What Are Pros, Cons of Green Sand Iron Filters?
In my next to last article, I said I would next discuss regenerating green sand-type iron filters. So, let’s get to it.
It’s been a few years since I’ve done one of these, or even instructed a customer in how to do it. As I recall, this process was not a lot of fun. In fact, it was no fun at all.
The earliest green sand-type filters I sold were one-tank models. They had a multi-position, rotary-style valve to put the units through their various processes. This valve had a single handle that rotated 180 degrees or more to accomplish the regeneration. The regeneration process itself was strictly manual and started with — you guessed it — a reversal of the flow pattern to flush to drain the accumulated iron. The next step was to add the “not pleasant” potassium permanganate (PP) and let it slowly seep through the green sand. The final step was to flush the excess PP in the normal flow direction.
While all this was going on, the person doing the regenerating had to be pretty much standing by. As I recall, there was a prescribed time to do each of the three processes, so the person doing the regenerating had to have a good watch or perhaps a timer. To add the dreaded PP, the filter was depressurized and a large cap at the top was opened. This cap usually had an O-ring, and although it could be a leaker it hardly ever was. A measured amount of PP was then added to the tank. Of course to make room for this PP, the tank had to be drained slightly using a drain valve at its bottom. I remember that the PP could be added in solid form, but sometimes directions recommended mixing it in a small pail and adding as a solution. This mixing was really messy and if you got some PP or the PP solution on your hands or any other surface, it would stain badly.
The seeping of the PP solution through the mineral bed was also a timed item. Then the unit was flushed. Flushing continued until water coming out of the unit was clear. Pink water meant the unit needed further flushing. The handy bottom valve was a good place to check the appearance of the outlet water. The unit was then ready for service. But heaven forbid if the person doing the regeneration forgot to open the bypass valve. This would allow PP-laden water into the piping system.
The good news was that this regeneration did not have to be done as frequently as a water softener regeneration. If the owner was really diligent in doing these regenerations, these green sand units worked quite well. I had one customer who was a professional (a dentist) and he was very punctual about regenerating his unit. His worked very well for many years. The fact that his wife would have a royal fit if they had anything but iron-free water may have motivated him.
One downside to these green sand filters was that the backflow needed to be considerably faster than the service flow. In some homes, there was just not enough pump capacity to do an adequate back flush. Another major downside was that the mineral bed had a tendency to channel. That is, the water somehow found a way to get through a hole in the bed or at least use the same path all the time, making the bed very inefficient.
As you have probably figured out, doing this regeneration in a home setting in the busy, busy, busy days of 2019 would be an absolute no-no. In a commercial or industrial setting where a licensed plant operator was in charge of this process, it would work quite well. These single-tank green sand filters are, I believe, a thing of the past in domestic applications and I will say that is a very good thing.
Staying with the green sand as a media, some manufacturers later came out with semi-automatic iron filters. These were just like the single-tank units but with a reserve tank, or “brine” tank, if you will. This brine tank was sometimes nothing more than a good quality five-gallon bucket with a lid on it. The liquid level was manually controlled through the regeneration valve and, from time to time, the homeowner added some solid PP to make the “brine” effective.
Some of these units had a 1, 2, 3, 4 position manual valve, not unlike the early water softeners that had a lever like the gear shift on a car. However, the person doing the regeneration still had to keep track of the time of each cycle and the PP was still messy.
At one time you could buy potassium permanganate at some drug stores. Later, I believe you had to get it through the filter manufacturers. Safety precautions regarding the substance that I wrote about two columns back still applied.
I had one of these two-tank iron filters in my own home and, frankly, it never worked very well. I was quite disappointed with it. It was probably better than nothing, but not much. I think the nature of the green sand, the dreaded PP and the fact that most of these were manual or semi-manual combined to make these filters only semi-successful, at least in domestic settings. I will not comment on commercial or industrial uses, as I don’t think I ever sold one of those high-capacity units. Next time, I’ll write about some iron filters that came after the green sand models that were initially nothing special either, but eventually pretty darn good.
As I write this in the middle of May I have mowed my famous or infamous lawn three whole times, and it is looking very green and very good. To you folks in the South, you’re probably amazed at this statement. Our weather has generally been very cool, damp and windy with nighttime temperatures low enough to make our heat pump run at least for a while every night. If you still have to use potassium permanganate, you have my sympathy. If you don’t use it, be thankful.
For more John Schmitt columns, visit www.nationaldriller.com/schmitt.