Sump pump model and switch level

Discussion in 'Pumps and Tanks Well Forum & Blog' started by pitter, Dec 13, 2010.

  1. pitter

    pitter New Member

    Messages:
    2
    Location:
    Ohio
    Background:

    I recently bought a house with a 1600 sqft basement (floor is 7 feet below the ground level). Two weeks ago there was a lot of rain and the basement had 4" of standing water within a few hours. It turned out that the old sump pump (a Simer 1/2 HP, 1900 gph @10 ft) stopped working. The water receded within 24 hours, but the sump pit was still almost full.

    After reading online forums, I decided to replace the pump with a Zoeller. Today I installed a Zoeller M98 pump in the pit. This pump is sitting on a layer of bricks at the bottom of the pit. It rained yesterday, so the pit was almost overflowing today before I installed the pump.

    When I turned the pump on the first time, it took 45s for the pump to lower the water level in the pit and then turn off. After that, there was an alternate cycle of the pump turning on, and off (water was rushing into the pit from the drain pipes while the pump was off). At first, the pump on time was about 10s and the off time was 12s. About an hour later this went down to an on time of 8s and an off time of 20s.

    The diagram below shows the water level in the pit when the pump turns on. It also shows the pit dimensions (18" diameter and 22" deep), the drain pipe heights from the bottom of the pit (9" and 10"), and the water levels at which the pump turns on and off (11" and 6"). I believe the drain pipe on the right (9" above the pit base) has a much longer run than the other drain pipe.

    [​IMG]

    As you can see in the diagram, the pump does not turn on until there is about 11" of water in the pit. Since the drain pipes are 9" and 10" above the pit base, the pump does not turn on until there is some standing water in the drain pipes.

    Questions:

    1. Do I need to adjust the pump float switch so that the pump turns on before the water level in the pit reaches the drain pipes? This way, the drain pipes won't have 1-2" of standing water in them before the pump turns on. In a slow season, it may take a few days for this much water to seep in the drain pipes. This means that the drain tiles below the basement floor could be quite wet before the sump pump even turns on. If I should reduce the turn on height, how would I do this? Options I can think of are to put a spacer at the top of the float slide bar, and also to replace the bricks at the bottom with something of a lower height.

    2. Would the Zoeller M53 be a better fit than the M98? I am concerned that the M98 pump may be too powerful and so cycling too much. The water discharge is about 10 feet above the pump outlet. Since the M53 would take longer to empty out the pit, the incoming water from the drains may just keep that pump from turning off at all. The M98 is 1/2hp and pumps 3600 gph at 10 feet. The M53 is 1/3 hp and can pump 1900 gph at 10 feet. I do plan to finish the basement soon, and so don't want to have a situation where there is heavy rainfall, and the sump pump is not powerful enough to keep up with the heavy rain. Of course I don't want to see the pump cycling too much and burning up either.
  2. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    M53 is more than plenty at such low head.

    Why pump it so low? If you are into the average groundwater level you are pumping fruitlessly.

    Perhaps test pumping a few inches of water level only and allow a few inches of water to stand in the drain pipe. You might get 10s on and 2 hr off in a normal weather.
  3. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD

    3600[10/(10+12)] = 1600 gph
    3600[8/(8+20)] = 1000 gph

    You might want to find the 5 year, 10 year and 20 year rainfall for your area. For Ohio it is 2.8"/hr based on a 1 hr storm that comes back every 100 years.
  4. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,232
    Location:
    Land of Cheese
    The M98 is too much pump for that basin. As Ballvalve mentioned, there is not much benefit in trying to pump the drain tile dry, particularly if the water table is coming up to the pumped level. At that point, you are just wasting electricity and wearing on the pump. The goal of the system is to ensure the water level is maintained below the bottom of the slab. Even with the M53, the life of the pump motor would benefit greatly by installing a wider basin.

    If you haven't yet, start with a complete review what is happening outside your house. Many wet basements can be fixed by proper grading of the surrounding yard, along with routing rain gutters and sump discharge to prevent the water from coming back to the foundation. In many places a french drain can be installed to redirect large amounts of water so that it does not reach the house in the first place.
  5. pitter

    pitter New Member

    Messages:
    2
    Location:
    Ohio
    When it is not raining the water level in the sump pit is usually significantly below the drain pipes feeding in. Hence the drain tile is generally dry.

    Would you recommend I return the M98 and get an M53 instead? Or am I ok with the M98 even though it is too much pump for the basin. I would rather have a heavy duty pump there in case it is ever needed, but certainly don't want it to die prematurely due to excessive cycling.

    I am planning to put in a WatchDog Big backup sump pump in a few months.
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,232
    Location:
    Land of Cheese
    The longer the pump runs without stopping the better. The M53 will move over 30 GPM given your head. Ideally, the basin should be sized to keep the run time at a minute or better.
    If your incoming flow is greater than that and your can't fix the problem from the outside, I would recommend going with an alternating twin pump system. (particularly if you plan on finishing the basement)
  7. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    What are recommended ways of tweaking pumps that turn out to be oversized to give less GPM?
    You could drop the voltage with a buck-boost transformer wired to buck the supply voltage but it might shorten the life of the motor.
  8. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,232
    Location:
    Land of Cheese
    Some would say to choke back the flow with a control valve but the increased thrust wear or potential for cavitation would not bear well on the life of the pump. If you knew you would never need the full pumping capacity it would be better to create a "leak" in the outlet that would recirculate a percentage of water back to the sump. It would be more cost effective to properly size the pump in the first place.

    If you want to work on something Thatguy, you could build a VFD sump pump that uses the rate of water flowing into the sump as a control input. :eek:
    Last edited: Dec 15, 2010
  9. Thatguy

    Thatguy Homeowner

    Messages:
    1,460
    Location:
    MD
    I'm on it.
    http://en.wikipedia.org/wiki/PID_controller
    Can you forward me some bucks so I can hire illegals to produce this thing???

    The second half of this document shows more or less everything you wanted to know about sump pump sizing
    http://www.aspe-norcal.org/resources/ASPE Sewage and Sump Pump Sizing 9-9-08.pdf
    Compare your duty cycle and pump size with what this site would recommend.

    Here's the general search
    http://www.google.com/search?client=safari&rls=en&q="sump pump sizing"&ie=UTF-8&oe=UTF-8
    Last edited: Dec 16, 2010
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