1 pressure measurement bench

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1 Pressure Measurement Bench

TThe equipment described in this manual is

manufactured and distributed by

TECQUIPMENT UMITED

Suppliers of technological laboratoryequipment designed for teaching.

BONSALL STREET, LONG EATON, NOTTINGHAM, NG10 2AN, ENGLAND.

Tel: +44 (0)115 9722611 : Fax: +44 (0)115 9731520r E-Mail: General Enquiries: CompuServe, mhs:sales@tecquip : Internet, [email protected]: Parts &. Service: CompuServe, mhs:service@tecquip : Internet, [email protected]

Information is available on the Internet at: http:/ /www.tecquip.co.uk-

e TecQuipment Limited

No part of this publication may be reproduced or transmittedin any form or by any means, electronic or mechanical,including photocopy, recording or any information storageand retrieval system without the express permission ofTecQuipment Limited. Exception to this restriction is given tobona fide customers in educational or training establishmentsin the normal pursuit of their teaching duties.

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Whilst all due care has been taken to ensure that the contentsof this manual are accurate and up to date, errors or omissionsmay occur from time to time. If any errors are discovered inthis manual please inform TecQuipment Ltd. so the problem

may be rectified.

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A Packing Contents List is supplied with the equipment andit is recommended that the contents of the package(s) arecarefully checked against the list to ensure that no items aremissing, damaged or discarded with the packing materials.

In the event that any items are missing or damaged, contactyour local TecQuipment agent or TecQuipment direct as soon

as possible.

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TECQUIPMENT H30 PRESSURE MEASUREMENT BENCH

CONTENTSI PAGESECI10N

~ 1.0 1

2

2

2

3

1.1

1.2

1.3

1.4

1

INTRODUCflONInstallation and PreparationCalibration of a Pressure Gauge UnitManometer and Gauge FrameworkRoutine Care and Maintenance

14

4

5

2.01 2.1

2.2

EXPERIMENTAL PROCEDURE

Pressure Gauge Dead Weight Tester

Pressure Measurement

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6

7

.:J.u

3.1

3.2

RESULTS AND CALCULA nONSPressure Gauge Dead Weight TesterPressure Measurement

[ 4_0 DISCUSSION OF RESULTS 9

5.0 QUEsnONS FOR FURTHER DISCUSSION 10

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SEC'fION 1.0 INTRODUC'fION

.1

~ PressureGauge""e Ie e

e

VacuumGauge

eInclined 'U' Tube

Manometer

Vertical 'U' TubeManometerl1J ~r r---

~~

Figure 1 H30 Pressure Measurement Bench

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The apparatus consists of a steel framework/bench construction with verticaland inclined manometers, and Bourdon type pressure gauges. Varioussockets are situated adjacent to the gauges and manometers allow directconnection to same, as tees and tubing are supplied to allow construction ofvarious permutations. The pressure and vacuum are controlled by fine

adjustment of the syringe assembly.

r Manometry is a fundamental method of measuring low pressure and,together with Bourdon type gauges, is used to a great extent in engineeringpractice. The unit for calibration of a pressure gauge can be sited on the tabletop, and with its perspex dial face allows the workings of a Bourdon tube tobe studied. All the gauges used on the equipment are of this type, having acircular arc movement encompassing approximately 270°. The Bourdon tube

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is rigidly held at one end and, when a pressure is admitted, a straightening ofthe tube takes place which is related through a mechanical system to allowproportional movement of the dial around the graduated scale. The range ofthe gauge depends on the type and thickness of the material used for the

Bourdon tube.

When it is desired to check the accuracy of the Bourdon gauge, the usualprocedure is to load it with known pressures by means of a dead weighttester using oil or water to transmit the pressure. The equipment also allowsa comparison between a Bourdon gauge and a manometer to be considered.

Installation and PreparationLl

Immediately upon receipt of the apparatus, all components should bechecked against the accompanying PACKING CONTENTS LIST. If any itemsappear to be missing a careful check should be made amongst all packingmaterials.

Calibration of a Pressure Gauge Unit1.2

Set out the apparatus on a level worktop and remove the piston from thepressure gauge dead weight tester; it is delivered lightly oiled, and should bewiped only when the unit is to be used. Fill the cylinder with water, andremove the trapped air in the transparent tube by tilting the unit and gentlytapping it. A small amount of air in the system will not affect the experimentor results. Top up the water and insert the piston into the cylinder, allowingair and excess water to discharge through the top hole of the cylinder. Allow

the piston to settle.

Manometer and Gauge Framework1.3

To fill the vertical and inclined manometers of the main unit, firstly loosenthe two artery clamps situated at the top of each manometer on the panel. Afunnel (supplied) can now be inserted into each tube and water can then bepoured in (red colouring can be added to the water at a ratio of 50:1 to


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improve clarity). To assist in the filling a second artery clamp is provided,which should be used to close the tube fitted, from the manometer beingfilled, to the relevant tube coupling; this will stop the water dischargingthrough to the coupling during filling. Enough fluid should be put into thetubes to half fill each manometer. On completion, close the two clamps onthe front panel and remove the artery clamps.

Note: It may be necessary to tap the tubes whilst fitting to allow trapped air

to escape.

1.4 Routine Care and Maintenance

After use, wipe the unit with a dry cloth. The pressure gauge calibration unitshould be drained and the piston and cylinder dried with a lint free cloth.The piston should then be lightly smeared with oil and refitted to the cylinderto prevent damage. This is most importanL

If the piston becomes seized in the cylinder, use a penetrating oil and apply toboth inlet and outlet, allowing time for the unit to soak thoroughly. Use atwisting action after 3 to 4 hours to remove the piston. Do not attempt toclean the piston or cylinder with any harsh abrasive. Use only a mixture ofpowdered chalk and oil to remove any discoloration.

After a period of time, the fluid may discolour; if SO, this can be emptied byturning the unit on its side and refilled as explained earlier in Section 1.3.

To safeguard the pump from moisture, a small fluid trap is fitted to the inletand outlet at the pump; this must be emptied if there is any trace of fluid

showing.

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TECQUIPMENT H3O PRESSURE MEASUREMENT BENCH

SEcrION 2.0 EXPERIMENTAL PROCEDURE

Weights Bourdontube

Overflowto waste 2

Pressure gaugecalibrated inkN/m

~~ /~2Z2 ~Piston

Gauge turnedthrough 90. to

show mechanism

Transparenttube

Figure 2 Pressure Gauge Calibrator

2.1 Pressure Gauge Dead Weight Tester

The cross-sectional area and the mass of the piston should be noted. Ensurethe cylinder is vertical. Masses are added in approximately eight incrementsup to a maximum of 5.2kg. On no account should more than the suppliedmasses be loaded. Always load the masses gradually, do not drop then ontothe platform. The pressure gauge reading should be recorded at eachincrement of loading. To prevent the piston sticking, rotate the piston gentlyas each mass is added. Reverse the above procedure, taking readings as themasses are removed.

.c'- TECQUIPMENT H30 PRESSURE MEASUREMENT BENCH';"c c

2.2 Pressure Measurement

~The syringe assembly can be plugged into either the respective gauge or themanometer. For vacuum tests the syringe should be fully depressed prior tofitting to the circuit. For pressure tests the syringe should be fully extendedbefore fitting to the system. By inserting a tee piece into the circuit, thepressure gauge and manometer may be used at the same time. Press the tubehome firmly to ensure a leakproof joint is made. When a suitable circuit is

complete, slowly move the syringe and note the change in both the gaugereading and manometer reading simultaneously. Carefully ensure the rangeof the manometer is not exceeded or fluid could be spilt.

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TECQUIPMENT H30 PRE~URE MEASUREMENT BENCH

SECTION 3.0 RESULTS AND CALCULA nONS

3.1 Pressure Gauge Dead Weight Tester

The actual hydrostatic pressure (P) in the system due to a mass of M kg(including the piston mass) applied to the piston is given by:

M x 9.81A

10-3 kN/m2p - x

2where A is the piston area in m

The observed and derived results are tabulated in the form of Table 1.

lncreasine: Pressure Decreasin2 PressureMass

added to

piston

Total mass

on piston

(M)

GaugeError

GaugeReading

GaugeError

Gauge

Reading

Actual

Pressure

(P)

kN/m2 kN/m2 kN/m2 kN/m2 kN/m2k~ kv;

Table 1 Results for Increasing and Decreasing Pressure(Calibration of Pressure Gauge)

From Table 1 graphs of the gauge pressure against actual pressure, and gaugeerror against actual pressure, should be plotted.


3.2 Pressure Measurement

Pressure Gaue:e §~~on Gau~eBourdon

Gauge

VerticallU1 Bourdon

Gauge

Vertical 'U'

tubetube

Inclined 'U'

tube manometer

ad1usted

Inclined IUII

tube manometer I

adjustedmanometer manometer

Amm H..Omm H.O I ~~..~ Amm H.. 0-

mm H~O mmH..O

0

50

100

150

200

250

300

350

400

0

-so

-100

-150

-200

-250

-300

-350

-400

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[Table 2 Results for Pressure Gauges, Suction Gauges and Manometers

PI

P2

Vertical 'U' TubeManometer

Inclined 'V' TubeManometer

Figure 3 Layout of IV' Tube Manometers

The inclined limb of the 'U' tube manometer is set at an angle of 54-. As aresult, direct comparison of the vertical manometer and pressure gauges canbe undertaken by simple trigonometry, to give adjusted readings, i.e. the

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TECQUIPMENT 1130 PRESSURE MEASUREMENT BENCH

adjusted reading of the inclined manometer for comparison to pressuregauges and the neutral 'U' tube is equal to the vertical limb reading minusthe inclined reading multiplied by sine 548.

PI Pu Pv= -

PuPI - P2-

Py Pt - P2 sin54=

where P g is gauge pressure; Puis vertical 'u' tube manometer pressure and P v

is the inclined 'u' tube manometer pressure.

From Table 2, a graph can be plotted showing the error on either the Bourdongauge or the manometer.

0 - . - . -150 200 250 300 350 400 4SO0 50 100

Pressure Bourden Gauge Reading (mm H2O)

Figure 4 Typical Calibration Graph of Bourdon Pressure Gauge andV erticallU1 Tube Manometer


SECfION 4.0 DISCUSSION OF RESULTS

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Two different kinds of error may normally be expected in a gauge of thistype. Firstly, there is the possibility of hysteresis, friction and backlash whichwill yield smaller gauge readings when the pressure is increasing than whenit is decreasing. Typically, the gauge tested on the calibration dead weighttester will have an error in the range of lkN/m2 of the entire range, which is

acceptably small. Secondly, there is error due to the scale being marked offincorrectly. It will be found that this error increases to a maximum of around2.5% of the full scale reading. This is acceptably small for many engineeringpurposes although gauges with an error of only 0.5% of the full scale reading

are commercially obtainable.T

Manometers also have an error due to inaccuracies in manufacturing the scale

and user error in reading the level of water.

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TECQUIPMENT H3O PRESSURE MEASUREMENT BENCH

SECI'ION 5.0 QUESnONS FOR FURTHER DISCUSSION

(1) What suggestions have you for improving the apparatus?

(2) No correction has been made to the results for the difference inelevation of the piston of the dead weight tester and of the pressuregauge. If the centre of the gauge were 200mm higher than the base ofthe piston, should a correction be made and, if so, how large would itbe?

(3) What alterations to the dimensions of the piston of the dead weighttester would you suggest if it were desired to calibrate a gauge havinga full scale reading of 3500kN/m2 using the same weights?

1 pressure measurement bench

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