Boiler Pump Dielectric

[Jim Robinson]

I was asked about the lack of a dielectric fitting or union on this boiler pump. I realized that most of them do not have them. I researched a little bit, and it does appear that they are not normally used on the circulation pump. Less oxygen in the water was one reason given. I couldn't find any mention of it in the boiler installation instructions or in the Taco pumps web site.

Does anyone have more information? Do you call out a lack of dielectric fittings on the boiler pumps or other connections?

[Jerry Peck]

That fitting looks like a cast fitting, brass or bronze, maybe cast copper (which may be almost equivalent to brass on the cathodic scale?).

Brass and bronze are considered to serve as a suitable for use between copper and steel.

[Bob Harper]

Naw, just looks like a std copper male adapter. Note the coupling above it. It probably leaked after changing the pump out and our hero tried to sweat the joint again with too small a tip. If you try sweating this joint with the pump flange attached and a small torch, it is very hard to get it hot enough for a good joint. The best way to fix it is to cut the pipe, unscrew the adapter and clean everything up, clean and sweath the joint btw the pipe and the adapter, cool, dope/ tape, re-assemble threaded joint in flange, prep coupling and pipe, re-assemble pump loosely in place and sweat coupling, cool, tighten flange bolts then leak test.

Crud looks to be flux corrosion.

With an air vent, oxygen in the closed system should not be a problem. Dope and tape should be enough btw copper threads and flange.

[Jerry Peck]

Naw, just looks like a std copper male adapter. Note the coupling above it.

I'm not referring to that standard male adapter, I am referring to the piece that male adapter is screwed into ... that piece which is bolted to the top of the pump flange - that piece looks to be cast brass.

Admittedly, the point of the arrow is to the top of that piece and is almost pointing at the male adapter.

[Bob Harper]

yeah, Jerry, I think that's just a bushing. Look at the diameter of the flange compared to the male adapter. They sell various diameter flanges but often guys just use a bushing instead. Bushings are prone to leaks due to insufficient metal between the thread roots making them prone to cracking, which is why they aren't allowed by the gas codes.

[Jerry Peck]

yeah, Jerry, I think that's just a bushing. Look at the diameter of the flange compared to the male adapter. They sell various diameter flanges but often guys just use a bushing instead. Bushings are prone to leaks due to insufficient metal between the thread roots making them prone to cracking, which is why they aren't allowed by the gas codes.

Bob,

The piece I outlined in red is the male adapter and is screwed down into the mating flange, which I have outlined in blue. (The dashed red is indicating the male adapter part which is screwed down into the mating flange.)

I am referring to the mating flange as looking like cast brass.

Copper to brass is okay, brass to steel (the pump housing) is okay.

No dielectric fitting required as the brass mating flange (if it is brass) serves that purpose.

[David Bell]

All the circ flanges I have seen are steel unless used for potable water then a bronze pump is also used. A Taco 007 circ has a cast iron body.

[Jerry Peck]

All the circ flanges I have seen are steel unless used for potable water then a bronze pump is also used. A Taco 007 circ has a cast iron body.

Look at the different styles of flanges along the bottom of this page, and the different materials those flanges are made of: Circulator Pumps Reviews | Grundfos & Taco pumps (http://www.circulator-pumps.com/)

Several of them sure do look like cast bronze or brass to me.

[Terry Sandmeier]

Most all of these pump flanges are brass, this one does not look any different. On the circulator there is an rubber flat O-ring between the circulator and flange, this makes the tight seal. The threaded male adapter do leak some times when a installer uses thread tape and/or pipe dope and then sweats on the pipe to the male adapter. The correct fix is to unbolt the flange and circ. and unscrew the adapter and re apply tape and/or dope and re tighten. There is no need for dielectric unions in this application.