Odd pumping question (ME)

[Deleted User]

I know, you're never supposed to have two pumps of differing head/GPM capacities in series, and as pro, I would never do it, however, we came across a snow/ice melt system in a car wash where someone had done this very thing.

In the case of a small pump pumping into a larger pump at atmospheric conditions, I know what happens. We do this all the time when we're filling systems with aunty freeze. My question has to do with closed loop systems.

If, say a person has a Gfos 4075 in series with a Gfos 1542, what is the end result?

Now, flip them, the 1542 is pumping into a 4075, what is the net result?

Rich Corocran? Joe Matiello Any one care to comment?

TIA

ME

thp_8

Simply

Depending on the placement of the smaller circ. It is going to be restriction on the suction or a restriction on the supply.

Joe Mattiello

It's OK

You can use dissimilar head pumps in series, with no detriment to the lead pump, or degradation of performance. Let’s not forget that water will flow through a centrifugal pump, running or not running, not like a positive displacement pump that displaces a certain amount of flow per revolution. If close couple the pumps, it is important to have them pumping away from the expansion tank to avoid Cavitation. However, you can put the pumps several feet away from each other as a push/pull arrangement distributing the head pressure generated more evenly. Occasionally I have advocated a 007 in front of a 0011 in a wood boiler application to help satisfy the NPSH of the 0011 with good results.


Taco, Inc.
Joe Mattiello
Technical Service Technician
joemat@taco-hvac.com
401-942-8000 X 484
www.taco-hvac.com

Rich Corcoran_25

No problem

You can install the pumps as you describe.

RC

[Deleted User]

Thanks for the response guys, still wondering...

what would the end result be. I realize you'd need a specific example, so here goes.

500' circuits of 1/2" PEX, 3 of those in parallel, fluid parameters = 40% solution of prop glycol, max temp = 140 F. Based on a required flow rate of 2 GPM per, then I'd need approximately 6 GPM, I'll let you calculate the head, and tell me where it would ACTUALLY be based on my previous expamples using the two different Gfos pumps.

If, for the sake of conversation, the pressure drop requirements comes out to X feet of head, would the actual GPM be the addition of the two pumps GPM capacity at that X foot of head capacity? Or is it like pumps in seris and parallel, "Approximately double...?"

BTW, the above scenario is for real...

Thanks guys, and FWIW, I learned something new today. Help me finish learning so I can apply what I've learned and teach it to others.

You're NEVER too old to learn. And as my pappy used to say (reat his soul) "If'n you don't learn something new every day, you were either (A., Gone fishin', or (B Not payin' attention. And if you WERE (A. gone fishin', and you didn't learn something new, you WEREN'T (B. paying attention!"

ME

thp_8

That's if

the net discharge gpm of the 007 is greater than the net discharge gpm of the 011. Most of these wood heater set-ups and I will use that term loosely, are lucky if they are moving 8 gpm with all the 1" pex and being a mile from the house. With that in mind we are running PSC motors here and lets just say that we are running 8gpm with no or little head pressure on the 007 because the 011 is taking it up. This will put the 007 under it's performance curve. The motor heat has to go somewhere. In to the windings we will go. Early motor failure will result.

Brian (Tankless)

THP is right

a motor must "work" to be efficient. If it's under-utilised, heat will build up in it, it has nowhere to go. The smaller motor is "along for the ride" & is/will drag the bigger motor "down".

The smaller pump WILL fail due to heat problems. It's a voltage/current phase angle thing

Take the small pump out, because sooner or later, the bigger motor will fail.

Trust me, I know motors.

Time for a brewski, and check to make sure the flicks & tea's haven't carried my radiantly-heated dog away.

Brian, in Tick-land.

thp_8

No Flow

The above scenario using the circulators listed will provide no flow. You need 71.5 ft. H20 to pull that off. Thats 31.5 psi to obtain the flow required.

Constantin

Thanks for the interesting point...

... as usual, it makes sense. More importantly, any word yet on the job situation? I'm squeezing a thumb for you (as we say in Germany when we wish someone luck).

Jerry Boulanger_2

Pumps in series

For pumps in series, the flow through each pump must be the same. Since pumps must run on their curve, each pump will develop a differential that corresponds to where the flow rate puts it on its curve. It is easy to plot a curve for any two pumps in series. For example, if pump 1 will move 5 gpm at 10' of head and pump 2 will move 5 gpm at 7' of head, the curve for the two in series will be 5 gpm at 17'. The little spreadsheet attached will do it for you - it is currently plotting for a B&G NRF22 in series with a NRF33. Put in new flow and head values for any two pumps and it will plot them. You can then get an idea of what the pumps will do together.

Brian (Tankless)

Thanks, Constantin

The job situation is looking up.

For a better understanding of how to improve power factor & make motors run better, check out www.energysmart.com

I "treated" a freind's entire home with PowerPlanners from this company and lowered his KW usage by almost 40%, and have the utilty bills to prove it.

Basically, they "read" the mind of the motor, and modulate the voltage to match the load at the time, bringing voltage & current down, raising PF, as well as lowering temp's & vibration.

In almost 40 yr's as a maint' electrician, I can confidently say that over 90% of motors I've worked on have been oversized. Once the voltage is matched to the load, electrical vibration almost disappears and motor temp's drop.

I worked for PPG, where they spent enormous amounts of money to lower machinery vibration. But the vibration they were looking for wasn't mechanical in origin, it was electrical.

After I left there and went back to show them what I found, they refused to believe what I demonstrated for them. Instead, they spent more money on more fancy power quality instruments to prove me wrong, but they proved me right. All their motors are oversized, they vibrate & overheat, but have not bought a single PowerPlanner yet. BTW, I used a Fluke 43B, the best PQ analyser money can buy.

I have had more problems with "Engineer Ego" than I've had with equipment, (present company not included in that statement .

Must get busy.

Later, fella's