Inclined manometers allow for a finer resolution (measuring low values), usually in the hundredths (0.01) of an inch water gauge (in.wg.). It is important to make sure the inclined manometer is filled with the correct manometer fluid as some use water while others use an oil with a certain specific gravity. Always read the label on the inclined manometer. Also, before the inclined manometer may be used, it must be leveled and zeroed. Make sure the pressure fittings on the manometer are unscrewed enough to allow the pressure to get to the fluid. Test each side of the manometer by placing the pressure tubing in your mouth and blowing slightly; the fluid should move in response.
Though inclined manometers allow for greater precision than U-tube manometers, they are inconvenient to use when equipment is transported frequently. Therefore, U-tube manometers are usually used in these cases. Similar to inclined manometers, make sure the correct manometer fluid is used. Before the U-tube manometer is used, it must be zeroed. This is done by adjusting the scale so that the fluid levels are even at the 0-0 mark. Make sure the pressure fittings on the manometer are unscrewed enough to allow the pressure to get to the fluid. Test each side of the manometer by placing the pressure tubing in your mouth and blowing slightly; the fluid should move in response.
One potential drawback of the U-tube manometer is that it can be confusing. That is, you must remember that the pressure reading of a U-tube manometer is the difference in liquid column heights. For a U-tube that was zeroed, that means the pressure is double the reading on one side. For example, a pressure of 4 in.wg. will show as “2 inches up” on one side, and “2 inches down” on the other side.
Digital Handheld Manometers
Digital manometers typically range in price from $150 to $1000. More money buys greater resolution, accuracy and more features. Digital manometers are probably the most simple to use pressure measuring device. Some digital manometers have a resolution of 0.0005 in.wg. A potential drawback of digital manometers is that some can be susceptible to “drift”, which is when the pressure reading slowly strays. You should always zero the device before use.