Sump pump discharge question

[MaggieD]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

 

[Lutherf]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

You've cut off about 40% of the capacity so yep, it sure would!

 

[Thom Paine]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

Ste. Maggie :
you should check local codes.. it may be an illegal discharge... I'll plce odds at 99-1

Thom Paine

 

[MaggieD]

You've cut off about 40% of the capacity so yep, it sure would!

I thought it would, Luther. Just curious. How do you figure 40%?

Thank you so much!!!!!!!!!!!!!

 

[Lutherf]

I thought it would, Luther. Just curious. How do you figure 40%?

Thank you so much!!!!!!!!!!!!!

Area of a circle is πr^ so a 5" pipe would be roughly 19.5 square inches and a 4" pipe would be roughly 12.5 so 40% less...roughly.

 

[TOJ]

I thought it would, Luther. Just curious. How do you figure 40%?

Thank you so much!!!!!!!!!!!!!

(2 x 2 x 3.14159) / (2.5 x 2.5 X 3.14159) = 0.64 assuming 4".

 

[Lord Tammerlain]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

I doubt the pump has the capacity to be restricted by a drop to 3 inch from 4.5 inch pipes.

At work we have pumps far stronger then any home market pump for pumping various liquids.

Using a standard gear pump with a 3 inch hose, it can pump about 20000 lb of water in 1 hr, a 5 inch hose might increase that to 26000 lbs. A home sump pump will not have the capacity for the different diameter to make much of a difference

 

[the_recruit]

No.

4 inches is plenty big (that's what she said) for a sump pump. Just take a look at the outlet on the pump body itself - it's probably only inch and half or so. You wouldn't see a significant difference between 4" and 5" pipe unless you were pumping at incredibly high flow rates - much higher than your little sump pump can run.

For centrifugal sump pumps, the determining factor on the flow rate is going to be the difference in elevation between the inlet point of your pump and outlet point of your discharge pipe (called the static pressure head). As long as the diameter of the discharge piping is as at least as large as the outlet diameter on the pump body, that's not going to matter much.

Might want to check that the pump suction grate isn't clogged up.

 

[the_recruit]

Area of a circle is πr^ so a 5" pipe would be roughly 19.5 square inches and a 4" pipe would be roughly 12.5 so 40% less...roughly.

Doesn't quite work like that.

 

[joG]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

It would depend on the pump, but the smaller pipe would reduce the water flow if the pump can handle that amount of water.

 

[Jerry]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

Generally, yes, it's best to keep the same diameter all the way. When you reduce diameter you increase pressure, unless you have another pipe branching off, which you didn't. This causes not only reduced flow but your pump has to work harder, which can wear out the pump itself faster.

Exceptions to above may include: If the pump isn't large enough to need the original 5" in the first place; If the pressure is needed to combat a unique landscaping challenge such as an unavoidable incline to the street (rare and unlikely); if the smaller pipe was a band-aid job don in hast and/or on a tight budget; if the local city ordinance requires a certain size which is less than the diameter of your original pipe.

 

[ttwtt78640]

I doubt that a 4" line is inadequate for your sump pump which probably has a 1.5" outlet. Ensure that the discharge line extension does not create a belly or dip in the line - this will cause added back pressure and reduce the lifting capacity of your pump. The discharge line must have a downward slope (about 1/16" drop per foot, like a gutter) or water will pool in it - probably freezing in the winter. A simple test would be to disconnect the discharge line extension and see if the problem goes away.

 

[humbolt]

Capacity of Sewer Pipes

 

[vesper]

If one part of the pipe needed replaced, is it possible that another section is also bad? Or could he have dislodged another connection while connecting the new closer to the house possibly even the downspout that ties into the drainage pipe? That would surely make the water collect in the sump at a high rate.

 

[MaggieD]

Capacity of Sewer Pipes

Hi, Humbolt. Thanks for this. I'm wondering, though, are sewer pipes under pressure? I'm thinking they're not, but...

 

[humbolt]

Hi, Humbolt. Thanks for this. I'm wondering, though, are sewer pipes under pressure? I'm thinking they're not, but...

Hey Maggie. No, such lines are not under pressure. Hopefully. Although it doesn't really apply in your instance, such lines generally increase in diameter as the length of the run increases. From what you've described, I don't think an inch and a half pump discharge emptying into a four inch line is a problem unless there are traps in the four inch line. Bear in mind that the four inch line should only be half full of water in order for it to work properly, so a low point in the travel of that line could cause problems restricting flow. If the four inch line is full of water at some point in it's run, water will not flow.

 

[TNAR]

When you reduce diameter you increase pressure, unless you have another pipe branching off, which you didn't. This causes not only reduced flow but your pump has to work harder, which can wear out the pump itself faster.

Umm... Bernoulli anyone?

A decrease in volume results in an increase in velocity and decrease in pressure.

It is highly unlikely that such a decrease in pipes would result in any problems for the pump. In fact, both pipes are probably way too large to be filled to capacity unless you're working with a pretty beefy industrial pump.

 

[Lord of Planar]

You've cut off about 40% of the capacity so yep, it sure would!

Actually, 5" ID to 4" ID is cutting the cross section by 36%. I forget the formula, but the mathematics for fluid flow is not linear for cross sectional area changes. Flow for a given pressure is probably cut more like 50% or more.

That would have to be some pump to require the 5" pipe.

 

[Lord of Planar]

I thought it would, Luther. Just curious. How do you figure 40%?

Thank you so much!!!!!!!!!!!!!

4 squared divided by 5 squared = 0.64. The 4" Id has 64% the cross section area as the 5". 36% is about 40%.

 

[Lord of Planar]

Capacity of Sewer Pipes

OK, my guess of 50% or less was wrong. Extrapolating from the chart, a 4" pipe has 57.3% the capacity of a 5" pipe.

 

[MaggieD]

Actually, 5" ID to 4" ID is cutting the cross section by 36%. I forget the formula, but the mathematics for fluid flow is not linear for cross sectional area changes. Flow for a given pressure is probably cut more like 50% or more.

That would have to be some pump to require the 5" pipe.

I'm totally guessing at the diameter. We have the same size discharge pipe, but Tom (used to have it) hooked up to a big accordian-of-a-thing pipe that carried it across the yard. Now, we have it discharging into the ground to a pipe we had run right to the storm sewer (per code). Sump pumps in the Chicago area are always a pain in the butt.

 

[Lord of Planar]

Umm... Bernoulli anyone?

A decrease in volume results in an increase in velocity and decrease in pressure.

It is highly unlikely that such a decrease in pipes would result in any problems for the pump. In fact, both pipes are probably way too large to be filled to capacity unless you're working with a pretty beefy industrial pump.

Yep.

That size pipe is unnecessary, unless it's designed for one large flow of water. Either the walls leak too much, there is storm water backup in a floor drain, the pump is not working properly, or there is a blockage in the pipe.

Maybe I missed a possibility... Anyone?

 

[Thrilla]

I noticed my mom's house has, let's say, a 5" discharge pipe coming out of the house into the front yard about 8 feet. From there, John has connected, let's say, a 4.5" pipe (maybe 4") that goes out to the street. I suggested to him that the extension should be the same diameter as the outlet pipe or it's restricting flow.

He got 3" of water in the basement during the last heavy rain. The sump pump was pumping like crazy, but was overwhelmed. Would that difference cause a signficant slow-down of water discharge?

Thanks!

nope...it wouldn't cause a slow down.

an obstruction in the suction line would, however.


he'd have to bottleneck down to under 2 inches for it to be noticed, and even then, the primary difference would be on outlet pressure ( smaller diameter at the same pump capacity would result in a greater discharge pressure


when you said the pump was "pumping like crazy", I knew he was looking at a suction obstruction or a "lost prime".... the pump, while pumping liquid at capacity, will actually operate at a slower cycle ( due to the inherent resistance of liquid)... if there is air or an obstruction in the suction line, it will "pump like crazy".. in other words, the pumps pumps a bit slower when it's full of water, it will pump a bit faster when there is air or an obstruction present

 

[Thrilla]

Yep.

That size pipe is unnecessary, unless it's designed for one large flow of water. Either the walls leak too much, there is storm water backup in a floor drain, the pump is not working properly, or there is a blockage in the pipe.

Maybe I missed a possibility... Anyone?

.. "lost prime".. air getting into the suction line somewhere between the intake grate and the intake hose coupler.

 

[Lord of Planar]

.. "lost prime".. air getting into the suction line somewhere between the intake grate and the intake hose coupler.

Yes, that is a possibility I missed.