exterior sump pump
#1
07-27-11, 07:12 PM
exterior sump pump
How do you size an exterior sump pump and pit? I'll have 100' of footer drain and the soil is mostly sand. I am thinking about putting a 2' diameter pipe from ground level to about 2' below the footer. Not really sure how you get the pump in and out though. Can you just let it down by the discharge pipe? It would be about 7' or 8' to the bottom of the pipe.
#2
07-28-11, 06:18 AM
Group Moderator
You try to size the pump the handle the amount of water you need to pump. You need to know (or guess) how much water will be flowing into the pit and you also need to consider the size of your pit. If your pit holds 30 gallons a large pump with drain it very quickly and then turn off while a smaller, less expensive pump may take 30 or so seconds to drain the pit. Both will work but the smaller may be more proper for the application and save you some money. If you expect water will be flowing into the pit at a good rate you may want a larger pump to keep up with the flow.
If you are using rigid pipe I would install a coupling that you can easily access from the surface so the pump can be easily removed for servicing. I tie a rope to the handle of the pump and lift it by that. You don't want to break your plumbing by using it as a lifting handle. Make sure to secure the other end of the pump's rope somewhere near the surface so you can raise the pump in the future.
If you are using rigid pipe I would install a coupling that you can easily access from the surface so the pump can be easily removed for servicing. I tie a rope to the handle of the pump and lift it by that. You don't want to break your plumbing by using it as a lifting handle. Make sure to secure the other end of the pump's rope somewhere near the surface so you can raise the pump in the future.
#3
07-28-11, 02:59 PM
Are there methods for determining the estimated flow rate or is it really just a guess? I have the perc test information from the septic install, just not sure if that would be of any use. How deep below the footing would you install the pit? Is 2' enough or should I go deeper so that it could hold more water? Do I need to seal the bottom of the pit some how?
#4
07-28-11, 03:34 PM
I have seen a couple of outdoor sump systems and they both used a 36" diameter x 10' deep pit so your 2' below footings are probably about right. All the pits we have already have bottoms. What were you thinking of using? Sizing could be difficult until you have something in the ground. Put the biggest you can afford then you can determine how much water you have to deal with and size the pump. You also have to have a good place to pump all of that water away from the house so your not pumping the same water over and over.
#5
07-28-11, 05:12 PM
Group Moderator
Once you know the size of your pit you can calculate it's volume. Then once it's installed you can monitor how fast the water enters. That will give you an idea about the flow rate at that time. The guesswork will come in determining the flow for different times of year, seasons and weather. You also need to decide if the pump should be able to keep up under the worst of conditions.
I think the most popular pumps are between 1/2 and 1 hp.
I think the most popular pumps are between 1/2 and 1 hp.
#7
07-30-11, 07:07 AM
The pump has to get rid of water faster than new water enters the pit but does not necessarily have to empty out a large pit quickly. So you might not need that large or expensive a pump.
The guessing game has to do with what the maximum worst case inflow gallons per hour is.
Regardless of the size of the pit, if the water level is is allowed to get high enough to submerge the ends of the perimeter drain pipes (weeping tiles; French drain pipes) then the perimeter drain system will stop working, the soil all the way around the foundation will re-saturate and basement flooding may resume.
The guessing game has to do with what the maximum worst case inflow gallons per hour is.
Regardless of the size of the pit, if the water level is is allowed to get high enough to submerge the ends of the perimeter drain pipes (weeping tiles; French drain pipes) then the perimeter drain system will stop working, the soil all the way around the foundation will re-saturate and basement flooding may resume.
