# lag lead pump question



## nolabama (Oct 3, 2007)

call back on the lift station - alternating relay is/was bad...
anyway looking thru the internet i see their is a cross wired option - it has what they are calling lead lag pumps - can someone explain this to me

I have never wired pumps to share load like this - just to switch back and forth to reduce wear - 

:thumbsup:


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## Wirenuting (Sep 12, 2010)

Lead/lag with the alternator from 1 float, single switched device
1 on both on with second float that has a double switched device, this second float has a higher position in the tank, but still uses the same lower voltage as the alternator. Wire this to the load side of your alternator.
Now if one pump isn't enough, a second pump comes on. If alternator fails then the pumps will still come on as needed, but will not alternate. 
It works good for dual equipment that isn't baby sat. The crew is untuned to walking they and will notice that they aren't alternating, so they can have a heads up to call.


Edit, I don't remember the catalog name but it has staged floats and an alternating sequencer in it also.
I posted the catalog name about a year ago.
Allied, advanced,, I don't remember but they have a web site also. Good durable stuff.


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## Big John (May 23, 2010)

I understand what a "lead/lag" does, but I've never seen the circumstance where it would be necessary. If both pumps are equally sized, why use it?

-John


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## Wirenuting (Sep 12, 2010)

Longer service life & greater rest between on cycles. 
Air compressors and large vacuum pumps for hospital systems. 

Lead/lag also gives you the chance to remove 1 motor/pump for repair and not have to halt operations. After the first one dies and you replace it, you know it's twin should be replaced as they have the identical service life put thru them.
It a preventive replacement after a reaction repair.


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## Big John (May 23, 2010)

But isn't all that achieved by just running a normal alternator?

The part I don't understand is what advantage there is to having the priority set by lag-lead? 

-John


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## Wirenuting (Sep 12, 2010)

Big John said:


> But isn't all that achieved by just running a normal alternator?
> 
> The part I don't understand is what advantage there is to having the priority set by lag-lead?
> 
> -John


Oh, I see what your getting at.
IMO, there is no advantage to a 2 pump system that is sized identical and is alternated with each start. It's a lead/lag in name only, but we know what you mean when you say it over the phone.


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## Big John (May 23, 2010)

We had lead/lag on several identical dual pump setups.

I could never see value in maintaining or replacing them when they broke, so I've just been removing them. Good to know my suspicions were right.

-John


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## micromind (Aug 11, 2007)

I don't like alternating systems. When one of the units fails, the other one has a lot of time on it, and it's being asked to do twice the work it usually does. 

In my experience, when a high-time failed unit is removed for rebuild, the other unit will very often fail before the first unit is re-installed. 

The best systems use one unit as a primary, the other as a back-up. If the primary unit is intentionally failed at regular intervals, it proves that not only does the back-up unit function, but also the controls as well. 

Very rare to find one like this though.


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## Aussielec (Apr 1, 2012)

We use the lead-lag system allot in large airconditioning and refrigeration plants. So Say if we have a 2 stage airconditioning unit-ie 2 compressors- we can designate the primary and the back up compressor through timers controlling the compressor contactors and also alternate the days each compressor acts as the lead or lag.

Not only does this reduce wear and tear on both compressors and allows for removal of one piece of equipment for service, it also prevents DOL motors from starting up at the same time, thus reducing voltage sags for the entire installation...


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## Wirenuting (Sep 12, 2010)

Big John said:


> We had lead/lag on several identical dual pump setups.
> 
> I could never see value in maintaining or replacing them when they broke, so I've just been removing them. Good to know my suspicions were right.
> 
> -John


Removal is fine as long as you can do with out the equipment for a little bit.


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## Wirenuting (Sep 12, 2010)

micromind said:


> I don't like alternating systems. When one of the units fails, the other one has a lot of time on it, and it's being asked to do twice the work it usually does.
> 
> In my experience, when a high-time failed unit is removed for rebuild, the other unit will very often fail before the first unit is re-installed.
> 
> ...


A pure alternating system does have the problem of needing to replace the second one as soon as the first goes out. But if the equipment is that critical, I'm sure there is 1 spare on the shelf. 
The second one can take a week to show up and it's not an issue. 
We always had atleast one spare o everything in the hospital. And if it was a super critical item, I kept enough to rebuild a complete system.


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## Jlarson (Jun 28, 2009)

The lag lead setup can be pretty important in some stations and not so much in others. What happens is as long as only the lead switch is tripped it acts as a normal alternator, if the level keeps rising and trips the lag is turns the second pump on as the level falls the second load goes off first then the first then the relay alternates. 

Great for systems that have high inflows during storms, recovering after a power outage, on stations with days that are particular high flow, like we have some that serve one or more churchs so Sundays are high flow days at those stations :laughing:



micromind said:


> The best systems use one unit as a primary,


The best system has 3 or more pumps and a generator so it lessens the chance I get a call out 3:00 Am Christmas day :laughing:


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## butler746 (May 7, 2012)

The best reasoning for a Lead/Lag system is if you have a plant that requires say pumps or Air Compressors to be operational at all times, and the lead unit does not work to the full load requirements of the system, then the Lag unit will kick on and help or assist the Lead unit.
Where I work we have Cooling and Sewage systems with 3 each Pumps and an Air Compressor system that has to be fully operational at all times. In these cases, this is called a Lead/Lag1/Lag2 control system. If for some reason the Lead or Lag1 can not keep up with the demand then Lag2 will kick on and assist. As the system stabilizes, the Lag 2 will shutdown automatically and the Lag 1 will shut down if the load is stabilized enough that the Lead can handle the load demand.
Thus these are highly required automatic systems that are required to maintain full load capacities at all times. In the case of a single unit is down due to maintenance or repair, the Lead/Lag control switching can be switch to set any one of the three into the Lead mode and the others Lag units could be selected to be the Lag unit, that way the one unit under maintenance or repair can be isolated and not effect the system drastically.


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## captkirk (Nov 21, 2007)

I had a similar situation in a sump pit of a building... If the one pump cant clear the pit after a given time the other one kicks on....


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## micromind (Aug 11, 2007)

Jlarson said:


> The best system has 3 or more pumps and a generator so it lessens the chance I get a call out 3:00 Am Christmas day :laughing:


That's for sure!!

Especially the generator part, and even more important that said generator actually starts when the utility fails.


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## Big John (May 23, 2010)

_Butler746,

_In the situation you describe is that purely a lead-lag function with no alternating? That makes sense.

What always confused me about the ones I saw was they were alternating duty, but you could select which equally sized pump you wanted to run in lead. If the alternator will always turn one or the other on regardless, I just didn't see the point of having priority. It made it needlessly complex.

-John


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## wesleydnunder (Mar 19, 2012)

I've worked on several lead/lag systems. The reason for them is that during most times only one pump is required to pump out the sump. Sometimes the incoming flow is more than one pump can handle, so the lag pump comes on. Also it allows a single pump to be replaced without shutting the whole system down.

In all of the systems of this type I've worked on, the system only alternates if only one pump comes on and then shuts off. If the lag pump is called for and both pumps are running, it doesn't alternate because both pumps have run. The next cycle brings up the pump that was lead on the last cycle as lead again.

Electric, Electronic and mechanical lead/lag alternators all worked this way on the sytems I've worked on.

Mark


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## Big John (May 23, 2010)

wesleydnunder said:


> ...Sometimes the incoming flow is more than one pump can handle, so the lag pump comes on....


 To be clearer, in the limited setups I've seen this function was handled entirely by the float switches. Where you either had a single two-position switch for pump 1 and pump 2 or else you had two separate float switches. 

This also sounds similar to the setup _Wirenuting _original described.

-John


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## Wirenuting (Sep 12, 2010)

ATC is the catalog I mentioned.
Automatictiming.com is their site.

Their catalog has good diagrams and functional descriptions.


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## nolabama (Oct 3, 2007)

Big John said:


> To be clearer, in the limited setups I've seen this function was handled entirely by the float switches. Where you either had a single two-position switch for pump 1 and pump 2 or else you had two separate float switches.
> 
> This also sounds similar to the setup Wirenuting original described.
> 
> -John


When you have this setup do you have four floats?


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## wesleydnunder (Mar 19, 2012)

Big John said:


> To be clearer, in the limited setups I've seen this function was handled entirely by the float switches. Where you either had a single two-position switch for pump 1 and pump 2 or else you had two separate float switches.
> 
> This also sounds similar to the setup _Wirenuting _original described.
> 
> -John


Sounds like it. The electrical/electronic alternator systems used four floats, the mechanical alternators used 2 floats.

Mark


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## nolabama (Oct 3, 2007)

You mean like this.....










Boss called and said both pumps were running. It was at the end of the day i wasnt trouble shooting with no alarm and no poo in the street, soo anyway they both 'posed to run.....


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## Wirenuting (Sep 12, 2010)

nolabama said:


> You mean like this.....
> 
> Boss called and said both pumps were running. It was at the end of the day i wasnt trouble shooting with no alarm and no poo in the street, soo anyway they both 'posed to run.....


And the piza is taped, the red bulb is burnt out, but luckily there is a 4" pipe between the poo pipe and the electrical manhole.
Now I can sleep soundly.


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