The first product designed and manufactured by System Studies back in the late 80s was our Flow Finder™. Today this simple flow measuring device in an integral component in many of our air distribution and monitoring products, as well as a permanent fixture in many telephone operating company cable pressurization systems.

To provide our friends in the field with helpful information about Flow Finders—where they should be installed, how to size them for a particular application, how to read them, etc.—we wrote a series of Flow Finder Tips which first appeared in 1989. Some of the more pertinent ones are reprinted here for your reference. The information they offer is as relevant today as it was when it first appeared. If you are using or installing Flow Finders in your air pressure system, you may want to read through these Tip of the Week articles. You're likely to find some very useful information.

Recently, we've begun to see a renewed interest in the use of Flow Finders for leak locating. This latest spurt in Flow Finder popularity affirms the value of the product for tracking air consumption in a route and providing accurate flow readings. Because many visitors to Airtalk.com may not be familiar with the full capabilities and benefits of Flow Finders, we're posting the most relevant articles from our Flow Finder Tip of Week collection here. The original articles were first mailed to our customers in printed form back in 1989, and eventually reformatted and added to our website in 2006. We think you'll find the information they provide just as helpful and useful today as it was for our customers back then.

Here's some information you may find useful:

• Flow Finders are extremely effective for identifying leaks in the air pipe. The air flow entering a section of air pipe should equal the air exiting. If it does not, you've got one or more leaks in that section of pipe. With Flow Finders we have identified leaks as small as 1 or 2 Standard Cubic Feet per Hour (SCFH).


• Flow Finders are also helpful in verifying flow transducer readings. In fact, flow transducers that are out of calibration may explain the majority of situations where air flow doesn't add up. Having a poor air pressure index (PressureMAP System Quality Index) based upon a bad flow transducer is especially disturbing, considering all the work that goes into improving system indexes.
  
  One thing we would like to stress is that a flow transducer cannot be calibrated in the field. If you find a transducer that is out of calibration, send it back to the manufacturer.


• The Flow Finder should begin to give an accurate reading 5 to 10 minutes after it has been installed. It is important to install the Flow Finder as quickly as possible to reduce the time needed for the system to stabilize. If installed quickly and properly, the Flow Finder can be used to "sectionalize" the air pipe before moving to another location. By sectionalize, we mean verifying total air consumption in a specific length or section of pipe (one defined on both ends by Flow Finders).
  
  For example, we recently isolated a section of air pipe that registered 52 SCFH at one end and 39 SCFH at the other (identifying a pipe leak of 13 SCFH). A Flow Finder placed at the midpoint of this section indicated a flow of 52 SCFH. This information reduced the section of the pipe down from to the field side of the midpoint location (by confirming that the CO side had now leaks). Without the responsive and accurate information provided by the Flow Finder, several additional flow readings at different locations would have been required to sectionalize the pipe.

Please give us a call if you have any questions about the information in this Tip of the Week, about Flow Finders in general, or any of our other products and services.

A concern that has been voiced in the past about our Flow Finders is that they restrict air flow. Some people believe that this restriction is significant enough to reduce cable pressure and actually jeopardize air pressure protection in the cable. Although we don't agree with this assessment, we recognize that it's a very real concern. Therefore, in this Flow Finder Tip we'd like to clarify our views on restriction and try to eliminate any uneasiness among those of you who might be using or are planning to use Flow Finders.

Flow Finders contain a calibrated internal orifice which creates a very slight, but measurable pressure differential as air flows through the device. Two tank valves installed on top of the Flow Finder above the orifice provide the means of measuring this differential. One valve measures uphill or incoming pressure; the other measures the downhill pressure on the back side of the orifice. This slight pressure differential is then converted by the Flow Gauge into a highly accurate flow rate. Because you can actually see the orifice inside of the Flow Finder, the question of a restriction has been raised. We acknowledge that a slight restriction does occur; otherwise, there could be no pressure differential to be measured.

You may not realize that this same principle pertains to resistive flow transducers which, of course, have been in use for many years in the telco industry. An orifice in the flow transducer—one that is not visible to the eye—causes a slight restriction in order to measure flow. The orifice that causes the pressure differential in a Flow Finder has approximately the same pressure drop as the orifice used in a standard flow transducer. In fact, all Flow Finders meet Bell Communication Research (Bellcore) Technical Reference TR-TSY-000183 for acceptable pressure drop. This acceptable pressure drop is less than or equal to the pressure drop created by a flow transducer.

One way to reduce concerns about Flow Finders restricting air flow and lowering cable pressure is to recall when you installed flow transducers. Did you see any drop in cable pressures? Probably not. And because Flow Finders and flow transducers use the same concept to measure flow, you won't see a drop in cable pressures when installing Flow Finders. There are a number of devices already installed in your system that generate a greater pressure drop than Flow Finders. For example, check valves, air pipe manifolds, and 3/8-inch tubing all impact the cable pressurization system. However, the effect is so small, that removing them accomplishes absolutely nothing.

When a drop in delivery pressure occurs in a pressurization system, we can almost guarantee that it's caused by a high flow condition (air pipe leaks or cheater hoses) and not the hardware installed in the system. Using Flow Finders on high flowing routes allows you to track down leaks and cheater hoses—helping to raise pressures, not bring them down.

Now that we've provided you with some information about the restriction issue, we hope you will try Flow Finders and see for yourself what takes place. Call us and we'll be glad to discuss arrangements for a field trial and share some eye-opening experiences we've had with technicians who have used the product. Also, don't hesitate to let us know if you have any questions about the information in this Tip of the Week, the Flow Finders in general, or any of our other products and services.

As some of you may know, System Studies Incorporated has been involved in the engineering of cable pressurization systems for a number of years. In fact, our engineers and drafters have designed systems for over 2300 offices in the United States. From calculating Optimum Air Usage (OAU) figures to providing our most comprehensive Level 2 Engineering, our Technical Services Department personnel are experts in all facets of cable pressurization system engineering.

What's the association between our Technical Services Department and Flow Finders? Our engineers have developed two symbols for Flow Finders which appear on the engineering documentation that we provide to our customers. One of these symbols, a solid triangle, is used to indicate the locations of installed Flow Finders on stickmaps. When completing stickmaps for an office which contains Flow Finders, our Technical Service Department regularly uses this symbol. They recommend that once you have installed Flow Finders in an office, your stickmaps should also be updated to include the symbol.

The image below illustrates the use of the new symbol in a typical PressureMAP stickmap. It is located in the Title Block along with other stickmap symbols. On the map itself, the symbol points to the actual manhole (or manhole name/number) where Flow Finders are installed.

Flow Finder Engineering Symbols (continued)

When contracted for Level 2 Engineering, our Technical Services Department provides high quality Construction Workprints (in addition numerous other important engineering documents). A second Flow Finder symbol has been designed for this type of documentation. If Flow Finders are going to be installed in an office that we're engineering, this symbol will be included on all appropriate Construction Workprints. We recommend that you include the symbol on your workprints if you're planning to install or have Flow Finders installed in your area.

As you can see in the workprint example below, Flow Finders are indicated by using the letters "FF" enclosed within a circle. In addition, the letters "A" and "B" are positioned next to the respective Flow Finder symbols. These letters reference the placement notes (lower left corner of workprint) that identify the range of the Flow Finder to install.


When any type of hardware revision is made in a cable pressurization system, the appropriate engineering documentation should be updated to indicate the changes. If you have installed Flow Finders in your office or your future plans include them, please use the symbols we introduced in this Flow Finder Tip of the Week. If you have any questions regarding the use of these symbols, or if you're interested in finding out more about our engineering services, please give us a call at (800) 247-8255.

In our first Tip of the Week we mentioned that Flow Finders help technicians verify resistive flow transducer readings. In this article we'd like to explain the specific method we use to determine whether or not technicians can rely on these flow transducers for accurate readings.

Are your resistive flow transducers calibrated? It has been our experience that when flow transducer readings at air pipe manifolds don't add up to the flow measured at the pipe alarm panel, one or more bad flow transducers may be the problem. This possibility becomes even more probable if the pipe alarm panel reads 45 Standard Cubic Feet per Hour (SCFH), for example, and the total sum of the flow readings in the field is only 20 SCFH. If the cause of this discrepancy is not a bad flow transducer, it could be a leak in the air pipe, a cheater hose, or a ghost manifold. Whatever the reason, Flow Finders will help to solve the mystery.

How do you determine what's causing the difference in flow readings? The simplest and quickest way is to install Flow Finders at key locations on the pipe route. We recommend that you install a 0-47.5 SCFH or 0-95 SCFH Flow Finder at the pipe alarm panel (the correct one depends on the pipe's current flow rate) and a 0-19 SCFH Flow Finder between the air pipe and each of the manifolds. That's assuming, of course, that you are using old style air pipe manifolds and not the System Studies Flow Finder Manifolds, which are equipped with built-in Flow Finders. The Flow Finder at the pipe alarm panel will verify the reading provided by the panel's flow transducer. If the readings aren't the same, part—or possibly all—of the problem can be identified before you even leave the office. The Flow Finders in the field can then be used to verify individual manifold flow transducer readings and whether or not there are other problems in the system.

In addition, PressureMAP users may want to check the pipe alarm panel flow transducers on routes that have a low System Quality Index (SQI). By investigating the flow monitoring device, you may find that the cause for a low SQI is something other than a leak. Think of all the money you'd save by not looking for a leak that doesn't exist!

If you have any questions on how Flow Finders can be used in your area, give us a call at (800) 247-8255. We'd appreciate hearing from you.

In our first Tip of the Week we mentioned that Flow Finders help technicians verify resistive flow transducer readings. In this article we'd like to explain the specific method we use to determine whether or not technicians can rely on these flow transducers for accurate readings.

Are your resistive flow transducers calibrated? It has been our experience that when flow transducer readings at air pipe manifolds don't add up to the flow measured at the pipe alarm panel, one or more bad flow transducers may be the problem. This possibility becomes even more probable if the pipe alarm panel reads 45 Standard Cubic Feet per Hour (SCFH), for example, and the total sum of the flow readings in the field is only 20 SCFH. If the cause of this discrepancy is not a bad flow transducer, it could be a leak in the air pipe, a cheater hose, or a ghost manifold. Whatever the reason, Flow Finders will help to solve the mystery.

How do you determine what's causing the difference in flow readings? The simplest and quickest way is to install Flow Finders at key locations on the pipe route. We recommend that you install a 0-47.5 SCFH or 0-95 SCFH Flow Finder at the pipe alarm panel (the correct one depends on the pipe's current flow rate) and a 0-19 SCFH Flow Finder between the air pipe and each of the manifolds. That's assuming, of course, that you are using old style air pipe manifolds and not the System Studies Flow Finder Manifolds, which are equipped with built-in Flow Finders. The Flow Finder at the pipe alarm panel will verify the reading provided by the panel's flow transducer. If the readings aren't the same, part—or possibly all—of the problem can be identified before you even leave the office. The Flow Finders in the field can then be used to verify individual manifold flow transducer readings and whether or not there are other problems in the system.

In addition, PressureMAP users may want to check the pipe alarm panel flow transducers on routes that have a low System Quality Index (SQI). By investigating the flow monitoring device, you may find that the cause for a low SQI is something other than a leak. Think of all the money you'd save by not looking for a leak that doesn't exist!

If you have any questions on how Flow Finders can be used in your area, give us a call at (800) 247-8255. We'd appreciate hearing from you.

We have found that one of the most commonly used applications for Flow Finder equipment has been to check the calibration of resistive flow transducers. In most of the Flow Finder product demonstrations that we've conducted over the years, one or more of the flow transducers installed on a route was found to be inaccurate or defective. While the importance of flow transducer accuracy has surprisingly been downplayed by manufacturers, we would like to give our reasons why accurate flow transducers are essential in analyzing the system and dispatching technicians. The most important reasons are:

• The quality of a cable pressurization system is being based more and more on air flow per sheath mile of cable or per tube (3/8" tubing from a manifold or distribution panel to a cable). A poor System Quality Index (SQI) for a route can result in labor hours being expended to improve the system. An obviously inefficient use of labor hours would be to work on a good route that merely appears "bad" because of an inaccurate reading by a faulty flow transducer.
  
  A flow transducer reading can be verified by installing a Flow Finder on the air pipe at the transducer location. The Flow Finder will provide an accurate flow rate that can be compared with the transducer reading.
• When a flow transducer indicates a flow increase at an air pipe manifold, a technician is typically dispatched to the field to find the cable leak. But the indicated flow increase may also be the result of a bad flow transducer, trouble on the pair, an incorrect transducer flow range input into the monitoring pair, or the installation of a transducer with an incorrect flow range.
  
  To begin looking for a leak without first verifying the accuracy of the flow transducer is both inefficient and frustrating. For comparison, think about the standard procedure for pressure transducer dispatches. When a pressure transducer reading drops, do you trust the reading or do you take a manual pressure reading at the transducer location?
  
  The same thing should apply to flow transducer readings. While you are at the flow transducer location, use a Flow Finder and Flow gauge to reconfirm that you are not chasing ghosts.
• When the sum of the air pipe manifold flow transducer readings does not add up to the total flow at the pipe alarm panel, something is wrong. There are several possible reasons for this: 1) there's a leak somewhere in the air pipe, 2) a ghost manifold or cheater hose is installed somewhere on the pipe, 3) one of the flow transducers is bad (inoperative or inaccurate), or 4) the air pipes are transposed.
  
  The important thing to remember is that it is NOT OK to have flows that don't add up. For example, when the sum of the manifold flows on a route is 20 Standard Cubic Feet per Hour (SCFH) and the pipe alarm panel is flowing 50 SCFH, you've got a problem. You can't expect the index on this route to be accurate or your dispatching to be effective without first determining where the 30 SCFH is going.

So, whenever you encounter a situation where air flows don't add up, find out why. A few Flow Finders installed on a route will tell you more about your system in one afternoon than you ever thought possible.

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).

Choosing Flow Finder Ranges (continued)

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.

If you have been reading the previous Tip of the Week articles, you're probably beginning to see the value of these devices for leak locating and purifying air pipes. Not only do they help you determine whether or not you have a leak, they also provide a positive indication of the size of the leak. In this Tip we'll discuss two applications that pertain to locating leaks in underground and aerial air pipe.

Problem 1: An air pipe goes aerial for almost half a mile before it reenters the underground. A squirrel problem exits in the area (damn varmints!), and a leak is suspected in the aerial section. How do you verify that there is a leak?

Solution: Installing Flow Finders where the air pipe exists and reenters the underground (see Figure 1) will allow you to measure air flow in Standard Cubic Feet per Hour (SFCH). If the flow at these two locations are equal, a leak does not exist in the aerial air pipe. In addition, with this installation the flows can be verified any time a leak is suspected in the air pipe.



Problem 2: A leak is suspected in an underground air pipe where the pipe T's. How can you determine if there is a leak or no leak in this area?

Solution: Two of the recommended locations for installing Flow Finders are at air pipe T's and manifolds (Figure 2). If the flow at each of the legs is equal to the flow at the air pipe manifold, there are no leaks. For example, Flow Finder A should equal Flow Finder B, and Flow Finder C should equal Flow Finder D. If the flow readings don't match up (as in Flow Finders A and B), you've got a leak in that section of air pipe.

Flow Finders/Pipe Purification (continued)



If you have any questions about how the Flow Finders can be used in your area, give us a call at (800) 247-8255. We'd appreciate hearing from you. And if you're already using Flow Finders and the Flow Gauge for leak locating in various situations, we'd like to hear about them so we can share your findings with our readers.

In each Tip of the Week article we have tried to explain one or more applications for the Flow Finder and Flow Gauge. In this Tip we'll discuss a time-saving and convenient feature available for use with each of the various Flow Finder ranges.

As discussed previously, determining air flow in Standard Cubic Feet per Hour (SCFH) with the Flow Finder equipment is achieved by first measuring the pressure differential created by the Flow Finder's internal calibrated orifice. This differential is measured by the Flow Gauge using the two tank valves installed on top of the Flow Finder. Because of the simple way in which the air pressure differential is measured, we have been able to develop a component which extends the remote manual measurement capability of the Flow Finder. This component, call a "high valve," is available for all original four Flow Finders as well as the high range 475 SCFH Flow Finder. And, as is the case with the normal reading of a Flow Finder, a remote manual reading does not cause any restriction in the air flow.

To simplify the reading process, Flow Finders and high valves are color-coded (as shown below) to correspond to the colored flow range scales on the Flow Gauge (see illustration in Tip #6, Choosing Flow Finder Ranges). If using a 0-475 SCFH Flow Finder, just use the blue scale for your flow measurements and multiply the measured value by ten.



A remote manual reading is accomplished by connecting two 3/8" plastic tubes from the Flow Finder to the high valve (as shown in the next illustration). The high valve is equipped with the proper spacing between the valve and the center screw assembly to allow for easy attachment to the "sampler" component of the Flow Gauge. In addition, the high valve includes a "polarization collar" which makes it impossible to seat the sample incorrectly. As a result, you will receive an accurate reading every time.

Because air pressure, and not air flow, is passed through the tubing, the distance between the Flow Finder and high valve is not limited. We've experimented with a working distance of 30 feet, but there is no reason why the distance cannot be greater.

Flow Finders and High Valves (continued)



The high valve can be used in several applications:

1. In a manhole where a flow reading at at pipe tee is required, but entry is difficult. A wet or deep manhole is a good example of this situation. The high valve can be placed in the manhole collar for easy reading.
2. As a "down valve" for aerial air pipe. The high valve could be placed on a pole at the midpoint of an aerial section and read from the ground.
3. At a pedestal where conduct is run into a manhole. The high valve can be placed at the pedestal to obtain a reading.

Flow Finders and High Valves (continued)


These are just a few of the applications for the Flow Finder high valve. If you would like to try using this handy device, give us a call. High Valves can be ordered separately as Part No. 9800-3010 or in a box of six as Part No. 9800-3030. For a typical installation, you also need to purchase the Flow Finder(s), twin Santoprene tubing (Part No. 9800-3031) and jaw pinchers (Part No. 9800-3510).

In this Tip of the Week article, we'd like to discuss why Flow Finders measure air flow more accurately than a portable flow rater. We've been asked repeatedly over the years why readings from a portable flow rater at an air pipe manifold never add up to the flow indicated by the flow transducer. There's a logical explanation for this, and we can prove it with a simple experiment.

When a flow rater is used to take a flow measurement at an air pipe manifold, its air chucks must first be installed on the manifold's pressure testing valves. Then, a shutoff valve on the manifold is closed and the air is redirected through the flow rater (as shown in the figure below).



This rerouting of air flow is the actual cause of inaccurate readings. Because the air must travel through the flow rater, the air chucks, the pressure testing valves and the tubing, it is restricted considerably. This restriction reduces or slows down the "real" flow and causes a reading that is less than accurate. So, the higher the flow being measured, the greater the inaccuracy. In fact, it's not uncommon to have a flow transducer at a manifold indicate a flow of 18 Standard Cubic Feet per Hour (SCFH), while the flow rater shows a flow of 10 or 11 SCFH.

Because the Flow Finder uses a different concept for measuring air flow, this rerouting of air doesn't occur. The Flow Finder simply creates a slight pressure differential over a calibrated orifice, which can then be measured with the Flow Gauge (as shown in the illustration on the next page).

Flow Finder Vs. Portable Flow Rater (continued)


In order to see the discrepancies that occur when using a portable flow rater versus a Flow Finder, you many like to try the following experiment. Install a 0–19 SCFH Flow Finder either before or after the flow transducer on a manifold. Hook up the Flow Gauge to the Flow Finder. Now read each individual cable with a portable flow rater. As each cable is read, you'll discover that the flow indicated by the Flow Finder will be reduced each time air is rerouted through the portable flow rater (figure below).

The Perfect Candidate
When asked to set up a field trial for Flow Finders, one of the first things we do is evaluate routes to determine the best one for the installations. If PressureMAP is being used in the area, this task is fairly easy. What we do typically is pull up the System Quality Indexes (SQIs) by route for the wire center that has the worst SQI. A route with an index less than 60 (90 is the standard) is a perfect candidate for the installation of Flow Finders.

What we'll often see on the worst route is that the flow rate at the pipe alarm panel is much higher than the listed Optimum Air Usage (OAU). For example, you might see 50 Standard Cubic Feet per Hour (SCFH) at the panel with an OAU of 10 SCFH. This type of flow discrepancy will drop your SQI every time.

What Good Is It?
What good is a pegged flow transducer? Not much good at all, especially when the flow transducer at the pipe panel is "maxed out." With a pegged flow transducer, there's no way to tell if you're chasing a flow of 50 SCFH, for example, or 80 SCFH. Without knowing the true flow rate, it is impossible to determine the size of the problem and identify what you're chasing. The same is true for pegged flow transducers at air pipe manifolds.

One of the major advantages of using System Studies' Flow Finders and Flow Gauge is that the Flow Gauge has a "times two" button. This feature enables accurate flow readings to be taken at any Flow Finder location, even if the flow rate exceeds the flow range of the device. For example, by using the "time two" button, a 0-47.5 SCFH Flow Finder can accurately measure flow rates up to 95 SCFH.

What's the Problem Here?
Whenever you find a big difference between a Flow Finder reading and a flow transducer reading, there may be a simple explanation and fix. The first thing to do is check to see that the flow range entered into the monitoring system for the flow transducer is correct. For example, a 0-19 SCFH flow transducer inputted as a 0-9.5 SCFH will only indicate half of the actual air flow.

Want More Information?
If you'd like to find more about using Flow Finders to leak locate and purify air pipes in your system, there are some interesting and informative articles online here at AirTalk.com. Simply click on the Home button located on the bottom of this page, then the Documentation link, then Newsletter Articles. Many of the articles there address one or more uses for Flow Finders. If you're interested in viewing the various ranges of Flow Finders available and their respective System Studies Part Numbers, go to our 2006 Purchasing Guide (also located in the Documentation section).

Effect of Pipe Pressure Variations on Flow Gauge Accuracy
In each of our Tip of the Week articles we have tried to provide valuable information about the function and use of our Flow Finders™ and Flow Gauge™. The more informed you are in regard to these measurements tools, the more efficient you will become when measuring flow. One situation in which the accuracy of Flow Gauge readings can be affected is when an air pipe system experiences major drops in pressure. Therefore, in this Tip of the Week we'll discuss how low pipe pressure can impact Flow Finder readings.

As you're probably aware, an air flow reading can be determined by using System Studies' Flow Gauge in conjunction with a Flow Finder. The Flow Gauge converts the pressure differential created by the Flow Finder's calibrated orifice into an accurate flow rate. The flow rate indicated by the Flow Gauge is based on a pipe pressure of 9.0 Pounds per Square Inch (PSI). Therefore, a reading taken by a Flow Gauge in an air pipe with 9.0 PSI will always be accurate. If the pipe pressure is over or under 9.0 PSI, however, readings will be influenced.

For example, if a Flow Gauge indicates a flow reading of 50 Standard Cubic Feet per Hour (SCFH) and the pipe pressure is 6.0 PSI, the Flow Gauge reading will be higher than the actual or true air flow rate. Why? When the pipe pressure is 6.0 PSI, air molecules are less compressed, enabling them to pass through the Flow Finder orifice at an accelerated rate. And remember, the Flow Gauge is calibrated to read pressure differential at 9 PSI. So, a lower pipe pressure at the Flow Finder location would mean that the flow rate indicated by the Flow Gauge is somewhat higher than the actual reading. Conversely, a pipe pressure of 11 PSI, for example, would result in more densely compressed air molecules forcing their way through the orifice. This results in a lower Flow Gauge reading when compared with the true flow rate.

To help determine accurate flow readings with the Flow Gauge at different air pipe pressures, we have compiled the conversion chart on the next page. You can see that a Flow Finder reading taken at an air pipe that has a delivery pressure of 6.0 PSI requires an offset calculation of 0.87. So, if the Flow Finder reading is 50 SCFH, the actual or accurate flow reading will be 43.5 SCFH (50 x .87 = 43.5 SCFH). It is important to note that, in most cases, the conversion process will be unnecessary except in pipes that have significant changes in pressure and/or high flow rates.

See Conversion Chart on next page.

Flow Finder Vs. Portable Flow Rater (continued)


Hopefully, this article has explained how it could be possible for one Flow Finder at a pipe alarm panel to read 60 SCFH (with an input pressure of 9 PSI) and another Flow Finder installed in the air pipe at a manifold location to read 65 SCFH (with an input pressure of 7 PSI). The difference in readings is the result of air pressure, not flow. Using the table above, you can see that the converted flow rate for the Flow Finder at the manifold location would be 59.8 SCFH. This reading accurately represents the true flow rate at this location.

If you have any questions regarding Flow Gauge conversion, or if you would like any additional information on the Flow Finders and Flow Gauge, please give us a call or drop us some email.

In our previous Tip of the Week articles we've discussed using Flow Finders™ in conjunction with flow transducers on a route. Although this is the most common application, we'd like to examine the use of Flow Finders on a route that does not have flow transducers.

If you don't already have flow transducers installed in your system, there are a number of reasons why Flow Finders may be the most logical alternative: 1) Flow Finders do not require engineering; 2) they are quick to install; 3) they are less expensive than flow transducers; 4) Optimum Air Usage (OAU) calculations can be determined for Flow Finders; 5) and, unlike flow transducers, Flow Finders can be used for identifying leaks in the air pipe. In fact, this is one of their primary functions. Finally, they provide more accurate measurements for chasing air flow.

Installing Flow Finders to use as the only flow measuring devices on a route involves purifying air pipes. Using Flow Finders to purify a pipe identifies the major problems along the route, the ones that reduce delivery pressure. When purifying air pipe, Flow Finders should be installed at the following locations: Pipe Alarm Panels, air pipe (in line), air pipe junctions and air pipe manifolds.

Flow Finders measure air flow and help to localize an area of search when leak locating. For example, let's say that a technician is dispatched to leak locate on a route that has recently been purified with Flow Finders installed at the locations listed above. Figures 1, 2 and 3 show examples of how the technician can take flow readings at the central office and in Manhole B to narrow the area of search.

Figure 1 shows readings of 30 SCFH on the pipe and 18 SCFH at the manifold in Manhole B. A reading of 60 SCFH was measured at the Flow Finder in the central office. Since 30 SCFH is coming into the manhole and 60 SCFH is leaving the central office, a flow of 60 SCFH can be estimated for Manhole A. That's assuming, of course, that there are no new pipe leaks. Visiting Manhole A reveals a reading of 60 SCFH at the Flow Finder on the pipe. The Flow Finder located on the manifold records a reading of 30 SCFH. This high flow indicates a major leak on the cable. Therefore, the area of search is narrowed to the cables in Manhole A.

Using Flow Finders on a Route That Does Not Have Flow Transducers (continued)

The Flow Finder readings in Figure 2 indicate that there is 23 SCFH on the pipe and 18 SCFH in Manhole B. Another Flow Finder reading in the central office reveals that 60 SCFH is heading toward the field. A visit to Manhole A for a quick reading at the Flow Finder on the air pipe shows that there is still 60 SCFH flowing through the pipe. Another reading of 6.5 SCFH is taken at the Flow Finder located on the manifold. These two readings indicate that 53.5 SCFH should be flowing into Manhole B. However, the 23 SCFH reading obtained at Manhole B narrows the area of search between Manholes A and B. In this example, there is a section leak consuming approximately 30 SCFH of air.


Figure 3 displays a reading of 53.5 SCFH on the pipe and 18 SCFH in Manhole B. With the reading of 60 SCFH at the central office, a loss of 6.5 SCFH can be estimated between the central office and Manholes A and B. Compared to the total flow, this low amount of flow is insignificant. However, the flow going toward the field is important. By subtracting the readings obtained at Manhole B (53.5 SCFH minus 18 SCFH), it is calculated that 35.5 SCFH should be flowing to Manhole C. Visiting Manhole C reveals a reading of only 3 SCFH at the Flow Finder at the manifold. Therefore, the area of search is narrowed between Manhole B and Manhole C.


These examples demonstrate how practical Flow Finders are in narrowing down an area of search. They are not a substitute for flow transducers, and we're not suggesting that you replace your flow transducers with them. But, if you have a route without any flow measuring devices installed, Flow Finders are an alternative worth consideration.

Every once in a while, we'll get an inquiry regarding the pressure drop across the calibrated orifice of our Flow Finders. In order to give you a better idea of how insignificant the pressure drop is, we'd like to show you some data from our testing process. At System Studies we use Water Column in Inches (or Inches W.C.), which is a common measurement of pressure, to illustrate the pressure drop of the devices. An Inch W.C. is the pressure necessary to cause water to rise one inch in a tube or manometer.

The maximum pressure drop across a System Studies Flow Finder of any range is 5.2 Inches W.C. This is an extremely minute pressure drop, the equivalent of 0.188 Pounds per Square Inch (PSI).

Following is a table showing some typical Flow Finder readings, with the pressure drop converted from Inches W.C. to Pounds per Square Inch. Note that the flow for each Flow Finder range is measured in Standard Cubic Feet per Hour (SCFH).

		0-9.5 SCFH	0-19 SCFH	0-47.5 SCFH	0-95 SCFH
Inches W.C.	PSI	Flow Finder	Flow Finder	Flow Finder	Flow Finder
0.0	0.0	0.0	0.0	0.0	0.0
1.0	0.036	4.2	8.3	20.8	41.7
2.0	0.072	5.9	11.8	29.5	58.9
3.0	0.108	7.2	14.4	36.1	72.2
4.0	0.145	8.3	16.7	41.7	83.3
5.2	0.188	9.5	19.0	47.5	95.0

From the table above we can see, for example, that a 0-9.5 SCFH Flow Finder, when reading 5.9 SCFH, is creating a pressure drop of only 0.072 PSI. This is only two Inches W.C.

The table also shows that when any of the Flow Finders are reading full scale, there is a 0.188 PSI drop across the calibrated opening. Therefore, the pressure drop across the Flow Finder will be anywhere in the range from 0.0 PSI to 0.188 PSI, or no more than 5.2 Inches W.C.

If you have any further questions regarding the pressure drop in Flow Finders, or Flow Finders in general, please give us a call.