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Sump Pump & Rain Water Issue

I live in a condo building that has a sump pit for collecting rain water only(no solid waste) from front and back patios and downspouts. In that pit are two 1/2 hp sump pumps that pump out into a single 1.5" copper pipe (2 pipes join together with 'Y' fitting) that rises around 10 - 15 feet and out (overhead plumbing in building).

My question is this: Does the 1.5" copper pipe have enough capacity to handle the outflow from both pumps running full out during a heavy rainstorm?

A few times a year, the pit becomes overwhelmed and I need to run a hose out to the street and drop an extra pump into the pit to keep from flooding. Water level in pit rises above level of inflow pipe, so water starts backing up into patios and water starts to leak into to sliding glass door in rear of my condo. So, do I need a wider pipe to handle the outflow, or a third pump with a second outflow pipe to handle things? I freak out every time we have a severe thunderstorm warning.



Re: Sump Pump & Rain Water Issue


Every pump will have something called a "head loss curve" which you can get from the manufacturer of the pump.

Typically, the head loss curve for a pump will be a concave down parabola with the vertical axis being the pressure (in feet of water) the pump has to pump against and the horizontal axis being the flow rate in gallons per minute.

What's killing you is the 10 to 15 foot column of water those two pumps have to pump against. Sump pumps typically are made to pump against a head of water that's not much higher than the depth of the sump pit.

Similarily, the piping you have will have a similar head loss curve, but this one will be a parabola that's concave up. Anyone listed under "Pumps" in your yellow pages phone directory can help you work out what the head loss curve for your piping is if you know the length and size of the pipes and the number of 45 and 90 degree elbows in it.

The flow rate at which the head loss curve for the pump intersects the head loss curve for the piping is the rate at which water will be pumped out of your sump pit by each pump. How you'd add in the increase in pressure in the piping to account for the operation of the other pump is something I don't know.

However, it seems to me that someone has already added a second pump to that sump pit because they were having the same difficulties as you. In my opinion, I'd look for a way to avoid that 10 to 15 foot vertical rise you have to pump against. If that's not possible, then you might need to go to a different kind of pump. There are "effluent pumps" that are meant to pump out septic systems that will pump effluent up 40 feet into the air. A properly sized effluent pump will have no trouble with the 10 to 15 foot rise your sump pumps appear to be having difficulty with.

I'd look under "Pumps" in your Yellow Pages and see if you can get someone working as a sales agent for any of the various pump manufacturers to compare the head loss curves of each sump pump with the piping you have to determine whether the situation would be completely different if you didn't have to pump your sump pit water up 10 to 15 feet to get rid of it.

Re: Sump Pump & Rain Water Issue

Pretty much all sump pump lines we deal with are 1-1/2 inch per pump. I would say that single 1-1/2 is not large enough and is causing restriction which reduces both pumps outputs. The 10-15 foot rise shouldn't be an issue and is not uncommon -- most sump pumps I've worked with include that rise in their specifications.
Either the existing line should be at least a 2 inch or two seperate 1-1/2 inch lines -- imo

Re: Sump Pump & Rain Water Issue

What they said plus;

When calculating head pressure (and/or back pressure) you have to add in not only the rise of the pipe but also the number of 90ยบ turns. Each turn adds to the back pressure.

Re: Sump Pump & Rain Water Issue

Thanks for your input on this issue.

I have lived in this building since it was originally built in 98. With the building boom, it seems like many builders took some short cuts to save some $$$. I was responsible for getting the 2nd pump unit installed into the pit at the suggestion of the plumber I had in to check it out. This solutions covers us about 99% of the time. But a few times a year, we get a downpour that overwhelms this system.

The vertical rise is unavoidable. I live in the city of Chicago. Buildings are being built so that the water from any common sources and waste water from any garden level units have to be piped up between the ceiling of the garden unit and the floor of the 1st floor unit (overhead plumbing). That way if the sewers get overwhelmed, water is not backing up into the buildings.

I had a plumber over here yesterday to check things out. He kind of stated what I already believed. Either the piping leading out of the building will have to be changed from 1.5" to 2". Or, we might have to dig an overflow pit and install a 3rd pump and an additional 1.5" or 2" pipe leading out the sewer. This will be tough because the current pit is in a pretty confined area underneath the common stairs at the front of our building. Either solution will mean ripping out some sections of wall and ceiling drywall in one of the garden units and digging to get to the sewer line. I assume this won't be very cheap.

My one concern with the plumber I had over was that he didn't seem like he could tell me conclusively if the current 1.5" pipe could handle the water flow of 2 separate 1/2 hp pumps. Shouldn't a plumber be able to calculate this? Do I need to call a Master Plumber? I don't want to end up guessing on a solution that will probably be very expensive.

Thanks again for your time. I really appreciate any advice I can get on this.


Re: Sump Pump & Rain Water Issue

Most residential plumbers never run into these types of calculations, so they don't need to know where to find the info.

Call the pump manufacturer or dealer to get the info.

Re: Sump Pump & Rain Water Issue

Canuk, Thanx for keeping it simple! :)
With the flow rates and head pressure loss even from a cheap pump, you are never going to exhaust 2, 1/2 horse pumps, which are going to have 1-1/2" outlets into a continuous 1-1/2" exhaust line. You are restricating the gallons per minute greatly and over working the pumps, shortening there lives. Increase the pipe sizing at the connection of the 2 pumps 1-1/2" lines to 2" or greater. Not knowing the square footage of your roof and both patios, I can not give you an accurate pump size or gallons per minute needed to clear this area of water in the heaviest storm, which is how this pump and pipe sizing should be calculated.
In simple and understandable terms to you Dutlir, Increase pipe sizing at 2, 1-1/2" line connections to 3" if it is possible, see if this resolves the issue. worst case scenario with this pipe increase already done, you can up the size of your pumps any time after this to increase flow rates with no restrictions. Saving you time and money from building another pit or having to increase exhaust line size in the future.
Hope this helps, Chris

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