Test 1

Question 1

Bubbler tube advantages

Answer 1

• Low cost
• Simplicity
• Adaptability for vessels of varying sizes/shapes

Question 2

Bubbler tube disadvantages

Answer 2

If liquid density changes, level indication can be affected

Question 3

Hydrostatic Head Pressure principle of op

Answer 3

• A bubble system is used to detect the hydrostatic pressure in a vessel and transmit it to another location, often using an inert gas to communicate the level information.
• The hydrostatic head created by a liquid is proportional to the height of the liquid above the pipe opening.
• The pressure required to equal the hydrostatic head measures the liquid level

Question 4

Leaks in a bubble tube system are indicated by….

Answer 4

Little or no back pressure/level indication but a normal flow rate on rotameter

Question 5

Plugs in a bubble tube system are indicated by…

Answer 5

Maximum back pressure, no flow

Question 6

3 ways to eliminate pressure drop error

Answer 6

• Run two lines to measuring element dead-ended
• Use larger diameter pipes or tube for bubble tube supply
• Reduce the flow rate to the minimum required

Question 7

What is the minimum height a bubble tube should be kept from the bottom of the tank? (if possible)

Answer 7

3”, in cases where sedimentation is possible

Question 8

Sight Glass Use

Answer 8

• Indication, not control
• Provides a direct and accurate reading
• Used with applications ranging from low pressure open tanks to very high pressure steam applications
• Purpose of a level gauge or sight glass is to let operator actually check the level in the tank from the outside

Question 9

Sight Glass Accessories

Answer 9

• Lights and/or coloured backgrounds -> provided to make it easier to read the level of clear liquids or improve the readability of sight glasses
• Check valves allow only fluid to flow through a level gauge in one direction. -> Used when there are large differences in pressure or to reduce spills if the glass becomes broken
• Shut off valves -> are used so sight glass can be removed or replaced without disturbing the process

Question 10

Conductivity units are…

Answer 10

Siemens/cm (s/cm)

Question 11

Conductivity Probe Op

Answer 11

• The fluid in the tank or vessel completes an electrical circuit between 2 probes or between 1 probe and the vessel
• A voltage is supplied to the probe when the fluid contacts the probe -> current will flow through the fluid to the other conductor
• Can be used on most liquids as the probes can be made from different materials

Question 12

Conductivity Probe Advantages

Answer 12

• Good for slurries, acids and high-pressure applications
• Simple
• Inexpensive

Question 13

Conductivity Probe Disadvantages

Answer 13

• Cannot be used with a liquid that will build up on the probe
• Solution has to be electrically conductive

Question 14

Capacitance Probe Op

Answer 14

• Utilizes a variable capacitance element as one leg in a bridge-type measuring circuit
• Can perform on-off as well as continuous measurements
• Should be used with clean liquids as build up on the surface may be a concern
• Routinely designed for up to 260 degrees C and 1000psi

Question 15

Conductive Solutions Capacitance Probe (Type 1) Op

Answer 15

• Consists of a probe separated from the conductive material being measured with an insulator
• This insulator is usually a teflon coating on the probe
• In this case the teflon coating acts as the dielectric and conductive being measured as the second plate -> As the level changes the size of the second plate changes -> producing an output proportional to the level

Question 16

Non-Conductive Solutions Capacitance Probe (Type 2) Op

Answer 16

• Two probes are used and liquid acts as the dialectric
• Second probe can be wall of tank if conductive
• These probes act as the capacitor plates
• Since the size of the plates and the distance between the plates are constant any change in output will be due to level in the tank

Question 17

Ball Type Float:

Answer 17

• For level indication or switch actuating in atmospheric tanks or stumps
• Rod motion is used to indicate level on gauge or trip combinations of high/low switches for alarms and/or automatic starting of pumps

Question 18

Top/Side Mounted Float Switch:

Answer 18

• Float position is transmitted to outside of vessel via a rigid arm through a seal
• Direct connection usually requires that the vessel be de-pressurized for maintenance unless an external chamber isolated from vessel by shut off valves is used

Question 19

Tape gauge operated by float and gauge board for level indication:

Answer 19

• Tape connected to float at one end and the counterweight at the other which keeps the tape under tension
• Float moves weight up and down in front of gauge board indicating level in tank
• Guide cables must be used if tank diameter is large so that the float stays in the center of the tank

Question 20

Torque Tube Displacers:

Answer 20

• Tube in torsion provides the function of the spring
• The hollow torsion tube supports the displacer which is always denser than the process fluid and provides a frictionless seal
• This makes it possible to transfer the changes in a parrot weight of the displacer through the wall of the pressure vessel into a measuring device

Question 21

Float Type Level Device Advantages:

Answer 21

• Inexpensive
• Can be easy to install
• Can protect pumps from damage or air locking

Question 22

Float Type Level Device Disadvantages:

Answer 22

• Can have scaling (E.g. minerals in water building up) and build-up
• Maintenance requires access to process
• Displacers: are dependent on the density of the process
• Displacer: can have limited ranges

Question 23

Still-well notes

Answer 23

• If there are disturbances in a tank or vessel, still-wells must be used
• There are two places to locate a still-well -> inside or outside of the tank

Question 24

Sight Glass Best Application:

Answer 24

Clean, clear liquids

Question 25

Level Transmitter Principle of op

Answer 25

- Connected at the bottom of a tank -> measures head pressure - Dependent on density - A diaphragm type can be used with suspended solids but it can scale up and may be difficult to remove - Scales for gauges can be obtained to read the actual level - Measured liquid must enter the gauge or transmitter - If corrosive liquids are measured stainless steel may be required

Question 26

Level transmitter advantage:

Answer 26

Simple and can be inexpensive

Question 27

Level transmitter disadvantages

Answer 27

- Used for open vessel application only - Used for liquid only applications

Question 28

Closed vessel containing internal pressure (dry leg) Notes:

Answer 28

- Dry internal pressure applied to both sides of gauge/transmitter -> internal pressure cancels out - Used to measure level in a closed vessel as this method eliminates errors due to changes in internal tank pressures - Both high and low sides of the d/p transmitter are connected to the tank - High leg to the bottom of the tank, low leg to the top

Question 29

Closed vessel containing internal pressure (wet leg) Notes:

Answer 29

A wet leg application would be used if condensation is a possibility (E.g. steam drums) Used often in high-pressure applications Dependent on liquid density