Dwyer Instruments - Primer On How Our Products Work. Introduction. In air conditioning, heating and ventilating work, it is helpful to understand. In this field, air. FPM). By multiplying air velocity by the cross section area. Volume flow is usually measured in cubic feet per minute. Velocity or volume measurements can often be used with engineering handbook or design information to reveal proper or improper performance of an airflow system. The same principles used to determine velocity are also valuable in working with pneumatic conveying, flue gas flow and process gas systems. View and Download Kia Sportage owner's manual online. Sportage Automobile pdf manual download. FREE SHIPPING — Powerhorse Inverter Generator — 3500 Surge Watts, 3000 Rated Watts, Electric Start, EPA and CARB Compliant, Model# LC3500i. Nord 2501 Noratlas: no more uneven cargo floors! www.reocities.com/CapeCanaveral/Hangar/2848/noratlas.htm. The Nord Noratlas was designed for the French Air Force as. However, in these fields the common units of velocity and volume are sometimes different from those used in air conditioning work. To move air, fans or blowers are usually used. They work by imparting motion and pressure to the air with either a screw propeller or paddle wheel action. When force or pressure from the fan blades causes the air to move, the moving air acquires a force or pressure component in its direction or motion due to its weight and inertia. Because of this, a flag or streamer will stand out in the air stream. This force is called velocity. It is measured in inches of water column (w. In operating duct systems, a second pressure is always present. It s independent of air velocity or movement. Known as static. pressure, it act equally in all directions. In air conditioning work, this pressure is also measured in inches w. In pressure or supply systems, static pressure will be positive on the discharge side of the fan. In exhaust systems, a negative static pressure will exit on the inlet side of the fan. When a fan is installed midway between the inlet and discharge of a duct system, it is normal to have a negative static pressure at the fan inlet and positive static pressure at its discharge. Total pressure is the combination of static and velocity pressures, and is expressed in the same units. It is an important and useful concept to us because it is easy to determine and, although velocity pressure is not easy to measure directly, it can be determined easily by subtracting static pressure from total pressure. This subtraction need not be done mathematically. It can be done automatically with the instrument hook- up. Sensing Static Pressure. For most industrial and scientific applications, the only air measurements needed are those of static pressure, total pressure and temperature. With these, air velocity and volume can be quickly calculated. To sense static pressure, five types of devices are commonly used. These are connected. Fig. 1- A shows a simple thru- wall. This is a sharp, burr free opening through a duct wall. The axis of. the tap or opening must be perpendicular to the direction of flow. This type. of tap or sensor is used where air flow is relatively slow, smooth and without. If turbulence exists, impingement, aspiration or unequaled distribution. Fig. 1- B shows the Dwyer No. A- 3. 08 Static Pressure Fitting. Designed for. simplified installation, it is easy to install, inexpensive, and provides accurate. FPM. Fig. 1- C shows a simple tube through the wall. Limitations of this type are similar to wall type 1- A. Fig. 1- D shows a static pressure tip which is ideal for applications such as. Here the probability of air turbulence requires that the pressure sensing. For a permanent installation of this type. A- 3. 01 or A- 3. Static Pressure Tip is used. It senses static pressure through. Fig. 1- E shows a Dwyer No. A- 3. 05 low resistance Static Pressure Tip. It is designed for use in dust- laden air and for rapid response applications. It is recommended where a very low actuation pressure is required for a pressure switch or indicating gage - or where response time is critical. Measuring Total Pressure and Velocity Pressure. In sensing static pressure we make every effort to eliminate the effect of air movement. To determine velocity pressure, it is necessary to determine these effects fully. This is usually done with an impact tube which faces directly. This type of sensor is frequently called a "total pressure pick- up" since. In Fig. 2, note that separate static connections (A) and total pressure connections (B) can be connected simultaneously across a manometer (C). Since the static pressure is applied to both sides of the manometer, its effect is canceled out and the manometer indicates only the velocity pressure. To translate velocity pressure into actual velocity requires either mathematical calculation, reference to charts or curves, or prior calibration of the manometer to directly show velocity. In practice this type of measurement is usually made with a Pitot tube which incorporates both static and total pressure sensors in a single unit. Essentially, a Pitot tube consists of an impact tube (which receives total pressure. The air space between inner and outer tubes permits transfer of pressure from. Pitot tube and then, through connecting tubing, to the low or negative. When the total pressure tube is connected to. See. Since the Pitot tube is a primary standard device used to calibrate all other air velocity measuring devices, it is important that great care be taken in its design and fabrication. In modern Pitot tubes, proper nose or tip design - along with sufficient distance between nose, static pressure taps and stem - will minimize turbulence and interference. This allows use without correction or calibration factors. All Dwyer Pitot tubes are built to AMCA and ASHRAE standards and have unity calibration factors to assure accuracy. To insure accurate velocity pressure readings, the Pitot tube tip must be pointed directly into (parallel with) the air stream. As the Pitot tube tip is parallel with the static pressure outlet tube, the latter can be used as a pointer to align the tip properly. When the Pitot tube is correctly aligned, the pressure indication will be maximum. Because accurate readings cannot be taken in a turbulent air stream, the Pitot. To insure. precise measurements, straightening vanes should be located 5 duct diameters. Pitot tube. How to Take Traverse Readings. In practical situations, the velocity of the air stream is not uniform across. Friction slows the air moving close to the walls. To obtain the average total velocity in ducts of 4" diameter or larger, a series of velocity pressure readings must be taken at points of equal area. A formal pattern of sensing points across the duct cross section is recommended. These are known as traverse readings. Fig. 4 shows recommended Pitot tube locations for traversing round and rectangular ducts. In round ducts, velocity pressure readings should be taken at centers of equal concentric areas. At least 2. 0 readings should be taken along two diameters. In rectangular ducts, a minimum of 1. Actual velocities for each area are calculated from individual velocity pressure readings. This allow the readings and velocities to be inspected for errors or inconsistencies. The velocities are then averaged. By taking Pitot tube readings with extreme care, air velocity can be determined within an accuracy of ±2%. For maximum accuracy, the following precautions should be observed. Duct diameter should be at least 3. Pitot tube. Located the Pitot tube section providing 8- 1/2 or more duct diameters. Pitot tube free of. Provide an egg- crate type of flow straightener 5 duct diameters upstream. Pitot tube. Make a complete, accurate traverse. In small ducts or where traverse operations are otherwise impossible, an accuracy. Pitot tube in center of. Determine velocity from the reading, then multiply by 0. Calculating Air Velocity from Velocity Pressure. Manometers for use. Pitot tube are offered in a choice of two scale types. Some are made specifically. They are correct for standard air conditions, i. F, barometric pressure of 2. Hg. To correct the velocity reading for other than standard air conditions, the. It may be calculated if relative humidity, temperature. Most manometer scales are calibrated in inches of water. Using readings from such an instrument, the air velocity may be calculated using the basic formula. With dry air at 2. Air Velocity Flow Charts. For partially or fully saturated air a further correction is required. To save time when converting velocity pressure into air velocity, the Dwyer Air Velocity Calculator may be used. A simple slide rule, it provides for all the factors needed to calculate air velocity quickly and accurately. It is included as an accessory with each Dwyer Pitot tube. To use the Dwyer Calculator: Set relative humidity on scale provided.
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