Manometers and Magnehelic Gauges

row of industrial manometers

Cleanrooms provide a controlled environment. Pressure, temperature, and humidity are the most critical factors to control to prevent contamination. Different industries have different requirements when it comes to controlling parameters.

Although, all parameters are critical, but the pressure is most critical in cleanroom application to maintain GMP classifications for the product being manufactured in the cleanroom.  

There are three types of pressure measurement: positive, negative, and differential. Positive pressure is the one that is greater than atmospheric pressure. Negative pressure is less than atmospheric. Differential pressure is the difference between positive and negative pressures.

There is a need for pressure measurement equipment to make sure the pressure is always at the levels necessary. Several tools could be used for pressure measurement. Manometer and magnehelic gauges are two frequently used tool which are discussed below.


Working Principle and operation

Manometers have different applications, including determining static pressure, velocity, leakage, filter resistance, and gas pressure. Most commonly, manometers are used to measure liquid and gas pressure.  

Manometer consists U shape glass tube which is filled with mercury or some other liquid. Traditionally one end of the manometer tube is left open, susceptible to atmospheric pressure, while a manometer hose is connected via a gas tight seal to an additional pressure source. While normally associated with gas pressures a manometer gauge can also be used to measure the pressure exerted by liquids.

Initially end of tube is open so that pressure exerted on both sides will be same.  If one end of the U-tube is left open to the atmosphere and the other connected to an additional gas/liquid supply this will create different pressures.

If the pressure from the additional gas/liquid supply is greater than the atmospheric pressure this will exert a downward pressure on the measuring liquid. Therefore, the liquid will be pushed down on one side with the greater pressure causing the liquid to rise on the side with the lesser pressure. The opposite would occur if the additional gas/liquid supply creates a lesser pressure than the atmospheric pressure. Usually, there is number indicated on the U tube, from which displacement of liquid inside the tube can be evaluated and that will accurately provide pressure.

Types of Manometers

analog manometer

Analog type manometer

Analog manometers use the U-shaped tube with fluid to test the pressure. When using analog manometers, it come with a dial, it moves and get a “feel for reading.”

If there is no pressure, the fluid will stay in the middle of the tube. The fluid moves when the pressure is higher on one side of the tube.

Analog manometers also measure the differential pressure by stabilizing the weight of a liquid between two pressures.

A significant reason technician sometimes prefer analog manometers is that they don’t require a power supply. This way, you can ensure it won’t unexpectedly run out of power.  Picture of analog manometer is shown below.

digital manometer

Digital Manometer

Digital manometers use a sensor or transducer to determine pressure instead of fluid. Sensors and transducers transform observed pressure levels into an electric signal. Technicians then use the signal to understand the pressure.

Unlike the analog version, digital manometers are more portable and easier to carry. It is also easier to read the result. There is an easy-to-read display on a digital manometer while you must squint to line up a needle against the numbers to undergo the data on the analog version. The simplicity in readings also helps to prevent mistakes.

Another benefit of a digital manometer is that the data collected could be recorded and transmitted to computers via Bluetooth or special cables. 

magnehelic guage

Magnehelic Gauge

Magnehelic gauge is another tool that can be used for measuring pressure. Like a manometer, it can also measure static pressure, differential pressure, and air velocity. Unlike the manometers, it uses an entirely different process to determine pressure. Magnehelic gauge incorporates the Magnehelic principle developed by Dwyer. When gauge is placed to measure pressure diaphragm vibrates and move the helix which is connected with needle magnetically (no physical contact). Needle is linked to pointer with linkage and that will show pressure difference on gauge.  The diaphragm is very sensitive and perceives the differential in air pressure exerted on it. The design of the gauge is resistant to shock, vibrations, and over-pressures.

Magnehelic gauge is better than other gauges because it eliminates problems like backlash, excessive wear, and toxicity. In addition, it is considered to be one of the most accurate tools to measure pressure with an accuracy of just plus or minus 2% at full scale. Magnehelic gases are designed to measure the pressure within a precise range. Some gauges might have a range of -3000 to +8000 pascals. 

Magnehelic gauges are usually used for cleanroom HVAC applications. The indicator works without discrepancies in very cold or very hot weather. It is effortless to install, and unlike manometers, it does not need to be in a specific position or be perfectly leveled.

magnehelic guage
Display of Gauge with tube connection in rear side

No matter the location, the gauge must be zeroed as a final step to be used in the position installed. If zeroing is done before the installation, the reading must be wrong as they will vary more than 2%. You can move the gauge from place to place, but it has to be zeroed every time it is relocated. 

rear side of magnehelic guage
Rear side of gauge with high- and low-pressure port

To choose the best manometer or magnehelic gauge for you, make sure to understand which measurements you’ll be reading most. Get in touch with our team to learn more and choose the perfect fit for your needs.