A manometer is a piece of clear (glass or plastic) tubing filled with a liquid of known density, situated next to a scale for measuring distance by using the motion-balance principle.
Types: U-tube, well, inclined, micro-manometer, ring balance, multitube & interface, and float types.
Sizes: Standard lengths from 6 to 140 in. (150 mm to 3.5 m)
Materials of Construction: Pyrex, brass, steel, aluminum, stainless steel
U-tube manometer
It is a fluid-filled tube where an applied pressure causes the fluid height to shift proportionately. Therefore, pressure is often measured in units of liquid height (e.g., inches of water, inches of mercury) which is
In a manometer, liquid column height should always be interpreted at the centerline of the liquid column, regardless of the shape of the liquid’s meniscus. Though U-tube manometers are generally made from clear plastic, they are very inexpensive.
Well Manometer
Manometers using a “well” have the advantage of single-point reading. One need only compares the height of one liquid column, not the difference in height between two liquid columns, consisting of a single vertical tube and a relatively large reservoir (called the “well”) acting as the second column.
The change in height within the well is usually negligible, as the cross-sectional area of the liquid column in the well is so much greater than the transparent manometer tube. In cases where the difference is significant, the spacing between divisions on the manometer scale may be skewed to compensate.
Inclined Manometer
This is the more sensitive manometers by purposely inclining one or more of the tubes so that the liquid must travel a farther distance along the tube length to achieve the same vertical shift in height. It can amplify the liquid’s motion to make it easier to resolve small pressures, such that a greater motion of liquid is required to generate the same hydrostatic pressure (vertical liquid displacement) than in an upright manometer, making the inclined manometer more sensitive.
Micro Manometer
For more sensitivity, the design is consisting of a gas bubble trapped in a clear horizontal tube between two large vertical manometer chambers, called a micro manometer.
The vertical liquid columns shift as the pressure applied to the top of either vertical chamber. There is a huge difference in cross-sectional area between the vertical chambers and the horizontal tube, where the bubble trapped in the clear horizontal tube will move much farther than the vertical displacement of either liquid column.
Ring Balance Manometers
A ring formed by tubing in such a way that the vertical plane is pivoted at its central axis, and the differential pressure rotates this ring. A weight attached to the ring developing opposing torque and shows the pointer deflection as per that. It detects absolute or near atmospheric pressures depending on the reference pressure used.
Multitube and Interface Manometers
Multitube manometer has up to 50 tubes connected in a common bank with atmospheric reference and the same number of process pressures can be detected from the same reference well. For flexibility, some or all the tubes can be provided with separate wells.
To precisely read or measure accurately the height of the liquid column accuracy is largely a function of the operator’s ability. For this, different designs have been made that tend to amplify the reading using magnifying eyepieces, vernier scales, or other techniques.
Float Manometers
The high pressure areas or hazardous areas require remote readouts, for which, float manometers are used. Due to pressure difference, it changes the level of filling liquid, and the float moves as per changing level. Float movement connected to a lever rotating in a pressure seal bearing which is used to drive the indicators.
List of Prominent Manufacturers: ABB Inc., Dwyer Instruments Inc., MKS Instruments, Meriam, BD SENSORS, Trox GmbH, Yokogawa Corp of America
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