Pumps in series

Mark J Strawcutter

Classic setup with 4-way valve to create pseudo pirmary/secondary configuration. One circ on boiler loop, another on system loop.

With valve at one extreme (low load) the boiler and system loops are decoupled. Circs operating independently. No problem.

With valve at other extreme (design conditions?) you effectvely have one big loop but the circs are in series with each other. What potential problems can this cause and how can they be avoided?

Mark

Terry

np

2 Pumps in parrellel will double flow w/o affecting head. In series the head is doubled and flow in not affected.

I would assume that this 4 way has a motor on it and is controlled via floating action controller. Which would mean that even under "design" conditions, the valve would infrequently see "full open" position (the secondary would overshoot temperature & the controller would mod the 4way closed.

It would probably see 0-80% open 95% of the time.

Terry.

DanHolohan

The only potential

problem I can see would be if there were TRVs that had a low rating for the maximum pressure differential. Not likely on most of the stuff we discuss here, though.

hydronicsmike

Primary/Secondary

Have a look at the Pic. I hope this helps.

Regards,

Mike

JimGPE_3

Just for the record

so someone doesn't try this (this comment is only slightly revant to the topic), if a pump in a piping system handles x flow, adding to the SAME PIPING SYSTEM another identical pump in parallel will not result in 2x flow.

I know it is picky, and probably everyone else reading this knows this twice as well as I do but this is an educational site, and I add this for accuracy.

Sorry for the interruption.

Now back to your regularly scheduled thread....

Floyd

I wish.....

That you would clear some of the up more in detail....
Maybe we do need an engineer here for somethings.....:-)

What does it give you if you parellel pumps and.....
how a bout stacking two pumps.....
does it really double the head?????

Are there some real #'s avaiable?????

Reason for asking is that I am working on a project right now that could use
about 15 GPM @ 50 ft head......
one pump to do that would be rather large, and expensive,
two smaller pumps may be the anwser.....

Just wondering......

Thanks!!!

Floyd

Mark J Strawcutter

Will that still provide

boiler protection from low temp return?

Mark

Jamie Hall

an engineer (sometimes...)

You have to look at the pump curve(s) vs. the system curve. If you have two pumps in parallel, they will both operate at the same head (assuming all the piping is symmetrical!) -- whatever that may be. The head is determined by the flow through the remainder of the system and the resistance to flow in the system. You need to plot the head vs. the flow in the system and superimpose on that the curve of the sum of the flows from the pump(s) at a given head -- where the two lines cross is where the system will operate (clear as mud!) (note that two pumps in parallel don't have to be the same, although some interesting problems can arise if they are significantly different). You can do the same kind of thing with two pumps in series -- plot the system head vs. flow curve, and superimpose on it a curve of the sum of the pump heads at a given flow.

I have never been enthusiastic about two pumps in series, though, as you can get quite serious flow pulsations and instabilities, depending on details of piping and valving...

hope this helps

j

hydronicsmike

Certainly, IF...

...motorized and operated by a Mixing Control with Boiler Return Protection Feature.

I hope this helps.

Mike

Mark J Strawcutter

I think I see

The more the 4-way throttles back to direct more "boiler supply" back to the return, the less flow there is between the 4-way and the pri/sec Ts but the more there will be across the common piping (between the real boiler supply and return). Net effect is warmer return water.

You would just need to be sure to locate the boiler return sensor for the 4-way control back between the boiler and pri/sec Ts - if you put it between the Ts and the 4-way it wouldn't work.

Sound right?

Mark

JimGPE_3

Well said, Jamie!!!!

Jerry Boulanger

If you have two pumps in parallel

you will be able to get about 70-75% of the total flow by running one pump, e.g. 2 pumps x 10 gpm each, one pump will produce about 15 gpm. For pumps in series, since the same flow must go through both pumps it is always best to use identical pumps. When installing pumps in parallel, split the flow evenly by running it into the bull of a tee so both pumps get the same flow.