Munchkin boiler, Why did this work ?

[Tom Robinson]

I'm replacing a 20 year old Munchkin boiler that reportedly functioned well. I appears that the primary circulation pump from day one was installed backwards. Also the air separator / expansion tank is low and on the primary loop as opposed to secondary loop ... most design drawings have the separator and expansion on secondary loop? Weil-McLain manual also states the pump MUST be on the return line so as to avoid cavitation while sucking from supply? Reverse pump and leave it alone ? It worked for 21 years.

 

[Fitter30]

Try taking a pics of the side of the pumps thats where the arrow is for direction of flow. Normally grundfos pump label on motor top of label is discharge.

 

[Sponsor]

 

[Tom Robinson]

I made note on picture that suction was identified. I've been a domestic pump service tec for forty years, simple enough to see by casting shape alone where water is diverted into center of impeller.
I just find it fascinating that the primary loop mixed the cold backwards and worked well enough to not create problems.. I've been a domestic c-16 pump contractor for 40 years so the friction / head / cavitation thing is no mystery. The thermal dynamics and air extraction that I don't routinely deal with.

 

[Fitter30]

Expansion tank on discharge of the pump would do anything for expansion the air separator wouldn't work to it design. Flow through the boiler backwards would cut the design temperature rise by half. Secondary loop tees backwards can't see how it heated unless theres more heat emitters than design. Read this article.
https://www.pmmag.com/articles/93285-pumping-away-from-what

 

[Tom Robinson]

thank you so much ... I love learning , excellent article !

 

[Fitter30]

Never seen a zone valve manifold made with that style of valve. Does it have a brand and model?

 

[Tom Robinson]

all Wirsbo