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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I do multifamily apt complexes with a central hot water system These

Customer Question

I do multifamily apt complexes with a central hot water system
These systems B&G 2 and 3 HP pumps
The next to the last building I done the B&G pump had a 2- bolt flange threaded 1-1/2 The incoming water was 3" inch. I reduced the 3" to 1-1/2 and installed a 1-1/2 ball valve and then connected the pump.
The outlet was the reverse of the inlet.
The engineer of record said it looked good and signed off.
Now another phase of this apt complex came up and I prefabricated the
set up and installed a 1-1/2 jumper so when the pumps arrived it would be an easy install.
Well guess what the new pumps had a 4 bolt flange and a 2" threaded inlet and outlet.
I called my supplier in a panic because I prefabed a 1-1/2 setup as before and told him the situation, he said use a 2x1-1/2 bell reducer.
I did that and the same engineering firm different employee went nuts on me
Turned the installation down and said 3" ball valves had to used and 3" pipe right up to the pump.
My question is, is the 2nd installation wrong?
Submitted: 1 year ago.
Category: HVAC
Expert:  Gaztech replied 1 year ago.
I agree a 100% with the second opinion.A 3 inch pipe was installed in accordance to pipe sizing chart calculation, reducing in this case before the pump is not a option.
Customer: replied 1 year ago.
Your not answering my question
Is reducing the pump flange from 2 inch to 1-1/2 wrong and if it is why?
Expert:  Rick replied 1 year ago.
It seems my colleague has opted out. I hate to be the bearer of bad news (please don't shoot the messenger). I sort of agree with the second engineer. Reducing the pipe size before you get to the pump restricts the flow and going from 3" to 1 1/2" is a drastic reduction. This will cause the water flowing through the 1 1/2" to speed up considerably and could also cause the pump to cavitate due to inadequate flow. Reducing the pipe size right at the pump is not as significant because there is going to be some size restriction through the volute anyway unless you have a really big pump. System heating capacity is how pipe size is calculated. Also system flow and pump head is calculated in relation to the pipe size.

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