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Pump basics, in series

Timco
Timco Member Posts: 3,040
Howdy to The Wall. It’s been quite a while since I’ve posted or been around, lots going on these days.

So I have an irrigation system where the pumps in the shed pull from a 1000 gal above ground cistern behind the shed. There are two pumps in series, and I’m fairly certain they are close in performance. The well pump only refills the cistern wide open in increments to not deplete the well. If pumps are in series, having two only helps overcome friction loss through the filter and piping friction, correct? I get excellent pressure and performance out of my zones. One is an older B&G that I salvaged many years ago and now seems to have a leak. The other is a newer 3/4 HP from Lowes. If I’m pulling from a tank that’s above the pumps through one string filter, is there even a need for two pumps? Is that making life easier on the second pump? One is pre filter and one is after the filter. There is also a large well tank on the system to keep the pressure smoother and less bouncy. Should that ideally be upstream or downstream from the pump(s)? Thanks for your input.
Just a guy running some pipes.

Comments

  • hot_rod
    hot_rod Member Posts: 21,853
    Is the b&g s hydronic circulator? 
    Or an irrigation pump?
    If you have model numbers look for the pump curves go see how they match
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • HomerJSmith
    HomerJSmith Member Posts: 2,393
    edited August 2023
    Well, with the cistern above the pumps you don't have to worry about NPSH (Net Positive Suction Head).
    If pumps are in series, having two only helps overcome friction loss through the filter and piping friction, correct?
    Yes, at a given flow.
    If I’m pulling from a tank that’s above the pumps through one string filter, is there even a need for two pumps?
    It depends upon the desired flow rate at your pressure loss thru the filter and piping. If you had pressure gauges on your sys, it would give you an idea whether you need one or two pumps. Pumps have a pump curve that tell what the head of the pump is at a given flow. You can look that up.
    There is also a large well tank on the system to keep the pressure smoother and less bouncy. Should that ideally be upstream or downstream from the pump(s)?
    You are going to pump into your well tank. You can't rely upon the head of the cistern to fill it.
    Is that a bladder well tank? What bladder pressure?
  • jumper
    jumper Member Posts: 2,208
    Unless one really knows what she is doing then pumps in series can be tricky. Sometimes there can be insufficient NPSH even with atmospheric pressure plus additional height above the pump.

    You have to determine or at least guesstimate what flow you want and how much pressure you need to achieve that flow. A correctly chosen pump will save electricity and will not destroy itself so soon.
  • leonz
    leonz Member Posts: 1,051
    edited August 2023
    Timco said:



    Howdy to The Wall. It’s been quite a while since I’ve posted or been around, lots going on these days.

    So, I have an irrigation system where the pumps in the shed pull from a 1000 gal above ground cistern behind the shed.

    There are two pumps in series, and I’m fairly certain they are close in performance. The well pump only refills the cistern wide open in increments to not deplete the well.

    If pumps are in series, having two only helps overcome friction loss through the filter and piping friction, correct?

    I get excellent pressure and performance out of my zones.

    One is an older B&G that I salvaged many years ago and now seems to have a leak.

    The other is a newer 3/4 HP from Lowes. If I’m pulling from a tank that’s above the pumps through one string filter, is there even a need for two pumps?

    Is that making life easier on the second pump? One is pre filter and one is after the filter.

    There is also a large well tank on the system to keep the pressure smoother and less bouncy.

    Should that ideally be upstream or downstream from the pump(s)? Thanks for your input.

    =================================================================

    What type of irrigation system do you use, drip, impulse, ocillating, soaker??

    Are you using garden hose or black PVC pipe?

    Is the pressure switch for the irrigation feeder pipe set at 20 low/40 high to shut off????

    The last thing you want or need for your system is two pumps for a small diameter irrigation water piping.

    Is the pump from lowes a shallow well submersible pump, jet pump with one suction strainer or a 2 pipe jet pump or a primed centrifugal with a foot valve?

    What type of pump is it?, and what brand it is it?

    Ideally you should be using only a 2 pipe jet pump for a pressure pump from the cistern to the pressure tank and simply employ a high quality timer to control the water flow time.
  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    All of the above. To add a bit more, unless the two pumps are matched, one will be operating at a different pressure difference than the other, although the flow through both will, of course, be the same. It is even possible, depending on the pumps, that one of them is adding essentially nothing at all -- just using electricity needlessly (in an extreme, one pump may actually be driving the other as a turbine, thereby guzzling even more power). You would need a pressure gauge before and after each pump to determine what they are doing.

    In general, if you can find one pump which produces adequate pressure at the required flow rate you will be much better off. In a situation with a filter, such as you have, the pump should be before the filter, not after it, as the head loss through the filter (especially towards the end of a run) may cause the pump to cavitate, which will destroy it remarkably quickly.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 21,853
    You should start with how many gpm you need and what psi you want

    watch the classified for a true irrigation pump. I picked up a Mupro 2 hp cast for 300 bucks recently. It will power a 2” fire hose and blast about 60’ with a fire nozzle on it

    sell the two you have and select the correct single pump is my advice also if you need more  flow or psi. Red Jacket and Goulds are other common cast irrigation pumps

    I got 1 year our of Harbor  Freight 1 hp irrigation pump before the bearings went out. Buy a good lifetime pump
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,233
    Hi Timco, It has been a while! Anyway, I just wanted to welcome you back... You're getting good advice and good questions. ;)

    Yours, Larry
  • HomerJSmith
    HomerJSmith Member Posts: 2,393
    I like spin-down filters. A spun filter is looking for smaller contaminants which may increase the pressure loss and the filters aren't free.