VACUUM PRESSURE MEASUREMENT Laboratory Procedure Background InformationPressure is defined...

VACUUM PRESSURE MEASUREMENT Laboratory Procedure Background Information

Pressure is defined as a force per unit area. A common unit of pressure is pounds per square inch or simply psi. At sea level, atmospheric pressure averages 14.7 psi on the absolute pressure scale and zero (0) psi on the gauge pressure scale. Atmospheric pressure is dynamic, meaning that it changes according to weather conditions. If a vessel is blocked in, the internal pressure drops below atmosphere and the pressure across its walls exceeds its rated capacity, then extensive damage to the vessel can occur in the form of crushing. Most vessels are not designed to withstand significant pressure applied from the outside inward.

Consider the following example. A storage tank is prepared for maintenance by removing all process materials from the vessel and then steaming out the vessel. All connections on the tank are closed. Then, cold wet rain drenches the tank for several hours during the evening time causing the steam in the tank to condense. When the day shift process technicians make their first rounds on the following morning, they find the tank has been crushed on one side causing extensive damage.

Materials Needed

• vacuum source

• copper tubing

• vacuum gauge or a psig gauge that reads negative pressure or a psia gauge

• a vessel to vacuum source connecting apparatus

NOTE: The materials needed for this apparatus can be found at most hardware stores.

• a gallon tin can or plastic liter bottle

Safety Requirements

Safety glasses are required in the lab due to the potential dangers associated with imploding or exploding vessels.

Procedure

a. Connect the container to be tested to a vacuum source. If the vacuum source does not have a pressure indicator mounted to it, then you will have lo connect one to the apparatus with a tubing tee.

b. Make sure the gauge is indicating zero before starting the experiment.

c. Slowly apply vacuum lo the plastic container.

d. Record the reading at the initial wall collapse and then again when it is completely collapsed.

e. Apply the same amount of positive pressure to the plastic bottle.

Safety Tip: There is a danger of explosion.

f. Record your observations.

g. Do this to several containers if time allows.

h. Complete the final report for this lab.

Findings

Compile your observations and readings into a report that includes your recorded data, an explanation of the results of the experiment, and a conclusion. Include a paragraph explaining how a process technician could guard against the scenario provided in the background information.