PAT REPORT PRACTICAL. AVAILABLE TECHNOLOGY
Key to reliable exhaust emissions data Balston, I nc.'s glass-impregnated filter protects delicate, production on-line analyzers and satisfies the monitoring needs of both instrument and automobile manufacturers With the advent of Federal standards, the need for accurate vehicle emissions data has become as much a part of automotive development as the need for data generated at the test track. But despite their complexity and, in many cases, their size, analytical instruments used in emissions testing remain extremely delicate pieces of equipment whose functional parts must be adequately protected if they are to operate reiiably and produce the data required. Instrument manufacturers, as well as end users, have found that good protection of their analytical instruments need not be expensive and ^^*..^11.,
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-increased sales for manufacturers, decreased downtime for end usersin addition to more reliable data. Instrument makers Dennis A. Mach, vice-president of the Instrument Division of Heath International, Inc.-one of the major emissions test systems suppliers to the auto industry-says, ',We have good evidence that our constant volume samplers and analytical benches operate significantly longer without downtime caused by contamination since we started using a relatively inexpensive but remarkably efficient filter to protect critical parts." The filter Mach referred to is a tube constructed of borosilicate glass microfibers bonded witt I epoxy resin manufactured by Balston, Inc. of Lexington, Mass.
Heath International's Mach "filter protects critical parts 790
Environmental Science & Technology
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valves. However, these paper filters provided protection against particulate matter only down to about 5 in size. Since contaminants that could foul the instruments often are smaller than 1 p in size, there was a potential reliability problem. i t was a serious threat since one of Heath's strongest selling points to customers is the reliability of its instrument systems. After some searching and quite a bit of testing, Heath discovered the Balston filter. Tests confirmed that these filter units were capable of a retention efficiency not obtainable with other filters, even those costing considerably more. I n addition, the fact that Balston filter tubes could be replaced quickly and easily in the field appealed to Heath, since the company stressed easy serviceability of its systems. Heath now recommends Balston filters on all its new units and has suggested that customers with older units switch from the paper filters to Balston tubes. "We have found." Mach reports, "that with Balston filters in place, there is considerably less downtime . . . . . . . ana tar less cleaning required on all ourequipment."
pany with evidence that these unique filters in emissions test equipment make a big differer i c e in instrument performance. In fat:t, if there is any trend toward uniforin i t y in the emissions test instrumrrnt field, despite the diversity of equ ipment used, the number of manufac:turers building it and the number of companies using it, it would appear to be in the selection of Balston filters. One by one over the last two years . . . or so, more and rnore originai equipment manufacturi?rs and end users have been install ing these filters on their emissions te St equipment-usu. Other instrument suppliers For the world's largest builder of ally after first tryii14- some other filter chemiluminescent gas analyzers, and finding it ncIt efficient enough, Therm" ...l...." Flertmn _."l.._.. n-.f Waltham M i + too costly, or both. the problem of finding the proper filHeath, for example, builds all custer was, perhaps, more difficult than tom-engineered systems, from single test units-such as constant volume samplers-to completely integrated analytical test benches capable of performing several vehicle exhaust emissions tests. Heath buys components from a host of manufacturers after first carefully testing and evaluating them, and constructs what Dennis Mach describes as "the best possible package" to meet a specific customer need. Like many other instrument buildChrysler Corp's Lane ers, Heath originally used 7-cm "filter eliminates downtime paper wafer filters on its test equipproblems" ment to protect critical pumps and
Heath's. Thermo Electron was producing a new analyzer that would be used in the auto industry for exhaust tests, as well as by utilities and government agencies monitoring stack emissions. The filter used on the sample line not only had to be efficient, but it had to have a long service life, have good resistance to gases and corrosion, provide a minimum pressure drop, and be compact enough to fit into their design. Moreover, it had to meet very strict cost parameters. After looking at several likely filters available, Thermo Electron production and engineering people selected a Balston filter. David Brown, manufacturing manager, noted that, "When it comes to cost. compactness and filtering efficiency, the Balston filter had the others beat." Thermo Electron now uses these filters on its full line of chemiluminescent gas analyzers, varying the Balston model according to sample conditions. Several other prominent instrument suppliers to the auto industry, including Sun Electric of Chicago; Air Monitoring, I n c . , a division of Ethyl Corp.; Beckman Instruments; Barnes Engineering; and Hamilton Standard Division of United Aircraft have specified Balston filters on their auto emissions test equipment for some time now. And in the field of continuous sampling gas chromatographs, one of the best known and most widely respected manufacturers. Mine Safety Appliances, has concluded the filter that works best on its equipment is Balston. The conclusion is much to MSA's credit and possibly is the kind of reason the company keeps the respect it enjoys, since MSA previously used in its instruments, filters the company itself designed. End users, the real test From the standpoint of end users of vehicle exhaust test equipmentthe auto companies themselves-the trend to Balston also is evident. The Vehicle Emissions Department at Chrysler Corp. uses analytical carts built by a Chrysler Instrument Division as well as some built by outside suppliers to test raw exhaust for N o s , propane gas, and carbon monoxide. In the process, the exhaust, which comes from the engine hot, is cooled in a coil before going into the analyzer. In cooling, however, moisture condenses and flows with the sample stream to sample cells where the readings are made. This moisture prevents accurate readings and can severely damage the instrumentation. Jack Lane, supervisor of the Methods and Procedures Group in the Emissions Department, said, "Blow-
ing out any accumulated water is a time-consuming process that was causing us a serious downtime problem. But, once we put in the Balston filters, we eliminated the problem." At another Detroit area plant, technicians conduct a wide range of emissions tests to produce data required by development engineers and federal and state agencies. One goal at this facility is minimum downtime of test equipment. The technicians here use chemiluminescent analyzers (CLAs) supplied by several manufacturers and, at one time, they all had two things in common: each came equipped with 7-cm paper filters, and each required too much service attention. I t didn't take the experienced instrument maintenance people long to pinpoint the trouble. The paper filters, designed to protect the CLAs, actually were fouling them. Particulate matter in the sample stream was punching holes in the filters and little bits of paper became entrained, clogging the instrumentation. Fortunately, the maintenance people had learned of Balston filters and tried them on the CLAs. The result was a remarkable decrease in downtime for these vital instruments. In another area, engineers perform a series of raw exhaust tests on engines and use diaphragm pumps to circulate samples to an array of test instruments. According to one engineer, pump failure caused by a pump valve clogging with particulate matter was a big maintenance problem. Once again, the engineers installed Balston filters and once again they solved this problem. "In general," the engineer said, "we have had considerable success using Balston filters in our emissions test instruments." At yet another emissions laboratory, engineers were experiencing problems on their constant volume
samplers (CVS). The CVS systems are back-pressure regulated systems; a critical element of each is a pressure regulator. Test engineers found that these regulators were failing too frequently as a result of particles in the sample lines. This was causing inaccurate test data to be generated and a great deal of costly lost test time. But when these engineers tested a Balston filter in the system, they found their regulator problem was solved. Similarly, when these same engineers encountered an instrument failure problem on their exhaust emissions bench analyzers, which sample raw exhaust for CO, Con, NOx and hydrocarbons, they turned to Balston filters to solve it. The filter effectively eliminated moisture and particulate matter from the sample stream, thereby providing the protection required for the instruments to produce reliable data. The value of these filters in emissions testing was, perhaps, best summarized by Ford Motor Co. which reported that at its Emissions Testing Laboratory (Dearborn, Mich.), "The application of Balston filters in the emissions analyzer train resulted in a significant reduction in equipment downtime. The filters have proved their worth by reducing the deteriorating effects of particulate and liquid contamination that interfere with the proper operation of analyzers, pumps, solenoids, and valves." Why it works The reason for the apparent trend toward Balston filters by instrument makers and users is, if you ask them, obvious; they simply work better. But the reason they work better may not be that obvious, although it is relatively simple. The heart of this filter is the filter tube which has '/B-in. thick walls Volume 8, Number 9, September 1974
791
DuPont source monitoring 1 . systems let YOU Dmve comdianc;! reliabb morith after month' after month after.
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Whether you need to monitor SO2 or NOXin your stack gas, Du Pont Instruments provides a source monitoring system that's complete from sample probe to readout and field proven in power plants, smelter operations, refineries, pulp mills and other manufacturing plants. All systems are designed with your needs and EPA guidelines and regulations in mind. All provide data acceptable to regulatory agencies. And all are built to give you years of dependable operation with minimal maintenance. Most systems have capability for multiple-point sampling with a single analyzer, resulting in significant cost savings for many installations. All employ the Du Pont UV-Visible Photometric Analyzer-proven in the field in over a thousand installations-as the basic detector. Systems are available for continuous monitoring of one pollutant, for sequential monitoring of pollutants, and for laboratory or survey use. If compliance with emission standards is your responsibility, Du Pont Instruments can help you. For full information on Du Pont Pollution Source Monitoring Systems, write Du Pont Instruments, Room 24004A, Wilmington, DE 19898.
CIRCLE 2 3 ON READER SERVICE CARD
792
Environmental Science & Technology
composed of glass fibers of a uniform diameter. Under a microscope, they would be seen as a random network of fibers. During the filtration process, fluid or gas passing through the fiber bed moves along a tortuous path, and suspended particles are retained when they contact the fiber. The retention mechanism is based on intermolecular (van der Waals) forces. Since particle retention is not a sieving action, the particles retained are much smaller than the spaces between the fibers. In gas filtration, such as in vehicle exhaust applications, particles smaller than 0.3 p exhibit a random (Brownian) motion superimposed on the directional motion of the gas flow. The Brownian motion greatly increases the chance of contact with and capture by the filter fibers. For particles larger than 0.3 p , collision of particles with the fibers as a result of inertial forces is effective for efficient capture. The two mechanisms of particle capture result in a minimum retention efficiency in gases at 0.3-0.6 p , with higher retention efficiencies for both larger and smaller particles. Balston produces several grades of filter tubes with the grade determined by the diameter of the fibers. Balston Grade D filter tubes, for example, which are most frequently used in automobile emission analyzer sample lines, have a filtration efficiency of 90% for 0.6-p particles, when measured by standard test methods for high efficiency filters (DOP Test and Sodium Flame Test). Finer Balston filters, such as the Grade B (99.95% efficiency) or Grade A (99.99+% efficiency), are sometimes used in particularly demanding sampling applications. Aside from superior filtration efficiency, original equipment manufacturers and users of analytical instruments have found other advantages in specifying Balston filters. For one thing, Balston offers a wide range of filter hardware in terms of sizes and materials of construction. The filter tubes themselves are disposable, so that when a filter must be changed, the hardware stays in place. And tubes are easy to install and seal since tubes are self-gasketing and don't require the use of rubber gaskets. With all this, Balston filters cost no more, and in most cases far less, than other currently available high efficiency filters. What all this evidence seems to indicate is that the analytical instrument field, particularly in the area of automobile exhaust emissions testing, has found a filter that provides a significant improvement in reliability and accuracy of test data.
