The 8 Best Manometers
Handling The Pressure
A routine annual physical will often involve taking a patient's blood pressure. Air pressure within an inflatable rubber cuff is gradually increased and then decreased around the patient's arm, while an accompanying measuring unit allows the doctor to determine both systolic and diastolic blood pressure readings based on the change in height seen in a column of mercury. Also known as a sphygmomanometer, this device is a relevant segue into a discussion of the manometer in a more general sense. So whether you're a laboratory technician, a doctor, an HVAC technician, or a construction worker, assessing and understanding the pressure of various gases and liquids will be an important skill to have.
A manometer is an instrument designed to measure the differential pressure of a fluid or gas when compared to an outside source, such as the surrounding atmosphere. The device works on the principle of hydrostatic balance, which is a fancy way of describing the pressure exerted by a fluid or gas that is at rest. To imagine how this principle works, consider the common U-tube manometer. It consists of a curved glass tube partially filled with a column of liquid (e.g. mercury) and two graduated "legs". For clarity, let's call these the left and right tube legs. When the tops of these legs are exposed to the same volume of external pressure, the height of the liquid column within each one stays the same. When a force of outside pressure is pumped into the left leg, the liquid is forced downward, decreasing liquid height in the left while simultaneously increasing liquid height in the right leg. This process continues until the weight of the liquid balances the pressure. Once this balance is achieved, the observed difference in height of liquid between both tube legs will represent the amount of applied pressure that has just been introduced.
Manometers are classified into simple, differential, and digital types. Simple manometers measure pressure within a single container by comparing that pressure to normal atmospheric pressure. The U-tube manometer described above is one such example. Others include the piezometer, useful for taking groundwater measurements and studying seepage control systems; the well-type manometer, designed to measure very low pressures; and the inclined-tube manometer, engineered to measure small amounts of pressure using an angled leg for improved accuracy.
Differential manometers include both the U-tube and inverted U-tube devices, both of which may be used to measure the pressure difference between two points within the same pipe or between two completely separate pipes. For example, a differential manometer's ability to measure the flow dynamics of a gas by comparing pressure volume at different points within a single pipe makes it ideal for use in diagnosing problems with home HVAC systems.
Instead of using a column of liquid, the digital manometer leverages an internal microprocessor and pressure transducer to sense slight pressure changes, which are displayed on an electronic screen. Setting the digital manometer apart from its more traditional analog counterparts is its portability, allowing a user to take readings from anywhere without the dependence on a level surface for accuracy. Digital manometers can also record their own data and interface easily with computers, hence their popularity on our list.
Gauging The Right Choice
Manometers offer a wide range of applications. They can be used for atmospheric surveys, weather studies, gas analyses, medical procedures, and diagnosing problems with propane gas grills or heating systems. Before investing in one of these devices, it's important to identify what its intended purposes will be. Do you plan to use a manometer at home to monitor appliances or are you going to take it with you to the classroom? If you plan to use it on the go, a digital manometer will be a great choice due to its portability, ease of use, and ability to record data in almost any location. Many digital manometers are also equipped with convenient backlighting, which comes in handy if you're an HVAC professional working in dark spaces and trying to diagnose problems.
Another important consideration is whether you plan to measure a fluid or gas with your manometer. If it's the former, ask yourself whether the fluid you plan to measure is miscible with the measuring liquid or not. Is the measured fluid going to be heavier than the manometric fluid?
Think about the respective heights and distances between the two points you plan to measure, as this will help to guide you to the right solution for your needs.
Finally, if you decide to go with a digital manometer, make sure you find one with a durable plastic casing for withstanding impacts on the job.
A Brief History Of Manometers
In 1828, French physicist Jean Léonard Marie Poiseuille invented the first U-tube mercury manometer (also called the hemodynamometer), which he used to measure the pressures in the arteries of both horses and dogs.
By 1849, French watchmaker and engineer Eugene Bourdon developed a revolutionary new device that enabled accurate measurements of higher pressures than the U-tube manometer was capable of achieving. This new Bourdon gauge made it possible for engineers of the time to develop machinery that could operate at much higher pressures, such as improved steam locomotives.
Samuel Siegfried Karl von Basch is credited with the invention of the first blood pressure meter in 1896.
Today's digital manometers are designed for portability and ease of use. They now have the ability to wirelessly connect to the internet, perform automated tests, and export large amounts of data for detailed analyses. Manometers empower professional technicians to offer their clients data-driven recommendations that can help diagnose airflow problems and even conserve energy in buildings.