Dead weight piston gauge


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this report made by koya university student of chemical engineering (shwan sarwan ).

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Dead weight piston gauge

  1. 1. Koya University Faculty of Engineering, School of Petroleum & Chemical Engineering Chemical Engineering Department 2nd Stage EXP.NO.5
  2. 2. Introduction………………………………3 Aim of the experiment………………….4 Theory of the experiment……………...5 The description unit………………………6 The lay out unit …………………………….7 Apparatus ……………………………………8&9 Performing the experiment …………10 Discussion……………………………………11
  3. 3. The deadweight piston gauge (Bell and Howell) is used is to measure pressure in terms of fundamental units - force and area. A piston is inserted into a close fitting cylinder. Weights are placed on one end of the piston and are supported by fluid pressure applied to the other end. For absolute pressure measurements the assembly is placed inside an evacuated bell jar. Pressure measurements take into account a number of parameters affecting the instrument and its environment. they include the uncertainty of the mass of the weights and the error in the effective area measurement of the cylinder, gravity measurement, air bouyancy and temperature. Measurement units used are Kilopascals (Kpa) or Millibars (Mb). The available range is 20 Kpa. to 300Kpa. The accuracy we feel we have is better than 0.1mb. throughout the full range.
  4. 4. Calibrating the bourdon gauge.
  5. 5. Dead weight testers are named so because they utilize dead weights in determination of pressures operating in a closed and compressed fluid system. They are so called because of the reason that for each value of pressure to be exerted/ applied in the closed hydraulic system, a predetermined / fixed amount of weights are used to exert the force to counter balance the buoyancy forces. Each weight is stamped with the equivalent amount of force that will be exerted on a predetermined area of piston cylinder arrangement by using that weight. There fore the device is called Dead Weight tester. Working Principle: DWT (Dead Weight Tester) works based on the principle of Pascal's law. The law states that in a closed system of incompressible fluid, the pressure appliedwill exert equal amount of force in all the directions. In DWT system, silicon oil is used within the closed boundaries of the Piston cylinder arrangement, piping, pressurisation chamber and in the head on which the gauge to be tested/ calibrated is fixed. The oil is taken in to the pressurisation chamber from oil bowl and all the air entrapped is vented off. This is because of the reason that air iscompressible and hence do not allow pressure to be exerted equally in all the areas and there by create error in the test results. Once the system is full with air free oil, pressure is gradually increased from the pressurization chamber. Oil pressure starts increasing in all the areas including piston cylinder arrangement over which the dead weights are mounted. As the force increases gradually and equals the amount of down ward force being exerted by the dead weights, the total system gains the state of equilibrium and just at that moment, the dead weights starts getting lifted up. At this condition, the amount of force operating in the entire system is same. The sum of pressure values stamped on weights lifted is operating on the pressure gauge element also, which is under test/ to be calibrated. Necessary corrections are made in the zero/ span adjustments in gauges/ Pressure transmitters. Above sequence is repeated for all the values at 0%, 25%,50%,75% and 100% to check for linearity and repeatability. This is how the DWTs are working.
  6. 6. The device for calibrating pressure gauges essentially consists of two units: 1.the pressure gauge unit This is where the pressure gauge to be calibrated is screwed in. for experimental purposes ,the unit comes supplied with a bourdon gauge already screwed in. 2.the load unit The load unit consists of several weights and a cylinder with a piston. An increase in the load results in an increase in pressure . the load unit is connected to the pressure gauge unit via an oil-filled line , enabling the bourdon gauge to display the increase in pressure.
  7. 7. The following sectional drawing shows how the load unit and pressure gauge unit are connected. As you can see, both unit are means of a pipeline. When the support is loaded with weights, the oil pressure in the system increases . the seal between the piston and the cylinder is metallic, with on other sealing elements. The fit has been very carefully almost entirely without friction, and with minimal oil leakage. The weights are designed in such a way that pressure increments of 0.5 bar are possible. Place the small weight on the weight support first.A guide pin is provided for the purpose, the other weight would lie askew on the plunger, and would corrupt the measurements due to different levels of friction. The unit is also equipped with a drain valve in order to drain the oil. In addition, an overflow is incorporated, so that any leaked oil can be siphoned off .the overflow can be emptied via a tap.
  8. 8. Open the overflow valve _Remove the transport-cap _If necessary topping up the hydraulic oil _Inserting the piston _To check the zero point of bourdon gauge, proceed as follows: *press the piston out of the cylinder using the hand wheel. *Remove the piston and weight support. *adjust the oil level the open cylinder until the cylinder filled up the edge. The gauge pressure being tested should now indicate zero, as it is only subject to ambient pressure. _After the zero point of bourdon gauge has been checked, the weight support is re-inserted into the cylinder of the pressure gauge unit .the piston is then slowly lowered by unscrewing the counterbalance cylinder until it is freely suspended. _In order to avoid static friction . set the weight support in gentle rotation. the mass of the support is 385 g .taking into account the piston diameter of 12 mm, it is now possible to read the increase in pressure from bourdon gauge . _Other pressures occurring when the weight on the support is increased can be calculated in exactly the same way .the display of 0.5 bar is achieved by placing a weight with a mass of 193 g on the support .the other weights weigh 578 g, which is equivalent to a pressure increase of 0.5 bar each time.
  9. 9. The calibration curve appears because of equality in the ratio of Pacual &Pm ,it is a linear graph with equation of Y=1.0114x-0.11143 So the slope is 1.0114 with the rule of Y=mx+b For measuring (dead weight piston gauge) we use many types of bourdon gauge like
  10. 10. 1.C-type 2.Spiral
  11. 11. 3.Twisted 4.Helical
  12. 12. 1. 2. 3. 4. 5. d=77068 taggedpage/detaildisplay.cfm&contentid=25562