Reading Static Pressure with a Manometer¶
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About This MicroSim¶
A U-tube manometer has one leg connected to the duct and one leg open to the room. The difference between the two water levels, in inches, is the static pressure in inches of water gauge (in. wg). When the duct is above room pressure, the water is pushed down on the duct leg. When the duct is below room pressure (suction), the room pushes the water up the duct leg.
The sim draws the supply system from the chapter's worked example "Adding Up a System's Resistance": intake louver, filter, coil, fan, ductwork, diffuser and room, with each part's pressure drop. You step through six measurement points in order. At each one the manometer's water levels are hidden behind a shutter. You choose a sign and type the size of the reading, then press Check. The shutter opens to show both water levels on a ruler, and the reading is labeled on the system drawing, so the pressure profile builds up across the system.
| # | Point | Correct reading (in. wg) | Water on the duct leg |
|---|---|---|---|
| 1 | After the intake louver | −0.15 | Up |
| 2 | After the filter | −0.65 | Up |
| 3 | Fan inlet, after the coil | −1.40 | Up |
| 4 | Fan outlet | +1.10 | Down |
| 5 | Before the diffuser | +0.15 | Down |
| 6 | In the room | 0.00 | Level |
Question 7 asks how much static pressure the fan must add. The answer is 2.50 in. wg: outlet minus inlet, \( 1.10 - (-1.40) \). This treats the air velocity at the fan inlet and outlet as equal, as the chapter states.
A reading is correct when the sign matches and the size is within ±0.05 in. wg. A reading of 0 for point 6 is correct with or without a sign. Each item has one scored attempt. A correct answer shows "✓ Correct:
After question 7 the sim switches to Review mode, which is never scored. Pick any point to see its manometer, its reading and the reason again. The summary shows the first-attempt score, the mastery line and a ✓ or ✗ for each item. Start over runs all seven again.
How to Use¶
- Read the question and the pressure drops under the drawing. Decide whether the duct at the marked point is above or below room pressure.
- Choose + above room or − below room, type the size of the reading in the Reading box, and press Check (or Enter). You can also type the sign in the box, for example
-0.15. - Compare the water levels with your answer. If you missed, you may enter the reading again and press Retry (not scored).
- Press Next point to move on. After point 6, answer question 7 with the fan's static pressure rise.
- In Review mode, choose a point from the Review menu (or press 1 to 7, or click a numbered point) to see its manometer again. Press Start over to repeat the seven items.
Keyboard: Tab reaches every control; the arrow keys change the sign; Enter checks the answer, and after an answer Enter goes to the next point. In Review mode, keys 1 to 7 choose a point.
Data label: "Illustrative values from the chapter worked example", shown at the bottom left of the drawing.
Iframe Embed Code¶
You can add this MicroSim to any web page by adding this to your HTML:
<iframe src="https://moroshek.github.io/FanTASTIC-textbook/sims/ch01-manometer-static-pressure/main.html"
height="662px"
width="100%"
scrolling="no"></iframe>
Lesson Plan¶
Learning Objective¶
The learner will interpret U-tube manometer readings taken at six points in a supply system as signed static pressures in inches of water gauge, and infer the fan's static pressure rise, with at least 6 of 7 answers correct (Bloom: Understand, verb: interpret).
Audience¶
Adult professional development: new application engineers, sales staff, representatives and facilities staff.
Duration¶
10-15 minutes
Prerequisites¶
- Air pressure, atmospheric pressure, gauge pressure and suction
- Inches of water gauge and the manometer
- Static pressure and pressure drop
All are covered in the Chapter 1 sections "Air Pressure", "Inches of Water Gauge" and "Static Pressure".
Activities¶
- Readings (6 min): Work points 1 to 6 in order. Commit to a sign and a size before each check, and watch which leg the water moves on.
- Fan rise (2 min): Use the inlet and outlet readings on the drawing to answer question 7.
- Review (3 min): Open point 3 and point 4 side by side in your mind: the same fan, the water pulled up on one side of it and pushed down on the other.
- Discussion (2 min): Why is a reading at the fan inlet negative even though the fan is "making pressure"?
Common Misconceptions Addressed¶
- Static pressure is always positive: points 1 to 3 are negative, and the sim names a right-size, wrong-sign answer.
- The water rises on the duct leg when the duct is pressurized: the revealed manometer shows the water pushed down on the duct leg at points 4 and 5, and the caption says which way it moved.
- The fan's pressure rise is the outlet reading alone: question 7 recognizes 1.10 and explains that the inlet suction counts too.
Assessment¶
- First-attempt score shown as "First-attempt correct: n of 7"; mastery is 6 of 7 on the first attempt. The summary shows "Mastery reached (6 of 7 needed)." or what is still needed.
- The unscored retry and Review mode are not evidence of mastery. Follow up: a filter loads up and its drop doubles. Which readings change, and does the fan's required rise change?
References¶
- Chapter 1: Air, Pressure and the Fan - The "Static Pressure" section and its worked example "Adding Up a System's Resistance".
- FanPedia online, Twin City Fan - The fan and blower encyclopedia this textbook is built from.
- Pressure measurement: manometers, Wikipedia - How a liquid column measures a pressure difference.
- Inch of water, Wikipedia - The unit used for fan and duct pressures.