# What is Gauge pressure: Definition and 68 Discussions

Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure meters or pressure gauges or vacuum gauges. A manometer is a good example, as it uses the surface area and weight of a column of liquid to both measure and indicate pressure. Likewise the widely used Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.
A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (e.g.: −15 psig or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale.
Other methods of pressure measurement involve sensors that can transmit the pressure reading to a remote indicator or control system (telemetry).

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1. ### Finding Gauge Pressure in this Manometer

Hi everyone. I would like to ask how do you find the gauge pressure at point 4. I know the formula, which is: Pgage = Pabs - Patm But I don't know which one is the Pabs. This is my attempt: P4 = (600 kg/m^3 × 9.8 m/s^2 × 0.05 m) + Ptank This is all I can do. Please professors help me on...
2. ### Finding gauge pressure for gas inside light bulb as it heats up

For this 19(a), The answer is 0.137 atm. My working is ##P_{gauge} = P_f - P_i## ##P_{gauge} = \frac{nRT_f}{V_f} - \frac{nRT_i}{V_i}## ##P_{gauge} = \frac{nRT_f}{V} - \frac{nRT_i}{V}## since volume does not change ##P_{gauge} = \frac{nR}{V}(T_f - T_i)## However, I am not sure how to go from...
3. ### What does atmospheric pressure have to do with the gauge pressure?

In this video( ) it's explained what is gauge pressure. Can someone please explain to me what does atmospheric pressure acting on a tube(in video at 3:51) has to do with displacement of a tube? I understand that the atmospheric pressure acts on the tube, but in the open space that does not...
4. ### Calculating this gauge pressure reading

Hi everyone! How do I go about solving this problem? I tried working out the gauge pressure using this but I have a few unknowns which won't make this possible such as what is the length of x which I labelled in the figure Any help would be appreciated! Thanks
5. ### Pressures in a U Tube along a line - different liquids

Yes, pressure is same along the line for both the tubes since the liquids are in equlibrium. (I ignore the slightly longer air column in the left compared to the right). Is my answer correct?
6. ### Gauge pressure due to a floating body

My answer : Both pressures are equal, i.e. ##\boxed{P_A = P_B}##. Reason : (1) The block of wood displaces an amount (mass) of liquid equal to its weight (archimedes' principle for floating bodies, or law of floatation). Hence we can imagine removing the block in the second case and filling it...
7. ### Gauge pressure of water oozing out of a pipe

Assuming water to flow out of the pipe with the same speed as inside and the thickness of water column ##h_{ab} = h_{cd} = h##, my answer would be ##\mathbf{(P_b = P_c) > (P_a = P_d)}##. My reasoning is as follows : at positions ##a\; \text{and}\; d## the gauge pressure is 0 and the total...
8. ### Difference between Absolute and Gauge Pressure

Hello all I was wondering someone could help clear up my understanding about the difference between Absolute and Gauge Pressure. After some reading i have been told that the Absolute Pressure is pressure taken at 0 relative to a vacuum. I am trying to understand what this actually means...
9. ### Gauge pressure in Momentum conservation of fluids.

I want to ask why is it that we use gauge pressure instead of absolute pressure in CV analysis for momentum conservation of fluids. I did read that because P(atm) would be present everywhere so it won't have a net effect on the CV but it's highly non intuitive as I can't apply force balance on...
10. ### Bernoulli Equation and gauge pressure

Homework Statement What gauge pressure is required in the city mains for a stream from a fire hose connected to the city mains to reach a vertical building of height 15m? Homework Equations Bernoulli Equation The Attempt at a Solution I have tried this sum. My confusion is regarding choice of...
11. ### How do I calculate the gauge pressure?

Homework Statement An automobile tire is pumped up to a gauge pressure of ##2.0 \times 10^5 ## Pa when the temperature is 27◦ C. What is its gauge pressure after the car has been running on a hot day so that the tire temperature is 77◦ C? Assume that the volume remains fixed and take...
12. ### Bernoulli's Equation, Find gauge pressure at 2nd point

Homework Statement At a certain point in a pipeline, the velocity is 1 m/s and the gauge pressure is 3 x 105 N/m2. Find the gauge pressure at a second point in the line 20 m lower than the first if the cross-section at the second point is one half that at the first. The liquid in the pipe is...
13. ### Hydrostatics, find length of kerosene column in U tube

Homework Statement A glass tube is bent into a U shape. Water is poured into the tube until it sands 12 cm high on each side. Kerosene (density = 870 kg/m3) is added slowly to one side until water on the other side raises 5 cm. What is the length of kerosene column? Homework Equations (ρhg)1 =...
14. ### Pressure reported from a water line, gauge or absolute?

Homework Statement Homework EquationsThe Attempt at a Solution I thought the pressure in a water line is in gauge pressure, but the solution suggests that 1630 kPa is in absolute pressure, do we always assume absolute pressure unless otherwise specified?
15. ### Finding the gauge pressure at the bottom of a barrel

Homework Statement A barrel contains 0.130-m layer of oil floating on water that is 0.290 m deep. The density of the oil is 610 kg/m3 What is the gauge pressure at the bottom of the barrel? Homework Equations P [/B]= ρ(g)(h) The Attempt at a Solution I found the pressure of the oil which...
16. ### When is gauge pressure absolute pressure?

Homework Statement Hi Physics gurus, this question was in my Chem Eng exam, and I can't agree with my lecturer's answer. He makes a LOT of mistakes, so it's hard to know when he's being clever or reallllly dumb. The question I have issue with is: "Is the pressure a manometric or an absolute...
17. ### What is the issue with calculating the gauge pressure of object B?

Homework Statement objects A and b are submerged at a depth of 1m in a liquid with a specific gravity of 0.877. Given that the density of object B is one third that of Object A and that the gauge pressure of object A is 3atm, what is the gauge pressure of object B? assume atmospheric pressure...
18. ### Pressure in district heating network

Homework Statement Can somebody explain the figure attached? Homework Equations H=p/(rho*g)+(v^2/2g)+z The Attempt at a Solution Search on the internet and looking in fluid mechanics book. Not possible to get book to get a explanation.
19. ### Gauge pressure at the bottom of a barrel

Homework Statement A barrel contains a 0.110 m layer of oil and a density of 690 kg/m3 floating on water that is 0.300 m deep. What is the pressure at the bottom of the barrel? Homework EquationsThe Attempt at a Solution Poil + Pwater = Ptotal My question is why am I using this formula? I...
20. ### What is the Maximum Constriction Radius in the Artery Given These Conditions?

Homework Statement A person has a 5200 N/m^2 gauge pressure in a 0.01m radius artery, with blood flowing at 0.5 m/s. the gauge pressure outside the artery is 3200 N/m^2. When using her stethoscope, a physician hears a fluttering sound farther along the artery. the sound is a sign that the...
21. ### Is absolute pressure same as gauge pressure?

From what I have read: Gauge Pressure: The amount by which the pressure measured in a fluid exceeds that of the atmosphere. and Absolute pressure: Total pressure at a point in a fluid equaling the sum of the gauge and the atmospheric pressures.So Absolute pressure= Patm+ P-Patm= P (Which is...
22. ### Gauge pressure and atmospheric pressure

Homework Statement Objects A and B are submerged at depth of 1m in a liquid with specific gravity of 0.877. Given that density of object B is one third that of object A and that the gauge pressure of object A is 3atm, what is the gauge pressure of object B? (assume atmos pres is 1 atm and that...
23. ### Change in gauge pressure using viscous flow through a pipe.

Homework Statement Water flows at 0.25 L/s through a 9.0-m-long garden hose 2.0 cm in diameter that is lying flat on the ground. The temperature of the water is 20 ∘C. What is the gauge pressure of the water where it enters the hose? Side question: does the velocity of the water flow need to...
24. ### When to use absolute or gauge pressure in computations

Hi! One of our professors told us once that in solving problems, always use absolute pressure in the computations. Then one time, I was solving some problems from Dr. Felder's Principles of Chemical Processes book, I often noticed that the pressures used in computations were not always in...
25. ### Calculating the Depth for 1 atm Gauge Pressure in Fresh Water

Homework Statement Approximately how deep into water must a diver dive to reach the point where the gauge pressure is 1 atm. (1 atm = 1.013 x 10^5 N/m^2) (assume fresh water) Homework Equations gauge pressure = pgd density of fresh water p = 1 kg/m^3 The Attempt at a Solution pgd = (1...
26. ### Why does a helicopter lift off the ground?

Agreed. The misunderstanding comes from the ambiguity of the word "pushing". I interpreted it as "applying a force", so a helicopter is pushing the air that it accelerates. [mod note: split from here: https://www.physicsforums.com/showthread.php?t=762789 ]
27. ### Bernoulli's equation, static fluid, gauge pressure problem.

Hi, I haven't done many problems of this nature so there are a few steps in my working that i'd like to check are acceptable/agree with what the question implies. Homework Statement A water tower is a familiar sight in many towns. The purpose of such a tower is to provide storage...
28. ### Solving a Water Pressure Problem: Gauge Pressure at B

Hi, I am working on this water pressure problem, given: v_A = 2.0 \frac{m}{s} gauge pressure_A = 50 kPa the view is from above, no height changes find: gauge pressure @ B so, A_Av_A=2(A_Bv_B) 1.5*10^{-2}m^2(2.0\frac{m}{s})=2(5*10^{-3}m^2v_B) v_B=9.0\frac{m}{s} Bernoulli's equation (w/o...
29. ### Bernoulli, Gauge pressure in hose?

Homework Statement A village maintains a large tank with an open top, containing water for emergencies. The water can drain from the tank through a hose of diameter 6.60cm. the hose ends with a nozzle of diameter 2.20 cm. A rubber stopper is inserted into the nozzle. the water level in the...
30. ### Calculating gauge pressure in lungs to produce certain speeds

Homework Statement The human sneeze can reach speeds of 150km/hr. Calculate the gauge pressure in the lungs required to generate a flow with this speed at atmospheric pressure. Assume the density of the air is constant at 1.3 kg/m^3. Homework Equations The Attempt at a Solution I...
31. ### How Does Absolute Pressure Differ from Gauge Pressure?

The formula for absolute pressure is absolute P=gauge P+atmospheric pressure. So when the gauge is at 0 it's actually 1 atm. So using the gas law if I were to half the volume the pressure would increase to 2 atm. So would the gauge read 1 atm when this happens? So how does the mechanism...
32. ### Fluids: potential flow, calculating gauge pressure from two sources

Homework Statement In a plane onset flow of 4 m/s, a source of strength 13 m2/s per metre is located at the origin (x=0, y=0) and another source of strength 18 m2/s per metre is located at (x=3m, y=0). Calculate the gauge pressure at the point (0, 2m), Take ρ =1.2kg/m3 Homework...
33. ### Trying to measure gauge pressure in a water pipe (under 1 psi)

I'm trying to measure and regulate gauge pressure in a pipe that has water flowing through it, but I need the pressure to be about .75psi (1.8 ft H2O). Most dial gauge ranges are too high and not accurate enough. Pressure transducers I've had no luck with as far as finding one that's inexpensive...
34. ### Solving Gauge Pressure with Boyle's and Charle's Law

good day! i was asked to solve for gauge pressure, pg1, using the combined Boyle's and Charle's Law, (pg1V1)T1=(pg2V2)T2 where V is the volume of gas and T is the temperature (in °C). now here's my question, we know that in computing for absolute pressure we need to convert the...
35. ### Calculating water pressure, gauge pressure

Homework Statement I've attached an image of a dam. The problem reads as follows: The fresh water behind a reservoir dam has depth D = 15 m. A horizontal pipe 4 cm in diameter passes through the dam at depth d = 6 m. A plug secures the pipe opening. Find the magnitude of the frictional force...
36. ### Gauge Pressure at the Bottom of Ocean on Mars

Homework Statement Scientists have found evidence that Mars may once have had an ocean .5km deep. The acceleration due to gravity on Mars is 3.71m/s^2. (a) What would be the gauge pressure at the bottom of such an ocean, assuming it was freshwater? (b) To what depth would you need to go...
37. ### 10 moles of an ideal gas has a gauge pressure of 2 atm what is new T? no clue

10 moles of an ideal gas has a gauge pressure of 2 atm what is new T?? no clue [b]1. Homework Statement [/b 10 moles of an ideal gas has a gauge pressure of 2 atm and a temperature of 200 K. If the volume of the gas is doubled and the pressure dropped to 1 atm., what is the new temperature...
38. ### MCAT contradiction? - Gauge Pressure

Homework Statement A large cylinder is filled with an equal volume of two immiscible fluids. A balloon is submerged in the first fluid; the gauge pressure in the balloon at the deepest point in the first fluid is found to be 3 atm. Next, the balloon is lowered all the way to the bottom of the...
39. ### How do I find the gauge pressure?

A rectangular fish tank measuring .75 x .50 m is filled with water to a height of 65 cm. What is the gauge pressure on the bottom of the tank? So I'm pretty sure I use the equation P=densityxgravityxheight I know gravity is 9.8, but I'm not sure what height I should use considering it is...
40. ### Thermodynamics- Gauge pressure, moles, molecules

Homework Statement A 4.0 m^3 container of oxygen gas has a gauge pressure of 8x10^5 Pa at 25 degrees c. a) how many moles of oxy are present in the containe?r ANS: 1292 moles b)how many oxy molecules are present? ANS: 7.78E26 oxy (yes, i have the answers but i don't know how to get to them...
41. ### Gauge Pressure of Tires - find car mass

Gauge Pressure of Tires -- find car mass Homework Statement The gauge pressure in each of the four tires of an automobile is 240 kPa. If each tire has a "footprint" of 22.0 cm-squared, estimate mass of the car. P=240 kPa A=22.0 cm-squared g=9.8 m/s^2 Homework Equations P=F/A 1 atm =...
42. ### Gauge pressure at the base & top of the dam?

Homework Statement This is a two part problem: a) A reservoir behind a dam is 56 m deep. What is the gauge pressure at the base of the dam? The acceleration of gravity is 9.8 m/s 2 and atmospheric pressure is 10100 Pa . Answer in units of kPa. b) What is the gauge pressure 19 m from...
43. ### Calculating Gauge Pressure at the Bottom of a Test Tube

Homework Statement A test tube standing vertically in a test tube rack contains 3.8 cm of oil, whose density is 0.81 g/cm3 and 6.4 cm of water. What is the gauge pressure on the bottom of the tube? The acceleration of gravity is 9.8 m/s2. Answer in units of Pa Homework Equations...
44. ### Gauge Pressure at 10m in a Muddy Lake

Homework Statement The Variation of the density with depth h in a muddy lake is given by ρ=ρ0+kh, where ρ0= 1000kg/m^3 is the density at the surface and k=100kg/m^4 Calculate the gauge pressure at a depth of 10m.
45. ### What is the Formula for Calculating Gauge Pressure of Tires?

Homework Statement The weight of a 1142-kg car is supported equally by the four tires, which are inflated to the same gauge pressure. What gauge pressure is required so the area of contact of each tire with the road is 96.5 cm^2? W = 1142 kg A = 96.5 cm^2 Homework Equations No idea...
46. ### Calculating the gauge pressure?

Homework Statement Water flows through a .259m radius pipe at the rate of .125m^3/s. The pressure in the pipe is atmospheric. The pipe slants downhill and feeds into a second pipe with a radius of .190m, positioned .796m lower. What is the gauge pressure in the lower pipe? The acceleration of...
47. ### Gauge Pressure problem (algebra based)

Homework Statement What is the gauge pressure at a depth of 100 m. in water?Homework Equations Pgauge = rho*g*h (or the pressure above atmospheric pressure)The Attempt at a Solution I missed a day of class (and on a summer class, that's a LOT of material). I am working problems that are...
48. ### Calculating Gauge Pressure in a Two-Story House

The main water line enters a house on the first floor. The line has a gauge pressure of 2.00 x10^5 Pa. (a) A faucet on the second floor, 7.0 m above the first floor, is turned off. What is the gauge pressure at this faucet? P2= P1 + (density x g x h) (2 x 10^5)= P1 + (1000 x...
49. ### Giraffe Blood Pressure: Calculating Gauge Pressure at the Brain

In a giraffe with its head 2m above its heart , and its heart 2m above its feet, the hydrostatic gauge pressure in the blood at its heart is 250 torr . Assume that the giraffe stands upright and the blood density is 1.06 * 1000kg/cubic metre.In torr find the (gauge) blood pressure at the brain.
50. ### Finding gauge pressure when the faucet is turned off

Homework Statement The main water line enters a house on the first floor. The line has a gauge pressure of 1.70 X 10^5 Pa. (a) A faucet on the second floor, 5.2 m above the first floor, is turned off. What is the gauge pressure at this faucet? Pa (b) How high above the water main could...