At the risk of beating a dead horse, I'd like to make another pitch for preventive maintenance. It's the most sensible, cost-effective way of keeping our equipment operating productively, efficiently and cleanly. Many people have taken this message to heart; many others, though, continue promising to “get around to it,” but other tasks intervene.
For those of you would like to set up a PM program for your burner and control systems, but are put off by the prospect of assembling it from scratch, here's your Starter Kit. In this column, I'll give you a shopping list of the diagnostic equipment you'll need. Next time, I'll look at the things to check and how often to check them.
Pressure and Velocity Measurement. Most pressures and pressure drops in combustion air and gas systems are less than 1.5 psig. Use a manometer capable of reading up to 36 to 48 inches water column (" w.c.), with a minimum resolution of 0.1" w.c. Liquid-filled U-tube manometers have long been the standard -- they're easy to use and nearly foolproof. However, they can be a bit cumbersome to use in close quarters. Electronic manometers are compact and handy to use, and their digital readouts eliminate guesswork in interpreting readings. It's a good idea, however, to keep a liquid manometer back in the maintenance shop to use as a calibration standard for the electronic unit.
If you have to read low pressures, say, less than 1" w.c., or measure velocities in air ducts and stacks, you'll need a second manometer able to read out in increments of hundredths of an inch water column. Your best bet is an inclined manometer, also known as a draft gauge or slope gauge. This is essentially a U-tube manometer, but with one leg of the tube set nearly horizontal. Thanks to the wonders of trigonometry, this stretches out the liquid column over a greater length and makes it possible to read pressures accurately at resolutions of 0.01" w.c.
If you plan to use this manometer to read duct velocities, you'll also need to invest in a pitot-static tube. This tube is inserted into the duct to collect pressure readings, which then can be converted to velocities.
For pressures exceeding 1 or 2 psig, a dial gauge will usually suffice, but be careful. Make sure you get a gauge with decent accuracy to start with, and then treat it kindly. These gauges can easily go out of calibration if they're subjected to excessive pressure or handling abuse.
Finally, don't overlook the small stuff -- the hoses, hose barbs and petcocks needed to hook your pressure-measuring equipment to the taps on the system. Buy more than you think you need and check your supply periodically -- petcocks, in particular, have a habit of disappearing.
Flame Signals and Electrical Readings. A good multipurpose electrical test meter, able to read AC line voltage, up to 20 mA DC and 50 V DC, will handle control and safety component readings, temperature controller and most flame detector outputs. Some older models of flame relays and controllers require a special milliammeter. For checking the current draw of fan motors and other large electrical equipment, a clamp-on ammeter will usually do the trick.
Temperature Readings. If you run your own checks on temperature-measuring elements, get a handheld digital pyrometer calibrated for the sensors you normally use. Cross-check its readings against your process temperature controller. In a pinch, you can do it with a multimeter that reads up to 100 mV for checking thermocouples and up to 10 V for RTDs and thermistors. However, you'll need calibration charts to convert your readings to degrees.
If you need to check heating and cooling temperature profiles within your ovens, there are a number of traveling dataloggers available. If it's not something you normally do, renting, rather than purchasing, a unit may make more sense.
If temperature losses off the outside skin of ovens are a concern, there are gun-type infrared temperature sensors. Point to a spot on the oven, pull the trigger and get a reading. They're also useful for shooting actual product temperatures inside ovens. If you're really serious about wall losses, a thermal imaging system may be in order. If the price turns you off, rental units are available, and in many areas, there are service contractors who will run a temperature survey for you.
Flue Gas Analyzer. This one depends. Analyzers are valuable diagnostic tools, and I don't hesitate to recommend them where combustion systems operate reasonably close to correct air/gas ratio (including secondary or makeup air). So, if you have a boiler, thermal fluid heater or any other system that is supposed to operate with, say, 10 percent or less excess oxygen in the exhaust, a flue gas analyzer is a wise investment. But, if you have an oven or dryer operating at 400 to 500oF (204 to 260oC) or lower, you're in the range where exhaust O2 readings are not especially sensitive to changes in air/gas ratio. Consequently, analyzers aren't a great deal of help in fine-tuning burner settings.
OK -- go fill your toolbox and come back next month. (Go to "The Second Ounce of Prevention.") Then I'll tell you how to put all this great equipment to use.