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www.fueloilnews.com | FUEL OIL NEWS | NOVEMBER 2014 41 HVAC/ HydroniCs up into a radiator. In particular, a horizontal pipe feeding a radiator should have a gate or full-port ball valve, never a globe or stop valve. By its very construction, the latter types will back water up in the radiator. Some improper valves can be found that were original to the installation, so even back then you couldn't fix stupid. The best solution is to equip these radiators with some sort of limiting air vent. Thermostatic radiator valves, Figure 2, which replace the usual one-pipe radiator air vents work well. They should include a built-in vacuum breaker and are not the cheapest option since one is required at each radiator. These vents should not be used in the area where the room thermostat is. This area must always reflect the true, actual heat in the system in order to operate the thermostat. One solution is the adjustable air vent. Frank likes the Vent-Rite #1, Figure 3, (which I also like), but I have used a lot of Hoffman #1A, Figure 4, by customer preference. They are both adjustable which allows the user to regulate the air venting rate. It can also keep air from leaving the radiator when turned all the way down. If the air can't get out, the steam can't get in, so you can keep the radiator from heating while leaving the shutoff valve fully open. That way if some steam does show up, it can condense and return quickly. I truly believe that main and radiator vents are some of the most important controls on a steam job. I include them even in the steam portion of my wiring classes, for that reason. Vacuum-type air Vents These were used on both one-pipe and two-pipe systems. They worked great with coal firing, since the system would go into vacuum as the coal pile burned down and keep generat- ing steam at lower temperatures. But with the much shorter firing cycles of oil and gas boilers, they can fail to open when they should, which can hold water up in the system. If water is held up and can't get back to the boiler the low-water cutoff may call for water from the feeder and here we go again into a flooded boiler situation. When the water is finally released, the boiler will flood. Check each radiator vent (if used) and each main vent. Replace any vacuum vents you find. Size the valves using the Gill-Pajek charts we mentioned earlier. Boiler piping and controls On larger boilers, the low-water cutoffs and/or feed pump controllers are normally mounted on piping next to the boiler rather than on the boiler itself. Regretfully, many are improperly installed by being mounted too high, which brings the water line too close to the steam outlets. This can cause the steam to drag water along with it (saturated steam), which not only can cause banging and slow or uneven heat- ing but also can result in a call for feed water. Improper near-boiler piping can do this too, if it's too small, not high enough or otherwise mis-configured. On most boilers, the water gauge glass should not be more than two-thirds full, but you should always check with the boiler manufacturer to be sure. On a pumped-return system, a boiler-feed pump controller such as the McDonnell & Miller #150, Figure 5, might fill the boiler to this point with- Figure 2 Figure 3 Figure 4 Figure 5