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Air Purge Index

Tracking the Valve You Can't Find in the Store

We frequently hear of the mysterious ‘automatic fill valve.’ Like the ubiquitous ‘nucular’ weapons we heard about for half a century, they are difficult to find. Of course, looking through our dictionaries, we could eventually come across misspellings like ‘nuclear.’; but that couldn’t be right because the TV commentators, and even Presidents, always referred to ‘nucular weapons.’

If we look up references to ‘automatic fill valves’, we come across devices to fill horse troughs, baptismal pools, humidifier pan floats, and toiler tank fills; but we get so little help with that valve referred to by helpful handymen and plumbers that is supposed to be attached to a hot water heating system.

If we go to a plumbing supplier and ask for an ‘automatic fill valve,’ we get questions about what we want to fill, or the knowing wholesaler gives us a pressure reducing valve. He might even insist that the device is called an automatic fill valve, even though the catalogue always names it a pressure reducing valve.

This insistence can not be right, because all a pressure reducing valve does is feed water into a hot water system while you are supervising the fill procedure after repairing the system. Most manufacturers tell you in their instructions to close the hand valve before the pressure reducing valve when you are done to prevent damage from a catastrophic line break. So how can a valve that is shut automatically feed water into a system to make up for leaks you left in the system?

Obviously, if there are no leaks in the system, there is no need to fill it. I can remember when the only circulators that were available had shaft seals that would leak after some years. Leaving a valve that could drip water out of a sand hole or cracked fitting for years until the seal went bad made no sense. This arrangement seems more properly named an ‘automatic flood system.’

I often hear about replacing a pressure reducing valve screen or the whole valve because it is clogged with dirt. I can’t imagine the amount of water that had to flow through the valve to fill the screen with mud. Perhaps the hand valve that was supposed to be shut was leaking by to feed the heating system as it was running water down the foundation blocks for years through a leak.

Imagine how many boilers and circulators were replaced in that system due to oxygen corrosion and liming from fresh water running through the system constantly. That is why boiler manufacturers and their accessory companies that make pressure reducing valves recommend shutting off the hand valve to isolate the hot water system from the fresh water supply.

If I would put any kind of automatic control on a boiler it wouldn’t be one that guarantees corrosion and scaling. I would install a low water cutoff to prevent the boiler from damage after water leaked out of a system. Some think that is too excessive and expensive. After all, before a boiler with radiation above it burns up, the first clue of a leak is bubble noise in the top radiation, a bit more time and the top floor doesn’t heat, then if not fixed the boiler starts making loud clunking noises. Eventually, the cold and din gets the homeowner to call a repair company. At least, a pressure switch on the return set at 10 psig would cut off the burner.

But, I am straying from the search for that mysterious device. I know that steam systems have boiler water level controls available. Most residential steam systems still require the homeowner to hand-fill the boiler while watching the sight glass. They sometimes get an automatic water level control. If the control fails open, then they have an automatic fill control evidenced by the water shooting from the upstairs vents.

But there doesn’t seem to be an automatic fill valve available for hot water systems in my world. I am not sure how they are to work. Do they have a sensor at the top of the system to know when water is up to the top? Do they have a safety shutoff that monitors flow after the system is filled? When you come across one, let me know. Hmmm, perhaps there is an opportunity for a needed invention here!