Rust Clogging Return Valves & Pumps

Paullessard

Folks: We have a 120 year old 1-pipe steam heat system that dumps a lot of rust into the return pump that sits about 24 inches below the boiler. The pump has to be replaced almost every year as the valves become clogged. Other valves near the boiler become clogged as well. We drain water from the boiler weekly to get out the rust, but, of course, the rust has already passed by the critical valves at that point. We have replaced all the air valves and leaky inlet control valves on all the radiators. We have insulated steam pipes throughout the building. How do we stop the rusting? How do we save money? We can bear the fairly high cost of heating but the surprise valve and pump repairs each year are stressing us.

Jamie Hall

Draining water from the boiler weekly is only going to make the problem worse. There are no real general rules for this -- but I would be concerned if a residential boiler needed more than a gallon of water per week. The problem is that the new water carries oxygen, which is what causes the rust (no oxygen, no rust).

There are a few chemical treatments which reduce the potential for corrosion somewhat -- but only a few.

Are you adding much water to the boiler in the course of normal operation? If so, you should redouble your efforts to find the leaks -- probably steam, but also quite possibly leaky returns -- and fix them. That much rust suggests rather strongly that the wet returns may not be in the best of shape...

MilanD

Did you try strainers? Not sure if it's possible to install them somewhere before the pump.

Also, check pH level. From what I've been reading, you need pH to be 9.5 to 10 to get the slowing down of rusting. With all the fresh water, your pH is probably around 7. Lye (sodium hydroxide) can get pH higher, or you can try soda ash, like for pH control in pools. You need to test it though, to not overshoot on either. Too high pH and you get frothing and wet steam. Too much soda ash, you get excess HO3 which also increases rusting, vs. lye which creates HO, much less corrosive.

Then, there are oxygen scavengers you can try, namely Sodium Sulfite. Sulfite, not sulfate.

When you get it cleaned up and under control, try steamaster tablets or 8-way to keep the pH and water quality in check.

Btw, all the above you can get on amazon. Get also pH tester or litmus paper, tds tester, and chloride tester. Hanna Instruments has the chemical test kit for chlorides, electronic ones that go above 20 ppm are very expensive. The rest is available quite economically on amazon.

PH 9.5, tds as low as possible (distilled water, ion exchange or RO water will have 0-3 range and both will need lye or soda ash to raise pH), plus o2 scavanger.

For what you are saying, you may try to also get a condensate return tank installed in front of the pump. The off the shelf ones do have an inch or two of dead space at the bottom above the flange for mounting the pump. This 2 inches will deposit any debris before pump gets it and can be drained out from time to time. Or if you have access to a good metal shop, they can make you a tank with 2 inch drop before the flange and a few drain ports.

Jamie is right: all that new water adds a lot of more oxygen, and probably a lot of solids (Ca, Mg, Na) which will also speed up failure on the boiler itself.

So when you get the physical barriers set up, and water pH and O2 under control, you will need to test and get your water quality in order with filtration of make up water carbon and RO filter, or Carbon and ion exchange filter...

Hope this helps.

MilanD

Btw, if this has been going on for a while, wet returns need to be cleaned very very well, along the above measures. You want to flush all the loose rust away. Most of it is, likely, coming from wet returns.

JUGHNE

Strainers with blow down valve attached where the clean out plug is. You can blow them down as needed.

Even a drip leg before strainer with blow down valve may catch a lot and not plug the strainer so quickly.

Is it possible to change the wet return piping or is it under a floor. As stated above the wet return pipe are the source of the rust and may be close to leaking if not already doing so.