Lab 1 Hydraulic

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Lab 1 Hydraulic

Transcript of Lab 1 Hydraulic

Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

1.0 Introduction The Bourdon pressure gauge, patented by the French engineer Eugene Bourdon in 1849, remains one of the most widely used gauges for measuring pressure in liquids and gases of many different types. It is a type of aneroid pressure gauge consisting of a flattened curved tube attached to a pointer that moves around a dial. The Bourdon pressure gauge as shown in figure below has three primary components which is a fluid that transmits the pressure, a weight and piston used to apply the pressure, and also an attachment point for the gauge to be calibrated. The weight applies a force over a precisely known area, therefore applying a known pressure to the fluid. The fluid is water that is essentially incompressible. Since a dead weight tester is relatively compact the effect of elevation changes on the pressure are negligible. The pressure at the piston face, therefore, is equal to the pressure throughout the water in the tester. A spill-pipe is fitted into the barrel which prevents the piston being ejected by excess pressure.

Figure 1: The Bourdon pressure gauge Since pressure is derived from force divided by area (F/A), the pressure generated by a dead weight tester is calculated by multiplying the mass by the acceleration due to gravity to determine the applied force, and then dividing this by the surface area of the piston cylinder. A piston cylinder assembly is mounted vertically to the top of the base and connected via manifolds and pipe work to the screw press or regulator. There are two1

Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

markings on the piston cylinder which indicate the region in which the weights must be floating and spinning before checking the reading of the device being calibrated. Some deadweight testers come with piston cylinders of different sizes which extend the range of the instrument to higher or lower set of pressures.

2.0 Objective of Experiment To calibrate a Bourdon type pressure gauge using a dead weight pressure gauge calibrator To study the importance of relative height between the dead weight tester and the gauge in calibration

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

3.0 Theoretical Background Bourdon pressure gauge is used to measure medium to very high pressures. The pressure to be measured is connected to the fixed open end of the bourdon tube. The applied pressure acts on the inner walls of the bourdon tube. Due to the applied pressure, the bourdon tube tends to change in cross section from elliptical to circular. This tends to straighten the bourdon tube causing a displacement of the free end of the bourdon tube.

To calibrate the gauge, we can add weights to a platform on a dead weight tester. The weights put a known force on to a piston. The piston has a known area, so we can calculate the pressure. A flexible tube containing water transfers the pressure on the piston to the Bourdon tube. By adding the weights in increments, we can record pressure readings from the gauge at each increment. They then remove the weights and record gauge readings. By working out theoretical results they can work out gauge error and discuss possible causes. This theory expressed as simply as force acting upon a known area. The pressure produced by pump is distributed by the manifold, to the base of precision machined piston and to a device being calibrated or checked. The preselected weights is loaded onto the piston platform are acted upon by gravity and develop a force that is to be equally opposed by the fluid pressure from the pump.

Pressure in exerted by water in the cylinder is

Where ( )

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

4.0 Experiment Setup 1. 2. 3. 4. 5. Hydraulic bench Dead weight pressure gauge calibrator Bourdon pressure gauge Weighs Water container

Figure: Dead Weight Pressure Gauge Calibrator

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

5.0 Methodology 1. The pressure gauge was placed on the bench top and it was connected inlet tube to the isolating cock on the gauge manifold. 2. A length of tube may be attached to the calibrator drain and laid into the channel to prevent spillage of water on to the bench top. 3. The calibrator is leveled by the adjusting feet whilst observing the spirit level. 4. The piston was removed and its mass was determined accurately. The masses of the calibration weights were determined accurately. 5. The control valves were closed on the bench. Both cocks operate pump starter were opened. 6. The valve was opened and water admitted to the cylinder. When full, close the valve on the bench, the pump was switched off. 7. Isolating cock was closed. 8. The piston was inserted and the piston was spin to minimize the effects of friction. Whilst the piston is spinning, the gauge reading was noted. 9. Procedure was repeated using different masses.

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

6.0 Flow Chart

Set up the apparatus

Attach a tube from the calibrator

Check the spirit level whether the calibrator is stable

Determine the mass of piston and masses of the calibration weights

Close control valves and open pump starter

Fill the cylinder with water until full

Close the valve, the isolating cock and the pump

Insert the piston and weights and spin it

Record the gauge reading whilst the piston is spinning

End

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

7.0 Result and Calculation Piston Mass (kg) Area of Piston ( x 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 244.8 244.8 244.8 244.8 244.8 244.8 244.8 244.8 244.8 20.037 40.074 60.110 80.147 100.184 120.221 140.257 160.294 180.331 20.000 39.000 58.000 75.000 98.000 118.000 140.000 160.000 182.000 0.037 1.074 2.110 5.147 2.184 2.221 0.257 0.294 2.331 0.185 2.754 3.638 6.863 2.229 1.882 0.184 0.184 1.281 ) Pressure in Cylinder (kN/ ) Gauge Reading (kN/ ) Absolute Gauge Reading = % Gauge Error

Table 1: Experimental Result

Pressure in Cylinder (kN/ 20.037 40.074 60.110 80.147 100.184 120.221 140.257 160.294 180.331 )

Gauge Reading (kN/ 20.000 39.000 58.000 75.000 98.000 118.000 140.000 160.000 182.000 Table 2: Accuracy of the Gauge )

Accuracy (%) 99.815 97.246 96.362 93.137 97.771 98.118 99.816 99.816 98.719

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

Calculation: Pressure in cylinder = (piston mass = (0.5 9.81) / area of piston

9.81) / 244.8

= 20.037 kN/m2 Absolute gauge reading = pressure in cylinder gauge reading = 20.037 20.000 = 0.037 kN/m2 Percentage gauge error = (absolute gauge error / actual pressure) = (0.037/ 20.037) = 0.185 % Accuracy/Efficiency = (gauge reading / pressure in cylinder) x 100% = (200 / 200.037) X100% = 99.815% *Calculation for the remaining values is carry out by using the same steps as shown at above. 100% 100%

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

Graph of Gauge Reading against Absolute Gauge Error200 Gauge Reading (kN/m2) 150 100 50 0 0.037 1.074 2.11 5.147 2.184 2.221 0.257 0.294 2.331 Absolute Gauge Error (kN/m2)

Figure: Graph of gauge reading against absolute gauge error.

Graph of Gauge Reading against Percentage Gauge Error200 180 160 140 120 100 80 60 40 20 0 0.185 2.754 3.638 6.863 2.229 1.882 0.184 0.184 1.281 Percentage Gauge Error (%) Gauge Reading (kN/m2)

Figure: Graph of gauge reading against percentage gauge error.

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Lab 1 Dead Weight Pressure Gauge Calibrator | Group 6

8.0 Discussion 1. Accoding to the plotted graphs of gauge reading against absolute gauge error, the pressure values obtained through calculations, it shows the deviation of the gauge readings of 0.037 kN/m2. In the other hand, the graph of gauge reading against percentage error has a little scattered trend compare to the previous graph. This may cause by errors and inaccuracies. The average gauge error is 0.185 %.

2. During the experiment, to reduce the effects of friction we spun the piston before pressure reading is taken. Due to the design of the apparatus, there is only a small gap between the cylindrical wall and the piston. If the cylindrical walls touch the piston, friction will be induced and hence the frictional force denoted will lower the force exerted on the liquid.

3. During the experiment, the thermal expansion will cause the size of the cylinder or piston to increase because there is a dissipation of energy in the fluid escaping between the piston and cylinder. Therefore, this will affect the effective area and the measured pressure will be different. Eventually will affect also the deviation of the experiment result from the theoretical result.

4. The dynamic viscosity of water at 25C is lower than oil. This shows tat water has a lower lubricating property compare to the oil. The irregularities on the surface of the piston and cylinder will produce a corkscrew effect when spun. This rotation is rised to a certain velocity to avoid any friction. But anyhow, friction will still exist and this will cause our reading of pressure to be inaccurate.

5. The Bourdon gauge has a glass cover plate so that the internal mechanisms can be seen. The pressure element is a curved, hollow metallic tube closed at on end, while the other end is connected to the pressure to be measured. The tube straightens out a small amount, pulling on a linkage to which is attached a pointer that moves across a metallic scale, this happen when the internal pressure is increased. The dial shows zero when the inside and outside of the bent tube are at the same pressure.

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Lab 1 Dead Weight