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Article #6:  Choosing Flow Finder Ranges

July 17, 2006
For those of you who may not yet be familiar with our Flow Finder product line, this Tip of the Week describes the various Flow Finder ranges available and recommendations for selecting the correct one for a particular installation. Flow Finders can be purchased in five flow ranges which are calibrated in Standard Cubic Feet per Hour (SCFH): 0–9.5 SCFH, 0–19 SCFH, 0–47.5 SCFH, 0–95 SCFH and 0–475 SCFH. Selecting and installing the appropriate Flow Finder at a given location is important for ensuring the accuracy of manual flow readings. That's why this article includes some suggestions to help you determine the proper flow range for a particular installation.

Ideally, the average flow being measured should fall within the mid-range of the Flow Finder being installed. However, thanks to the "times two" button located on top of the Flow Gauge—the tool used to manually measure Flow Finder readings—determining flow rates that exceed the Flow Finder's range isn't a problem. For example, let's say that a 0–19 SCFH Flow Finder is installed at an air pipe manifold (or in the incoming port of a Flow Finder Manifold). A flow reading taken with the Flow Gauge is "pegged" (showing the maximum flow rate on the gauge). Depressing the "times two" button in this case drops the needle position back into the reading range, let's say to 12 SCFH. Multiplying the 12 SCFH by two allows the true and accurate flow range of 24 SCFH to be measured.

Reading problems may be encountered when a Flow Finder is installed that accommodates a significantly higher flow rate than the flow being measured. This problem is attributed to the non-linear design of the Flow Gauge. Reading the Flow Gauge is as simple as matching the color of the Flow Finder with the color on the face of the Flow Gauge (see image below).

Flow Gauge Face Scales

For example, a 47.5 SCFH Flow Finder has a blue label. Therefore, the blue scale on the Flow Gauge is used to determine the flow rate. By examining the face of the Flow Gauge (see image below), you can see that the numerical increments are different for each flow range. If a 47.5 SCFH Flow Finder were used to measure a flow of 3 SCFH, for example, it would be very difficult to determine an accurate reading due to the smaller increments associated with a 47.5 SCFH Flow Finder. A better method of measuring lower amounts of flow would be to use a 19 SCFH Flow Finder. This device enables you to use the red scale, which shows a much clearer distinction between measurements (flow rates). In any case, keep in mind that it is very difficult to read flows accurately in the lower 10% of any of the Flow Finder ranges.

Flow Range Recommendations
For each of the hardware and equipment locations listed below, we have recommended the most appropriate Flow Finder to install. If a flow transducer is currently monitoring air flow at any of these locations, either a Flow Finder with the same range should be installed or you may wish to replace the older resistive transducer with a System Studies Manifold Monitoring assembly of the required range. The Manifold Monitoring Assembly contains a 4–20 milliamperes (mA) High Resolution Flow or Dual (pressure/flow) Transducer and a Flow Finder Manifold installed on a stainless steel bracket.

Pipe Alarm Panels.  If you are still using the old-style panels with flow raters, check the flow meter installed on the panel and read the air flow in Standard Cubic Feet per Day (SCFD). If the flow at the pipe alarm panel is under 1200 SCFD or 50 SCFH, install a 47.5 SCFH Flow Finder. If flow is over 1200 SCFD (pegged), install a 95 SCFH Flow Finder. (System Studies also offers an entire line of modular central office panels as possible upgrades for your older equipment. Please refer to the Hardware Products section, or give us a call for additional information.) By the way, the 0–475 SCFH Flow Finder mentioned at the beginning of this article is standard equipment on Power Pipe Panels (for 1" air pipe) supplied by System Studies.

Meter Panels.  A 47.5 SCFH Flow Finder is recommended for most meter/distribution panels. In some smaller central offices, however, a 19 SCFH Flow Finder may more practical.

Air Pipe Manifolds.  Install a 19 SCFH Flow Finder when there are 10 or less cables being fed at a manifold location. If more than 10 cables are being fed, install a 47.5 SCFH Flow Finder. An exception to this rule occurs when there are less than 10 cables, but extremely high air flow are encountered. In this case, a 47.5 SCFH Flow Finder may be installed.

In-line with the Pipe.  The range of the Flow Finder installed in-line on an air pipe should be based on the expected flow rate at the point of installation. This expected flow rate can be determined by measuring the flow a the first Flow Finder on the central office side of the new installation point. For example, let's say that a Flow Finder is being installed in the air pipe at the first air pipe manifold location. Looking back toward the CO, a flow rate of 30 SCFH is measured at the pipe alarm panel. In this situation, a 47.5 SCFH Flow Finder would be the correct range to use.

Hopefully, these examples have clarified what Flow Finder ranges are most suitable for various applications. With any of these suggestions, however, the bottom line is experience. Like anything else, a little experience goes a long way in determining the best range of Flow Finder to install in a particular situation. If Flow Finders are a fairly new addition to your air pressure system, or if you'd just like to find out more about them, please give us a call (800) 247-8255.