Sump Pit Sizing

Hello "Guest"

Before a proper answer may be given, you would need to advise several factors not yet known:

1. Layout of building (A sketch would assist, with dimensions)
   
2. Is street water able to run down the entry/exit ramp?
   
3. Possibility of flooding during monsoon etc
4. Size in floor area
5. Number of cars/trucks etc expected plus maximum of same
6. Fire sprinkler capacity in quantity per hour per sprinkler (More than one sprinkler may emit water in a vehicle fire)
7. Stormwater outlet capacity (you have to pump sump water somewhere)
8. Are there other vehicle floors above? - advise how many, and if the top floor is open to the weather or roofed over please
   
9. Other useful factors - Advise please.

Reply here, with

Kind Regards....

the condition is in middle east so no storm water runoff to be considered. consideration is just draining the car park for cleaning purposes (which is seldomly done). It is a 3 level basement parking. So if little water (washdown) flow rate is being considered, is there a minimum flow rate in the code say 20 gpm to be the minimum pump size..then just consider 15 minute retention time for the volume of the pit?

Hello ericpolc

<"....the condition is in middle east so no storm water runoff to be considered....">

Even in the "Middle East" sudden unexpected heavy rainstorms have occurred during the last few decades, on a sporadic basis.

Thus the "Stormwater runoff" situation is a serious consideration, even though this may not happen for several years.

It would be prudent to allow for such sudden rainfall.

Those qanats and cisterns hewn from rock were often filled by brief but heavy rainstorms.

If you have a basement park full of customer's cars, and they float in water, then sink, because of something you didn't allow for, those customers are going to take it out on your hide, and that would be very unpleasant, believe me.

Kind Regards....

Most important detail to consider: comply with your local Codes-of-Practice for factors like minimum retention time, minimum required flow etc.

shound like a simple 2 hp sump pump would cover all your needs easy.

First: I should say that I know nothing about this sort of thing, so, just ignore me if I'm being stupid.

It seems as though you need a pit shaped a bit like this:-

The small pit will accommodate the small pump for routine duties, and, the larger pit will hold water caused by an emergency. The small pump would empty the large pit eventually, but, I guess the local fire service would do it if there had been a fire or flood for other reasons.

Of course the main pit could be covered with something strong enough to support the expected "traffic".

Your pit size is probably not as important as your pumping capacity. In order to design that you need to know your flooding sources and rates.]

The fire suppression system will have a good flow and losing all the cars on the lowest level to flooding might make someone unhappy. Electric failure during emergencies is pretty common so there may be no helping this.

Storm flooding is difficult to predict but there will be data for the area somewhere.

Ground water seepage is typically all these systems are designed to handle. Insurance is there to cover the rest.

If that is the case here, I think the 2hp pump sound about right and good drainage and a small - 0.25 to 1.0 cu meter sump would be ok. If you need more sump capacity buy a plastic tank and bury it. It will cost a lot lot less than forming a sump pit out of concrete.

Best wishes,

Mr. Gee