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  1. #1
    Join Date
    Apr 2010
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    4

    Default How short a sump pump cycle is too short?

    I've read about short cycling and wonder if I have that problem. I have a 1/3rd HP pump in a 20" diameter well that's about 30" deep, maybe a bit deeper. I have a float switch which has a fairly long throw from off to on. When the pump turns on, it empties the pit in about 10 seconds. On the worst days it may actually turn on every 35 seconds (for 10 seconds per on time). On most days it runs less often, more than one minute between on times. Of course there are actually many days throughout the year when it doesn't run, but in wet seasons it does run most days. The good news is it keeps the basement dry even in the rainiest March on record here in Boston (15" rainfall or more this month).

    So the question is, is the pump on time too short?

    A wider diameter pit would increase the pump on time and off time. But it would be hard to make the pit larger (basement is finished). I guess the easy thing is to replace the pump more often since the frequent cycling might be wearing it out.

  2. #2
    Join Date
    Mar 2010
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    31

    Default Re: How short a sump pump cycle is too short?

    You did not mention it, but you do have a check valve on the outgoing line, to keep discharge water from draining back in the pit?
    A bigger concern that I would have is how much damage would you experience in half day with a failed pump?
    Consider putting in an alarm to warn you of overflowing water. They only cost $13-20 and are battery operated.
    Would you ever consider cutting out a second pit and installing a second backup pump that would only receive water overflowing from the first pit if the first pump failed.
    There are battery backup secondary pumps that can be installed on top of the primary pump. They do require maintenance on the battery and can be a little difficult to install.

  3. #3
    Join Date
    Aug 2007
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    The Great White North
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    4,045

    Default Re: How short a sump pump cycle is too short?

    Quote Originally Posted by john9 View Post
    I've read about short cycling and wonder if I have that problem. I have a 1/3rd HP pump in a 20" diameter well that's about 30" deep, maybe a bit deeper. I have a float switch which has a fairly long throw from off to on. When the pump turns on, it empties the pit in about 10 seconds. On the worst days it may actually turn on every 35 seconds (for 10 seconds per on time). On most days it runs less often, more than one minute between on times. Of course there are actually many days throughout the year when it doesn't run, but in wet seasons it does run most days. The good news is it keeps the basement dry even in the rainiest March on record here in Boston (15" rainfall or more this month).

    So the question is, is the pump on time too short?

    A wider diameter pit would increase the pump on time and off time. But it would be hard to make the pit larger (basement is finished). I guess the easy thing is to replace the pump more often since the frequent cycling might be wearing it out.
    If the the pump empties the pit in 10 seconds then the "on time " isn't too short.

    I also argree with the mention of the check valve.Without one --- when the float switch shuts off the pump all the remaining water in the discharge line will empty back into the pit adding to raising the water level in the pit.

    Other things to consider is to ensure the discharge line outside and downspouts are extended well away from the foundation.

    Other than that it seems things are doing what they are intended for ---- drains are spilling into the sump pit --- the sump pump is discharging the water.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #4
    Join Date
    Apr 2010
    Posts
    4

    Default Re: How short a sump pump cycle is too short?

    Thanks for the replies. I really appreciate them.

    I've put a lot of effort into making the system reliable and I just was worried that the pump cycle was too short. Since posting my first question, I've browsed the web some more and noticed that practically all sump pits are about my size and if you use the kind of switch I use (vertical float switch) it's kind of impossible to have a longer "on" time. I pump about 8 gallons per cycle, plus or minus, just based on the diameter of my pit and the vertical distance of the switch throw from on to off.

    There are other switch choices. I have no experience with the diaphragm types. There's the tethered float switches but they kind of have too much throw, resulting in much longer cycle times but also the water gets much deeper before the pump turns on. Perhaps vertical float switches on pedestal pumps are longer throw and longer cycle. No experience there either. There's even the float switches attached to little computer that turn on the pump for a fixed time, but that too easily runs the pump dry.

    I do have a check valve. In fact, I also have a basement watchdog back-up pump and have separate check valves for each pump prior to the outlet pipes merging in a Y (those are 1.5" PVC). The basement watchdog acts as an alarm and backup. It also records transient failures with its LEDs. So if you unplug the main pump altogether, the basement watchdog LED shows pump failure, even if you then reconnect the main pump and it starts working again.

    My primary pump is an AC pump that is battery backed up with a charger-inverter set up to power the pump with AC current from big AGM deep cycle batteries which charge when power is on. That charger-inverter unit has the AC transfer switch contained in it. I test the systems at least 2 times per year, prior to the known wet times. I put a garden hose in the pit dumping water, and then disconnect power to test each part of the system in sequence.

    My main concerns with the basement watchdog is that it hasn't got enough power for a really long outage, and the batteries come empty from the store and you have to handle battery acid from a stupidly design container-dispenser. The dispenser has a plastic tube coming out that can fly around and literally throw battery acid. It would be nice if they would fix that or switch to AGM or other sealed batteries.

    So overall, I just need to keep up with the maintenance. Battery replacement, system testing, and pump and switch replacement if they start to look old even while they test out fine. I keep a spare pump by the the pit and a spare switch somewhere around here (I should put it by the pit too).

    Anyway, thanks again for the replies.

  5. #5
    Join Date
    Apr 2010
    Posts
    4

    Default Re: How short a sump pump cycle is too short?

    One more note. I do have the discharge taken care of. That's a good and important point you made. In my case there was essentially no good place to put the water from my pump on the property, but the town allowed me to make a storm sewer (not sanitary sewer) hookup and I dump underground straight into the storm sewer. Wish I had another option. This was expensive and it doesn't help the storm sewer system in bad storms.

    When I bought the house, they had already finished the basement and they were illegally dumping the sump pump into the sanitary sewer. I'm doing better than that at least.

    Personally, I'd try not to finish a basement given other alternatives. But this is the house we've got.

  6. #6
    Join Date
    Apr 2010
    Posts
    4

    Default Re: How short a sump pump cycle is too short?

    Well I decided I didn't want 20K in damage to my basement and to be put out by all that would entail. We could get serious water in here and have to do a lot of reconstruction. So I took the necessary measures. It's not that hard to set up a good system, though it's surprisingly hard to get the information.

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