students beforeoperating the F865 Two Stage Compressor Test Unit.

The following are a list of general safety comments. There will be others that are covered by localregulations.

1. A discharge pipe is supplied to be fitted to the receiver discharge/vent valve(32).This isdesigned to direct the high pressure air under the 2ndstage air receiver(27)at floor level.

2. The unit MUST NOT be operated with nothing connected to the outlet receiverdischarge/vent valve(32).Venting compressed air at this level can be highly dangerous.

3. It is not recommended by P.A.Hilton Ltd but it is possible of course for the user to connectother suitably pressure rated air tools to the outlet control valve(32) . However the operation

and safety aspects of such devices are entirely the responsibility of the user.4. It is recommended that safety goggles are used by persons operating the compressor,

particularly if the local area is dusty or there is loose debris on the floor that may get blowninto eyes.

5. The compressor can generate pressures up to 10 Bar gauge. The high pressure switch isdesigned to turn off the compressor at 10 bar gauge. Do not tamper with the high pressureswitch. If the compressor does not turn off at 10 bar gauge or the safety valve(21)vents at 11bar gauge for ANY reason press the red compressor ON/OFF switch(34) immediately and

vent the receiver by opening the receiver discharge/vent valve(32).The unit should then beinvestigated by a qualified engineer.

6. Do not tamper with the 2nd stage safety valve(21)or 1ststage safety valve(19) or allow

students to tamper with the safety valves.7. The motor and compressor pulleys and belt are covered with a safety cover. The unit MUST

NOT be operated with this removed. Prevent students from attempting to insert anything intoair vent grilles or apertures adjacent to pulleys and the motor cooling fan.

8. If the RCCB or overload cut outs inside the control console operate for any reason the unitshould be investigated by a qualified electrician.

It is recommended that the internal RCCB press to test is pressed periodically or at intervalsspecified by local regulations. As this must be tested with the control console cover removedand the electrical power on this should only be undertaken by a qualified electrician. If the

device does not trip when tested the unit should be investigated by a qualified electrician.9. Depending upon local regulations the outlet air vessel may require inspection by a competent

authority.

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OPERATING PROCEDURES

Please refer to the Schematic Diagrams on page 1, 2, 3 and 4

It is assumed that the Installation procedures detailed on page 6 onwards have been carried out and that

the compressor module is connected to the control console and its instrumentation. If the optional

computerised data acquisition upgrade FC865A has been purchased operation of this is dealt with in a

separate section. The operation of the F865 unit however remains the same.

Ensure that the Precautions and Warnings detailed on page 17 have been read, understood and

explained to the students/operators.

Starting and Maintaining Stable Conditions as a Two Stage Compressor

1. Ensure that the and receiver discharge /vent valve (32)is fully open. Check that the drain

valve at the base of the outlet air receiver(27)is closed.

2. Fully open valve A(24)(turn anti-clockwise) and fully close valve B(25)(turn clockwise).

3. If intercooling is to be used turn on the local water supply and open the valve on the cooling

water flowmeter(16). If Intercooling is not required close the cooling water flowmeter(16)

valve fully.

4. Adjust the orifice plate manometer(4) scale to zero. Turn on the main switch(1) on thecontrol console and the instruments will illuminate.

5. Ensure that the motor belt cover is fully secure.Ensure that the compressor has oil in its

sump.

6. Finally press the green compressor ON switch(33) on the high pressure switch(34) onthe compressor module and the compressor will start.

Air should be heard venting from the receiver discharge/vent valve(32) AND from

the high pressure switch area. This is normal. The high pressure switch also activatesa compressor unloading device to aid starting when the outlet air receiver(27)is at

high pressure. Ensure that the motor tachometer(3) indicates the motor speed and that theorifice plate manometer(4) shows a positive differential pressure.

7. Most tests involve adjusting the discharge pressure to a set value and maintaining thisuntil all readings (including temperatures) are stable and recording the data. To increasethe discharge pressure close the outlet receiver discharge/vent valve(32) fully and air willbe heard venting from the high pressure cut out and the non-return valve on the 2ndstageair receiver(27). The 2ndstage pressure gauge(20)will show a slowly rising pressureuntil at approximately 100kN/m2 the automatic vent closes and the pressure will start to

rise faster.8. When the pressure has reached the desired level slowly open the receiver discharge/ventvalve(32) until the pressure is stable. This may take several attempts. There is a delay ofseveral seconds after each adjustment has an effect on the discharge pressure.

Adjustment or Removal of Intercooling Effect

9 The amount of intercooling on the F865 is controlled by the cooling water flowmeter(16)

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MAXIMUM OPERATING PRESSUREThe maximum pressure that can be sustained is approximately 10 bar gauge as this is the setpressure of the high pressure cut out. The actual value can only be determined by experimentas the setting will vary slightly from machine to machine.

If the unit cuts out on the high pressure cut out then the pressure in the outlet airreceiver(27). will have to be allowed to fall until the compressor re-starts automatically.

Starting and Maintaining Stable Conditions as a Single Stage Compressor

1. Ensure that the and receiver discharge /vent valve (32)is fully open. Check that the drainvalve at the base of the outlet air receiver(27)is closed.

2. Fully close valve A(24)(turn clockwise) and fully open valve B(25)(turn anti-clockwise).

3. There is no intercooling function in single stage operation

4. Adjust the orifice plate manometer(4) scale to zero. Turn on the main switch(1) on the

control console and the instruments will illuminate.5. Ensure that the motor belt cover is fully secure. Ensure that the compressor has oil in its

sump.6. Finally press the green compressor ON switch(33)on the high pressure switch(34) on

the compressor module and the compressor will start.Air should be heard venting from the receiver discharge/vent valve(32)AND from the

high pressure switch area. This is normal. The high pressure switch also activates acompressor unloading device to aid starting when the outlet air receiver(27)is at highpressure.

1. Ensure that the motor tachometer(3) indicates the motor speed and that the orifice platemanometer(4)shows a positive differential pressure.

7. Most tests involve adjusting the discharge pressure to a set value and maintaining thisuntil all readings (including temperatures) are stable and recording the data. To increasethe discharge pressure close the outlet receiver discharge/vent valve(32) fully and air willbe heard venting from the high pressure cut out and the non-return valve on the 2ndstage

air receiver(27). The 2ndstage pressure gauge(20)will show a slowly rising pressureuntil at approximately 100kN/m

2 the automatic vent closes and the pressure will start to

rise faster.8. NOTE that the MAXIMUM operating pressure in single stage mode is approximately

350kN/m2 as the large diameter 1st stage cylinder is not designed for high pressure

operation. The 1st stage safetyvalve(19) will vent at approximately 4000kN/m2. Do notattempt to exceed this pressure or damage to the compressor may result.

9. When the pressure has reached the desired level slowly open the 2ndstage discharge/vent

valve(32) until the pressure is stable. This may take several attempts. There is a delay ofseveral seconds after each adjustment has an effect on the discharge pressure.

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Stopping and Shutting Down1. In the event that the compressor has to be stopped in an emergency press the red

compressor OFF/Stop switch(34)on the high pressure switch(35)2. To shut down the compressor normally slowly open the receiver discharge/vent

valve(32)and allow the outlet air receiver to vent. While the receiver is still under pressurealso open the drain valve located under the receiver. This will allow any condensate in thereceiver to vent and reduce the possibility of corrosion.

3. When the unit is back to atmospheric pressure, press the red press the red compressorOFF/Stop switch(34) on the high pressure switch(35) and then turn off the main

switch(1)on the control console.4. Finally it is recommended that the unit is isolated from the local electrical supply and

water supply to prevent inadvertent operation.

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MAINTENANCE

Compressor Module- After each use open the drain valve on the outlet receiver to vent any condensate.- Ensure the oil level shows in the compressor sight glass.

The sight glass and filler are visible in the above picture.- If the level is low add SAE 40 mineral oil only by unscrewing the filler plug.- If it is ever necessary to drain the compressor the drain plug is below the sight glass.- Ensure that the cylinder head bolts are tight. The maximum torque is 25Nm.- The belt tension must not allow the belt to slip. The belt should have a flex of

approximately 10mm (0.5 inch) . To adjust the belt it is necessary to remove the beltguard and then loosen the bolts securing the plate holding the motor support bearings.

- Always replace and secure the belt cover after adjusting the belt. Do not run the unit

with the belt cover removed.

Control Console

- Periodically check the operation of the internal RCCBat the rear of the controlconsole or at intervals specified by local safety regulations. As this must beundertaken with the cover removed and the power on it should be carried out by aqualified person. Press the press to test button and the unit should turn off the power.If it does not then the unit should be checked by a competent electrician.

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USEFUL DATA

Compressor Dimensions

Cylinders 2

Low Pressure Cylinder

Bore 95mm

Stroke 50mm

High Pressure Cylinder

Bore 50mm

Stroke 50mm

Swept Volume per revolution 0.3544 x 10-3m3

Specific Heat of Water34.18 10Cp= J/kgK

Air Flow Measurement

( )55.670 10 1 273.15vq h t= +

Where vq = Air flow volume m3/second

h = Orifice plate manometer pressure mmWg

Temperature Measuring points

t1 Air into 1ststage cylinder (ambient temperature)

t2 Air leaving 1ststage Cylinder (before intercooler)

t3 Air entering 2ndstage cylinder (after intercooler)

t4 Air leaving 2

nd

stage cylindert5 Water into intercooler

t6 Water leaving intercooler

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EXPERIMENTAL PROCEDURESThe following detail suggested experimental procedures for the Two Stage e Compressor Test unit F865

If the optional Computerised Data Acquisition Upgrade FC865A has been purchased the operating

procedures for the F865 are identical except that data may be recorded continuously or at discrete

intervals using the software. The procedures for software operation are detailed elsewhere in this manual.

1. Investigation of Variation in Air Flow Rate With Compressor Pressure Ratio:-

With and without intercooling

2. Investigation of Variation in Volumetric Efficiency with Compressor Pressure Ratio. With and

without intercooling.3 Investigation Of Variation Of Isothermal Efficiency With Compressor Pressure Ratio. With

and without intercooling.4 Investigation Of The Compressor Performance Relative To Electrical Power, Shaft Power,

And Heat Loss. With and without intercooling.

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ObservationsWITH INTERCOOLINGAmbient Pressure 1.01 Bar (1.010 x 105N/m2)

Sample No.1 2 3 4 5 6 7 8 9 10 11 12

Inlet Temperaturet1 /C 22.5 23.2 23.8 24.3 24.2 24.3 24.3 24.4 24.5 24.6 24.6

Air out of 1ststage

t2 /C 136.3 147.2 151.6 154.8 155.7 157.9 159.2 160.8 162.7 163.6 162Air into 2ndstage

t3 /C 37.6 41.1 42.6 43.7 43.8 44.1 44.1 44.3 44.5 44.6 38.1

Air out of 2ndstaget4 /C 68.6 83.6 94.8 109.1 115.4 125 131.7 138.9 145.1 146.9 144.1

Water Inlett5 /C

13.1 14 14 14.4 14.3 14.5 14.4 14.4 14.6 14.5 13.1

Water Outlett6 /C 20.8 22.1 22.4 22.9 23.1 23.3 23.3 23.3 23.2 23.6 17.4

1ststage Pressurep1 / kN/m

2 220 250 260 260 270 280 280 280 300 300 300

2ndstage Pressurep2 / kN/m2 100 200 280 440 500 600 680 800 900 960 900

Manometer Heightf / kg 69.6 66.4 64.8 60.9 60.1 60.1 59.3 58.5 58.5 57.7 58.5

Motor VoltsV / Volts 420 420 420 418 410 410 410 410 410 410 415

Compressor SpeedNc / rpm 1380 1370 1360 1360 1350 1360 1360 1350 1340 1350 1340

Cooling Water Flowwm& /g/s 20 20 20 20 20 20 20 20 20 20 20

Compressor CurrentI / Amps 5.5 5.7 6 6.2 6.5 6.6 6.8 6.9 7 7 7

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26

Inlet Absolute Pressure Pi

5

3 2

0 1.01 10

101 10 N/m

AmbientPi pi P= += +

=

Similarly 1ststage Outlet Pressure

1 1

3 5

3 2

260 10 1.01 10

361 10 N/m

AmbientP p P= +

= +

=

Similarly 2nd

stage Outlet Pressure

2 2

3 5

3 2

440 10 1.01 10

541 10 N/m

AmbientP p P= +

= +

=

1ststage Pressure ratio

31

3

361 10

101 10

3.57

i

P

P

=

=

2nd

stage Pressure ratio3

2

31

541 10

361 10

1.49

P

P

=

=

Overall Pressure Ratio3

2

3

541 10

101 10

5.37

i

P

P

=

=

By repeating the calculations on the remaining data the parameters may be presented graphically. A typicalgraph is shown on the following page

If th d i t d ith th i t li di bl d th diff t t f lt b bt i d

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27

Ov

FirstStage

Pressure

Ratio

Second

Stage

Press

ure

TwoStageCo

mpression

WithIntercoo

ling

Volume Flow L/s

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28

Observations

WITHOUT INTERCOOLINGAmbient Pressure 1.01 Bar (1.010 x 105N/m2)

Sample No.1 2 3 4 5 6 7 8 9 10 11 12

Inlet Temperaturet1 /C 25 25.1 25.4 25.3 26 26.4 26.4 26.6

Air out of 1ststage

t2 /C 154.2 158.2 164.1 167.2 170.4 171.4 176.3 177.2

Air into 2ndstage t3 /C 137.1 143.8 148.5 151.2 154.6 155.9 160 161

Air out of 2nd

staget4 /C 103.9 114.7 126 139.1 149.8 158.6 174.4 176.9

Water Inlett5 /C - - - - - - - -

Water Outlett6 /C - - - - - - - -

1ststage Pressure

p1 / kN/m

2

250 280 300 320 320 320 330 3402ndstage Pressure

p2 / kN/m2 100 200 280 400 510 600 740 800

Manometer Heightf / mm 61.7 60.1 58.5 56.9 56.1 55.7 54.5 53.7

Motor VoltsV / Volts 420 420 420 420 420 420 420 420

Compressor SpeedNc / rpm 1370 1370 1360 1360 1360 1360 1350 1350

Cooling Water Flowwm& /g/s 0 0 0 0 0 0 0 0

Compressor CurrentI / Amps 5.7 5.8 6 6.3 6.5 6.7 7 7.1

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29

Volume Flow L/s

TwoStag

eCompression

WITHOU

TIntercooling

Second

Stage

PressureRatio

FirstSstage

PressureRatio

OvPr

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30

It can be seen from the graph on page 27 that, as the overall pressure ratio increases the volume flowdecreases.

The reduction in air flow rate is partially due to the clearance volume that must be left at the top of both the

low pressure and high pressure cylinder to allow room for the inlet valves to operate.

For economy and simplicity of operation these valves are usually spring steel and so require some pressuredifferential in order to open. Similarly the discharge valves are also spring steel and require a differentialpressure across them to remain open.

For the above reasons a significant amount of air at or above the discharge pressure is left in the cylinder atthe end of each discharge stroke.

Hence as the discharge pressure (or pressure ratio) is increased the volume flow rate of the air through thecompressor decreases.

The effect of the intercooling is to reduce the volume (increase the density) of the air between the lowpressure and high pressure cylinder. The effectiveness of the intercooling is illustrated by the graph on page

29 showing a similar test but without intercooling. This shows similar test conditions to the results onpage 27 but the volume flow is substantially reduced at similar pressure ratios due to the air between stagesbeing at very high temperatures and hence a low density.

The significant difference between the single stage and two stage compressor is not only the effective airvolume flow arte but also the effect of the intercooling on the power required to drive the compressor. Thisis demonstrated in later experiments.

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31

2 INVESTIGATION OF VARIATION IN VOLUMETRIC EFFICIENCY WITHCOMPRESSOR PRESSURE RATIO:- With and Without Intercooling

.

Experimental Procedure

The experimental procedure for this experiment is identical to that used for experiment No1 on page 24.

The data collected is identical to experiment No 1 and therefore the data from this may be used in this

procedure.

Typical observations are shown on page 25

The data shown on page 25 was collected with the intercooler operating. It is recommended that theprocedure is repeated with the intercooler disabled following the procedure on page 18.Typical data with the intercooler inoperative is given on page 28.

Sample Calculations.

Air flow rateFrom Useful Data on page 22

( )55.67 10 1 273.15vq h t= + Where vq = Air flow volume m3/second


For observation No 4 on page 25

( )( )

5

5

3

5.67 10 1 273.15

5.67 10 60.9 24.3 273.15

0.00763 m /

7.63 l/s

vq h t

s

= +

= +

=

=


5

3 2

0 1.01 10

101 10 N/m

AmbientPi pi P= +

= +

=


1 1 AmbientP p P= +

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32


31

3

361 10

101 10

3.57

i

P

P

=

=

2nd


2

31

541 10

361 10

1.49

P

P

=

=


2

3

541 10

101 10

5.35

i

P

P

=

=

From Useful Dataon page 22 the compressor swept volume per revolution 0.3544 x 10-3

m3 or

0.3544 litre

From the sample data on page 25 , observation No 4

The measured compressor speed Nc = 1360rpm

Hence the volume swept by the compressor at this speed is.

0.3544 1360Swept Volume Vs =

60

8.033 Litres/second

=

For a perfect compressor , with no clearance volume at the top of the cylinder and no throttling at the inlet

or discharge valves this would be the maximum air flow rate through the compressor. However as

demonstrated in experiment No 1 the volume decreases with increasing pressure ratio.

Therefore comparing the swept volume with the actual volume is a method of describing the efficiency of

the compressor. As a non-dimensional parameter this can be used to compare similar compressors.

Volumetric Efficiency

ActualVolume Swept Per cycle

Swept VolumeVol

qv

=

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33

WITHOUT

INTERCOOLING

WIT

H

INT

ERCOOLING

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34

The reduction in volumetric efficiency is caused by the same parameters detailed at the completion of

experiment No. 1. However as the parameters are non-dimensional the data may be used to comparecompressors in order to assess their performance.

It can also be seen from the graphical data that the intercooler increases the volumetric efficiency under all

conditions. This is also due to the increase in air density between stages due to the cooling of the air.

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35

3 INVESTIGATION OF VARIATION OF ISOTHERMAL EFFICIENCY WITH

COMPRESSOR PRESSURE RATIO:- With and Without Intercooling




procedure.


The data shown on page 25 was collected with the intercooler operating. It is recommended that theprocedure is repeated with the intercooler disabled following the procedure on page 18.

Typical data with the intercooler inoperative is given on page 28.

THEORYThe pressure volume diagram for the air in the cylinder of an ideal compressor is shown below.

The constant pressure line a-b represents the induction, inlet, or suction stroke. The air is then compressed

adiabatically 1.4 Constantpv = as shown by the curve b-c and the air is forced out of the cylinder atconstant pressure shown by the line c-d. As the piston moves downward any air remaining in the clearance

volume of the cylinder expands along the line d-a.

The work done on the air is the area is represented by the area abcd.

p

v

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36

It can be shown that the work required for adiabatic compression is

Where i = inlet condition, o= outlet condition1

1

11

Or, as

11

oAdiabatic air i i

i

i i i

oair i

i

PW m P v

P

P v RT

Pm RTP

=

=

=

&

&

Similarly for adiabatic compression

1

o i

i

PoT T

P

=

In the case of isothermal compression o iT T=

For the ideal case of isothermal compression

1 onstantpv C= it can also be shown that:

ln

ln

oIsothermal air i i

i

oair i

i

PW m P v

P

or

Pm RT

P

=

=

&

&

In order to reduce the work required to a minimum various methods have been used to try and make thecompression process approach the isothermal line. These include water injection to cool the air, watercooling of the cylinder or air cooling of the cylinder. In addition it is possible to approach isothermal

compression by dividing the compression into two or more stages and cooling the air between stages usinga heat exchanger. This is the procedure adopted in the Hilton F865 Tow Stage Compressor Test Unit

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37

Note that the expansion of the clearance volume in the two cylinders will also be separated but this has notbeen shown for simplicity.

To give a measure of the thermodynamic efficiency of a compressor a useful term is the isothermalefficiency.

This is the ratio

Isothermal Work

Actual Work

ln

Isothermal

Isothermal

Actual

oair i

i

Actual

W

W

Pm RT

P

W

=

=

=

&


For a compressor with Intercooling

Air flow rate

From Useful Data on page 22

( )55.67 10 1 273.15vq h t= + Where vq = Air flow volume litres/second


1t = Air inlet temperatureC

From the test data on page 25, for observation No 5

( )

( )

5

5

3

5.67 10 1 273.15

5.67 10 60 24.2 273.15

0.0075m /

7.5 Litre/s

vq h t

s

= +

= +

=

=

The air density Air can be determined using the perfect gas law

iAir

i

P

RT =

Where iP = Inlet Air Pressure iT = Intake Temperature T1

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38

Similarly 2ndstage Outlet Pressure

2 2

3 5

3 2

500 10 1.01 10

601 10 N/m

AmbientP p P= += +

=


31

3

371 10

101 10

3.67

i

P

P

=

=

2nd


2

31

601 10

371 10

1.62

P

P

=

=


2

3

601 10

101 10

5.95

i

P

P

=

=

From sample data on page 25, for observation No 5 t1 = 24.2C

Hence

( )

5

3

3

1.01 10

287 24.2 273.15

1.18 kg/m

1.18 10 kg/Litre

iAir

i

P

RT

=

=

+

=

=

Hence the mass flow of air

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39

If it is assumed that the first stage compression is adiabatic then

For adiabatic compression

1

1

1

2 1

o i

i

i

PoT T

P

or

P

T T P

=

=

For the first stage compression (sample No 5 page 25) the pressure ratio1

3.67i

P

P= , 1T = 24.2C, =1.4

( )

1

12 1

1.4 11.4

o

o

(24.2 273.15) 3.67

431.2

431.2 273.15

158.0

i

PT T

P

K

C

C

=

= +

=

=

=

Referring to sample No 5 page 25, the recorded T2 = 155.7 C

Therefore the first stage compression may be assumed to be adiabatic.

The adiabatic work required for compression

1

1

11

11

11

oAdiabatic air i

i

air

i

PW m RT

P

Pm RT

P

=

=

&

&

Substituting for known values1

P

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41

Substituting for known values

( ) [ ]

1

23

1.4 13

1.4

11

1.48.87 10 287 43.8 273.15 1.62 1

1.4 1

418

Adiabatic air

iPW m RT P

Watts

=

= +

=

&

The sum of the work required for both stages is therefore

1195.8 418

1613.8

TotalW

Watts

= +

=

The isothermal work required for compression in the two stages.

1 21 3

1

ln lnIsothermal air airi

P PW m RT m RT

P P

= +

& &

Substituting for known values

( ) ( ) ( ) ( )3 38.87 10 287 24.3 273.15 ln 3.67 8.87 10 287 43.8 273.15 ln 1.62

987 389

1376

IsothermalW

Watts

= + + +

= +

=

A measure of the efficiency of the compression process

Isothermal Work

Actual Work

1376100%

1613

85.3%

Isothermal

Isothermal

Actual

W

W

=

=

=

=

The effect of the intercooling can be seen more readily if the calculations are repeated for tests undertaken

WITHOUT the intercooler operating.Examining the test data on page 28 sample No 5 which was recorded at a similar second stage pressure

(510kN/m2).

The equivalent calculations give the following results.1 1

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42

The above figure compares with 1613 Watts for the unit with the intercooling in operation. The

intercooling does reduce the overall power requirement slightly but its major effect is the increase involumetric efficiency.

It can be shown that for a two stage compressor the optimimum condition is where the total work

requirement is shared equally between the two stages. From the equations this condition will exist when

1 2

1i

P P

P P

=

For this compressor this condition does not exist as in the above sample result from page 28 sample No 5

1

2

1

4.17, 1341

1.45, 427

LP

i

HP

PW Watts

P

PW Watts

P

= =

= =

It is evident that the pressure ratio could be changed in this case to reduce the overall work input but of

course this would be a design change to the compressor.

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43

4 INVESTIGATION OF THE COMPRESSOR PERFORMANCE RELATIVE TOELECTRICAL POWER:- With and without Intercooling

.




procedure.


The data shown on page 25 was collected with the intercooler operating. It is recommended that theprocedure is repeated with the intercooler disabled following the procedure on page 18.Typical data with the intercooler inoperative is given on page 28.


Air flow rateFrom Useful Data on page 22

( )55.67 10 1 273.15vq h t= + Where vq = Air flow volume litres/second


1t = Air inlet temperatureC

From the test data on page 25, for observation No 5

( )

( )

5

5

3

5.67 10 1 273.15

5.67 10 60.1 24.2 273.15

0.00757 m /

7.58 Litre/s

vq h t

s

= +

= +

=

=

Due to the design of the orifice plate the inlet pressure iP is very close to ambient pressure PInlet Absolute Pressure Pi

50 1.01 10

AmbientPi pi P= +

= +

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44


2

3

601 10

101 10

5.95

i

P

P

=

=

From Useful Dataon page 22 the compressor swept volume per revolution 0.3544 x 10-3

m3

or0.3544 litre





607.97 Litres/second

=






Volumetric Efficiency

ActualVolume Swept Per cycle

Swept Volume

7.56

100%7.97

94.8%

Vol

s

qv

V

=

=

=

=

The electric motor on the compressor is a 3 phase device

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45


V=410 Volts I = 6.5 Amps.

Hence

3 418 6.2 0.9

3815

ElectricalW

Watts

=

=

This value may be compared with the calculated work from the previous experiment at the same testconditions. The calculated work input based upon the compressor pressure ratios , temperatures and airflow rate was

1168.9 409

1577.9

TotalW

Watts

= +

=

This is approximately 40% of the electrical power input and indicates the magnitude of frictional losses

in the belt drive and compressor and electrical losses in the motor.

Repeating the above calculations for all of the test data on page 25 where the intercooler is in use and forthe test data on page 28where the intercooler is not used results in a graph as shown on the followingpage .

It can be seen that with the intercooler the volumetric efficiency is higher for the same pressure ratio and

the electrical power input is lower, particularly at high pressure ratios.

Considering that most air compressors of this type are used on a continuous basis the saving in electricalpower can be considerable.

46

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46

47

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47

5 OPERATION OF THE COMPERSSOR AS A SINGLE STAGE DEVICE

.

Experimental ProcedureIt is assumed that the unit has been installed and configured following the procedures detailed on pages6 onwards. The unit will be operated as a single stage machine and in order to do this it must be startedfollowing the procedure on page 19, Starting and Maintaining Stable Conditions as a Single StageCompressor

In single stage use only the larger low pressure cylinder passes air and the high pressure cylinder and

intercooler are bypassed. Due to the valve arrangement there is no air flow at all through the high pressure

cylinder and hence the overall work input to the high pressure stage will be friction effects, assuming thatany air trapped in the high pressure cylinder compresses and expands adiabatically and reversibly.

Due to the pressure limitations of the low pressure stage the range of operation must be restricted to an

upper 4 Bar limit.

First record the local ambient air pressure AmbientP using a barometer or obtain this from meteorologicalsources.

1. Ensure that the receiver discharge/vent valve(32)is also fully open. Record the data shown on

page51.2. Increase the outlet pressure to approximately 100-150kN/m2by closing the receiver

discharge/vent valve(32) following the procedure shown on page 18 onwards. Note that the

actual pressure is not important and that the minimum operating pressure will depend upon the

individual machine characteristics. The pressure at which the vent valve closes will vary from

machine to machine.3. Repeat the above readings.

4. Increase the outlet pressure by convenient amounts (e.g. 50 or 100kN/m2) and repeat the

observations. Note that the maximum operating pressure in single stage operation will be limited

by the low pressure safety valve which is set at 4 Bar gauge pressure. If the relief valve vents then

reduce the pressure by opening the receiver discharge/vent valve(32).

5. As with the minimum pressure the exact maximum operating pressure will vary slightly from

machine to machineTypical test results are shown on page 51.


Air flow rate

From Useful Data on page 22

( )55 67 10 1 273 15vq h t= +

48

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48

From Useful Dataon page 22 the compressor swept volume per revolution 0.3544 x 10-3 m3 or

0.3544 litreFrom the sample data on page 51 , observation No 5




60

8.092 Litres/second

=






Volumetric EfficiencyActualVolume Swept Per cycle

Swept Volume

7.1100%

8.092

87.7%

Vol

s

qv

V

=

=

=

=


5

3 2

0 1.01 10

101 10 N/m

AmbientPi pi P= +

= +

=


1 1

3 5400 10 1.01 10

AmbientP p P= +

= +

49

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49

The active power of a 3 phase motor can be determined from

3ElectricalW V I Cos=

The derivation of the above equation is beyond the scope of this manual but should be found in mostelectrical engineering text books.

From the sample data on page 51 , observation No 5V=420 Volts I = 5.8 Amps.

Hence

3 420 5.8 0.9

4019

ElectricalW

Watts

=

=

Repeating the above calculations the data may be plotted on a graph as shown on page 50. The data from asimilar overall pressure ratio range has been added to the graph and it can be seen that the addition of thesecond stage with intercooling greatly increases the volumetric efficiency and reduces the powerconsumption.

However it should be noted that the two stage compression is only beneficial providing the second stage

compression pressure is higher than tne first stage. This will normally be the case if the compressor iscorrectly sized for the duty(air consumption) and is operating in an industrial situation where the receiver isoperating at or near maximum pressure.

50

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51

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Observations

SINGLE STAGEAmbient Pressure 1.01 Bar (1.010 x 105N/m2)

Sample No.1 2 3 4 5 6 7 8 9 10 11 12

Inlet Temperaturet1 /C 20.6 21.3 21.9 22.2 22.6

Air out of 1ststaget2 /C 107.9 130.3 143.6 150.3 160

Air into 2ndstaget3 /C 38.6 41.2 42 42.2 4203

Air out of 2ndstaget4 /C 35.5 44.3 51.8 55.6 50.6

Water Inlett5 /C

- - - - -

Water Outlett6 /C - - - - -

1

st

stage Pressure p1 / kN/m2 120 220 300 380 400

2ndstage Pressurep2 / kN/m2 100 200 300 380 400

Manometer Heightf / kg 71.1 66.4 60.1 55.3 54.5

Motor VoltsV / Volts 420 420 420 420 420

Compressor SpeedNc / rpm 1390 1380 1380 1370 1370

Cooling Water Flowwm& /g/s 0 0 0 0 0

Compressor CurrentI / Amps 5 5.4 5.6 5.7 5.8

52

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Observation Sheet F865 Two Stage Compressor Test Unit

Operating Condition (delete as appropriate)*SINGLE STAGE TWO STAGE WITH INTERCOOLING TWO STAGE WITHOUT INTERCOOLING

Ambient Pressure

Sample No.1 2 3 4 5 6 7 8 9 10 11 12

Inlet Temperaturet1 /C

Air out of 1

st

stage t2 /C

Air into 2ndstaget3 /C

Air out of 2ndstaget4 /C

Water Inlett5 /C

Water Outlett6 /C

1ststage Pressure

p1 / kN/m2

2nd

stage Pressurep2 / kN/m

2

Manometer Heightf / kg

Motor VoltsV / Volts

Compressor Speed Nc / rpm

Cooling Water Flowwm& /g/s

Compressor CurrentI / Amps

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