What is a Manometer?
A manometer is a device that measures air pressure by using a column of liquid in a vertical tube. It measures the pressure of a fluid relative to an external source, such as the Earth’s atmosphere.
It is a U-shaped tube filled with water that is used to measure pressure differences. Its arms move the fluid to different heights depending on the pressure difference. It can also be used when a manometer is not available in a particular area.
Difference between a barometer and a manometer
Manometer
A manometer is a device used to measure pressure, usually atmospheric pressure. Manometers have been used for centuries and have a variety of designs, from old-fashioned glass tubes filled with mercury or water to newer digital devices.
Barometer
Like a barometer, it measures atmospheric pressure. In fact, a barometer is a closed pressure-measuring device. However, a barometer has a more limited design and functionality than a thermometer. All barometers are manometers, but not all manometers are barometers.
Difference between a manometer and a barometer
Barometer
Manometers are a branch of manometers with a basic design: a closed tube. Specifically, a traditional barometer is a glass tube that is open at one end and evacuated at the other. At the open end, the atmosphere exerts pressure on the liquid inside the tube. This liquid, usually mercury, adjusts to the increased pressure exerted by the outside gas because the vacuum at the closed end of the tube does not change the height of the mercury.
Closed barometers can be either U-shaped or well-shaped. In a well manometer, a mercury tube is inverted or turned upside down into a larger mercury well so that the vacuum-sealed end is at its highest point and the open end is suspended in liquid. The outside gas exerts pressure on the mercury well, causing it to expand inside the closed tube.
Today, barometers can also be digital or aneroid, making them portable; traditional glass barometers should be placed on a table or in an upright position. Aneroid barometers (such as those in cars) may have numbers or a clock face. These barometers contain a series of gas-filled cells that rise in response to atmospheric pressure. This activates a lever connected to a battery, which changes the dial on the face of the barometer.
Manometer
Manometers can be open, closed, or digital. An open manometer contains a liquid, such as water or mercury, and the tube is U-shaped. Both ends of the U-shaped tube can be exposed so that the atmosphere exerts pressure on both sides. An open manometer does not need to have arms of the same size on the tube, and it can have a well at one end.
In addition to the simple open U-shaped gauge, many gauges have a bulb or other fitting filled with a high-pressure gas at one end. The gas exerts pressure on one end of the tube, while atmospheric gas exerts the same pressure on the other end. Thus, the manometer can measure different types of gas pressures.
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Another more accurate gauge is the inclined tube gauge. It is an open gauge, usually with a vertical slope of 2.5 cm and a well at the lower end. This slope allows for more accurate measurement of lower pressures.
In a closed gauge, one end is connected to a high-pressure gas, and the other end is connected to a vacuum, rather than being exposed to air. Barometers also have this feature, but they measure only atmospheric gases.
Internal Fluid
Barometer
Barometers are usually filled with mercury. A thick liquid is needed, or the barometer must be very high to display relatively large changes in air pressure. In a digital or aneroid barometer, there is no liquid; instead, there is a gas chamber.
Like a barometer, a glass manometer is usually filled with mercury or another high-density liquid. However, open gauges can also be filled with lighter liquids that may show smaller pressure changes. These liquids include water, oil, bromides, and gasoline. Using water or oil can help with mercury-related problems, such as poisoning and toxicity.
Pressure Calculations
Barometer
Reading a mercury barometer is relatively simple. Since only the open end affects the height of the mercury, the user simply reads the specified height of the closed end under vacuum. This should give the atmospheric pressure in millimeters or inches, which can be converted to torr. (For example, a typical atmospheric pressure at sea level displayed by a mercury barometer should be 760 mmHg, or millimeters of mercury.)
Manometer
The atmospheric pressure in an open manometer is read as the difference in height between the liquid in each arm of the tube. In an open barometer with atmospheric gas on both sides, the height difference is measured in millimeters or inches, which can be converted to hectopascals.
When a manometer is open on one end and connected to a high-pressure gas, consideration must be given to which arm contains more liquid. If the side open to the air contains more liquid, the high-pressure gas exerts a greater force, and the height above sea level must be added to the atmospheric pressure. If the opposite happens for the arms, the height above sea level must be subtracted from the atmospheric pressure. This will show the pressure exerted by the high-pressure gas.
If the manometer is closed on one end (creating a vacuum) and also connected to a high-pressure gas, then, like a barometer, the pressure is the height of the closed arm.
Barometer
The vacuum at the closed end of a barometer is particularly useful for measuring atmospheric pressure. This makes the mercury barometer a traditional tool in weather forecasting and meteorology, fields that rely on changes in air pressure to predict weather patterns.
Manometer
Other types of manometer can measure pressures below and above atmospheric pressure. By connecting a lamp or other high-pressure gas device to a manometer, the pressure of that gas can be calculated. However, in some cases, a barometer may be necessary to measure a reference atmospheric pressure.
Why and where is it needed on a ship?
This manometer can be used for various applications on board ships, such as:
Main engine air cooler:
The air cooler cools the hot compressed air coming from the turbocharger. In this way, the air temperature decreases and the density increases. A higher density means a greater mass of air delivered, which improves engine efficiency. The turbocharger supplies fresh air to the engine, which sometimes clogs the intercooler fins, resulting in reduced cooling efficiency and inadequate combustion of the main engine. To determine its condition, we use a manometer attached to the side of the radiator.
Main Engine Turbocharger Felt Filter:
A felt filter is an air filter used in turbocharger systems to protect the turbocharger from damage caused by debris and other airborne contaminants. Over time, these contaminants can build up on the filter surface, causing a pressure drop that can affect turbocharger performance.
By measuring the pressure drop across the felt filter using a manometer, you can determine when it needs to be replaced or cleaned. One point on the manometer is located outside the turbocharger, and the other point is located inside the turbocharger. When air is drawn in, a vacuum is created inside the gauge, so the pressure outside the gauge is raised by atmospheric pressure, allowing us to get the pressure differential.
How do we interpret the pressure gauge readings on our boat?
The gauge pressure on a turbocharger depends on one main factor:
Main Engine Load:
The main load of an engine refers to the power it produces, which is directly related to the amount of fuel it burns. Main engine load is affected by a number of factors, including ship speed, sea conditions, and power demand. When the main engine runs at a higher rpm, it burns more fuel and produces more exhaust gases. These exhaust gases drive the main engine’s turbocharger turbine to run at a higher speed, which increases the turbocharger speed. The increase in turbocharger speed causes the turbocharger to inhale more air and compress it further, increasing the pressure of the inhaled air.
As a result, more air passes through the air cooler, resulting in an increase in the pressure drop at the radiator. The increase in pressure drop causes an increase in the manometer reading. In addition, increasing the main engine speed increases the turbocharger blower speed, which creates more vacuum in the muffler area. This, in turn, increases the manometer reading. Conversely, when the main engine speed is significantly lower, the pressure drop on the air side of the air cooler is reduced. Therefore, the prime mover load and engine speed are interrelated, and increasing one will cause the other to increase as well.
