Double Water Pumps Question

[SLOBuds]

I have 10 acres that I installed irrigation pipe on a few years back. This is a well system and has a pump with a bladder pressure tank to provide pressurized water through the parcel.

I am thinking about, or rather questioning, about putting a second pump/pressure tank on an opposite side of the property. The idea is to provide a secondary backup system for water pressure, and maybe to even out the pressure during heavy usage.

My well supply guys tell me that I shouldn't install a 2nd pump like that. They tell me that the 2 systems would 'fight' each other. But I don't see how that would happen - the fighting part.

Say one pump is set to go on at 50 lbs/off 70 lbs, and the other is set at 40lbs/60lbs. I think that the 50/70 will cycle most of the time unless there is heavy usage bringing pressure down below 40. Then the 40/60 would kick in. Both would run until pressure exceeds 60. Then the 40/60 turns off. Above 70 the 50/70 turns off.

So basically, the 50/70 does most of the work. If one fails, the other kicks in though.

Am I missing something here? Any other ideas on providing a redundant system?

Thanks

 

[Sackett2]

You are right about the pump action, we ran a similar system on the fire system at my ICBM Missile site. However, both bumps had there own lines into the water tank.
Now, (and I'm not a expert by far-just throwing things around) I wonder about the "draw" of the pumps. Can the well support increased water draw? Is there room for two pumps, I'm assuming they are above ground. How about a increased volume submersible pump.

 

[MikeD74T]

The fighting can occur when the demand pressure is just below the start setpoint of the second pump. With the first pump running & demand keeping the system pressure just below the second start setpoint, the second pump start can boost pressure quick enough to shut it's self off & pressure will immediately drop back below the start point of the second pump. This is short cycling.

You can work this out by balancing the pump sizes, demand rates, & setpoints but that could be a lot of work - especially if the pumps are 1000' mile apart. You might be able to control demand better by putting a couple of check valves somewhere in the system & setting both pumps the same start/stop. This would work best if a check valve was each side of the largest single demand. i.e. Both pumps could feed the largest demand but not back feed to the rest of the other pumps system. With both pumps at the same setpoints the pump closest to the demand should do most of the work.

With distance between the pumps you might also be able to just offset the start setpoints by 5-10 lbs & set shutoff the same. MikeD74T

 

[SLOBuds]

The fighting can occur when the demand pressure is just below the start setpoint of the second pump. With the first pump running & demand keeping the system pressure just below the second start setpoint, the second pump start can boost pressure quick enough to shut it's self off & pressure will immediately drop back below the start point of the second pump. This is short cycling.MikeD74T

I thought that bladder/pressure tanks removed that possibility. So when the first pump got pressure just below start point of the second pump, it would take time to fill the pressure tanks attached to both of the pumps. It would not be possible to boost pressure fast enough for a short cycle.

Maybe I am asking this wrong by providing an solution first. I would like to have a backup pump that would kick in and work in the case where my primary pump stopped. How can I accomplish that?

Thanks.

 

[Kays Supply]

Almost every rural water district has booster pumps along the runs to maintain pressure. The booster has its suction taken off the feed downstream of a main pump. If a system is built in series not parallel, that would work the same as a multistage pump. One boosting the other. I have no input on parallel systems.

 

[Egon]

Maybe draw and post a schematic.

 

[SLOBuds]

Maybe draw and post a schematic.

OK, here's the design.

There is about 1200 feet of 2" PVC between the 2 pumps.
Each pump would have a pressure tank.
Each pump would draw from a separate water storage tank.

 

[Egon]

The chances are very good that you will only have one pump running most of the time. The other pump will only kick in if the demand rate is large enough that the first pump cannot maintain pressure.

 

[SLOBuds]

The chances are very good that you will only have one pump running most of the time. The other pump will only kick in if the demand rate is large enough that the first pump cannot maintain pressure.

You think they will 'fight'?

 

[tommu56]

If you surge is in short duration you would only need more pressure tanks by the flow.

Instead of another pump I would put 4 or 5 more pressure tanks on the system by the houses then your existing pump will run longer but short bursts would come out of the tanks.

tommu