Common Sense Maintenance

Issue No. 48–November, 1994

Most of us make decisions based on common sense. But sometimes, what seems like the most sensible thing to do is not necessarily the best thing to do. Take leak locating, for example. If you look at a monitoring system printout, you'll often see that the pressure transducers at the end of the route have the lowest readings. So, you'd think it would make sense to start leak locating out there, right?

Wait...not so fast. There's more than one reason why those transducers could read low. The most important one is low delivery pressure. A major leak in your air pipe will drop pressure in all the cables—especially those farthest from an air source. So, if you want to make the most efficient use of your time and raise the delivery pressure to all of the cables on a route, first check out the air pipe.

This Gazette article will explain how you can perform a systematic and routine examination of your air pressure delivery system and gather some important information that will make your job easier and your leak locating time more productive.

The Merits of Pipe Purification
Air pipe purification is one of the most important tasks performed in an air pressure system. It is a systematic way of checking air consumption, section by section, along an entire pipe route. It's similar to what a bank does, for example, when it transports money between two branch offices. First they count every dollar before they have it delivered, and then count it again when it reaches its destination. If the two amounts are not the same, they know they've lost some cash somewhere along the way.

In an air pipe system, you measure the amount of air flow at two locations on the pipe. Assuming there are no manifolds or pipe "Ts" between them, the flow rates should be the same. If they're not, there is a leak or something else—like a cheater hose or unrecorded (ghost) manifold—that is consuming air from the pipe somewhere between the two locations.

The process of purifying an air pipe is the foundation of an efficient proactive maintenance program. It makes it possible for you to verify the location of all air consumers (including leaks) on an air pipe run and identify each of the pneumatic sections on the route. It also results in two big payoffs: (1) improvement of the air supply system (reduced flows and increased delivery pressure to the cables in the field), and (2) reduction of maintenance hours spent on the routes. In the long run you can be assured of having a sound delivery system in place, and you can allocate maintenance hours where they're most needed--on the system's most damaging leaks.

Old vs. New Methods
The game plan for purifying air pipes varies depending upon the technique and equipment used. The old way of purifying a pipe requires the use of two crews playing leapfrog from pressure reading to pressure reading, installing air pipe shutoff valves in the pipe at each manifold and pipe junction, and buffering the cables with nitrogen tanks. The whole process is disruptive to the system and can take days or even weeks to complete if there are a lot of trouble calls coming in.

You'll be glad to hear that there is a much easier and more efficient way to purify an air pipe. This method incorporates the use of Flow Finders. The procedure itself is easily performed with two technicians, but one person is capable of doing the job.

Flow Finders, which are available in 0-9.5, 0-19, 0-47.5, and 0-95 Standard Cubic Feet per Hour (SCFH) flow ranges, are permanent installations in the air pipe system. They can be left in place after the pipe has been purified to provide valuable tools for flow analysis.

The primary advantage of using Flow Finders to purify an air pipe is that there is no need to shut off flow into a pipe section and buffer cables to maintain pressure protection. Flow Finders allow the entire volume of air to flow through the system, even when taking a reading using the hand-held Flow Gauge. A Flow Finder can be installed in minutes, resulting in considerably less disturbance to the air pressure system during the purification process.

The following items are required to perform the Flow Finder method of pipe purification:

• Flow Gauge attaches to the Flow Finder sampler valves to provide an accurate flow reading)
• Flow Finders (a variety of flow ranges should be on hand)
• Flow Finder Analysis Checklist (for recording locations and flow reading information)
• Stickmaps and other pressure records (for identifying air pipe manifold locations and pipe "Ts")

Getting Down to Business
The following steps summarize what needs to be done to purify a pipe using Flow Finders. The process begins in the central office and continues systematically outward to the end of each pipe section. The figure on the following page illustrates where Flow Finders would be installed along a typical route to perform the purification procedures summarized below.

• Install a Flow Finder (#1 in figure) at the pipe panel in the central office, making sure the flow rate of the device will accommodate the total flow at the panel. Take a flow reading using the Flow Gauge and record the information.

• At the first manifold or pipe junction location in the field, install another Flow Finder of the same range in the air pipe (#2 in figure). If there is a manifold at this location, install the Flow Finder in the pipe on the central office side of the feed to the manifold. Take a flow measurement here to see if it is the same as the flow reading at the pipe panel's Flow Finder.

• If the flow reading here is less than the pipe panel flow, you've got a leak or unrecorded air source between the central office and this Flow Finder. If this is the case, install a Flow Finder in a utility hole approximately halfway back toward the central office and check the flow. The flow measurement there will tell you which way to go nexttoward the central office or toward the field. Continue this process until you've found the cause of the missing flow.
• If the flows add up between the office pipe panel and the manifold, go to the next air pipe manifold or pipe "T" location and install another Flow Finder in the pipe (#3). This time you'll have to subtract the total manifold flow from the flow reading taken at the first manifold location. If the flows don't add up, go back toward the last manifold. Notice in the figure that a fourth Flow Finder (#4) was installed midway between manifolds. It eventually led to the discovery of a cheater hose on the air pipe.
• At pipe "T" junctions, you'll need to install a Flow Finder on each pipe section close to the junction (#5 and #6). The amount of flow into each section should add up to the total flow consumed by the manifold(s) on the individual sections. If it doesn't, simply work your way back to the "T" installing Flow Finders (#7 in figure) until you've located the missing flow.
• Continue placing Flow Finders, recording flow readings, and identifying air consumers along the pipe until the entire route is purified. You'll know that the purification procedure is complete when all the air flow is accounted for.

Summary
Pipe purification is the first step in a thorough, ongoing, proactive maintenance program. If you've taken notes and recorded readings along the way, you'll be able to update your air pressure records to reflect what actually exists in the field. Accurate data is the foundation of a successful proactive maintenance effort.

After the air pipe has been purified, you'll also know that the air pipe delivery system is sound and reasonably air tight. Then you can systematically go after cable leaks—prioritizing the highest flowing manifolds and working on high flowing cables.

As you watch delivery pressure rise and cable pressures improve throughout the system as a result of your efforts, don't be surprised at how successful you are. It's just common sense maintenance.