Piping for sump pumps

[Russell]

I am going to install a second sump pump into the same pit as a back up. Can anyone tell me what size pvc pipe to purchase so that if they would both start running could handle the flow? The pumps have 1.5" discharge pipes coming out of them. Once again what size pipe do I need to run these two lines into to handle this?



Russ
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[jwwing]

I would consider making the output of the new one T into the first one's output beyond its check valve and put the new one in the sump hole an inch or two above the old one so that it doesn't turn on until the other one fails to turn on. I would put a switch on both of them so that I could run either without the other independently allowing me to operate the second one alone sometimes to make sure it works ok. If both run at the same time, it should only be for a very short time till the second one turns off and water should shoot out of the output pretty quick.

If this idea is not good to you, use either two separate output pipes or one pipe with a cross section area equal to two times that of the old pipe - rnew = 1.4 x rold, I think so a 1" dia pipe should be replaced with a 1.4" diameter, but I bet a 1.5" would work just fine.

 

[johnjh2o]

I would consider making the output of the new one T into the first one's output beyond its check valve and put the new one in the sump hole an inch or two above the old one so that it doesn't turn on until the other one fails to turn on. I would put a switch on both of them so that I could run either without the other independently allowing me to operate the second one alone sometimes to make sure it works ok. If both run at the same time, it should only be for a very short time till the second one turns off and water should shoot out of the output pretty quick.

If this idea is not good to you, use either two separate output pipes or one pipe with a cross section area equal to two times that of the old pipe - rnew = 1.4 x rold, I think so a 1" dia pipe should be replaced with a 1.4" diameter, but I bet a 1.5" would work just fine.

I would think that the size pipe needed to handle both pumps at the same time would be determined by the by the flow rate of the pumps.

John

 

[jwwing]

I would think that the size pipe needed to handle both pumps at the same time would be determined by the by the flow rate of the pumps.

John

You are absolutely correct. The flow rate of the pumping system is determined by the output pipe size though as well as the pump's capability. So if the output port size is known and the output pipe of the system was properly sized, a reasonable flow rate for the current pump can be assumed to be provided by it. To determine the flow rate for a pipe to satisfy both pumps at the same time the sizing can quickly be accomplished by calculating 1.414 x rold since it goes as the square of the radius. Assuming that both pumps are the same to satisfy its purpose, the second pump should be expected to be as capable as the first. So a single pipe of proportional size should provide satisfactory results.

I would not recommend this method (increasing pipe size) unless the original pipe was somewhat damaged or known to be too small. The best method is to T in as I originally suggested, but we don't know all of the circumstances.

In general, the output flow rate increases as the size of the pipe increases. If you install a 1/2" pipe to a 1.5" output port, the flow rate will be only slightly less than max, but it might well be satisfactory, depending on the situation. The pressure will be increased and the water will flow faster than it would had a 1.5" pipe been used. My suggestion should provide a similar design point to that of the original pump system, assuming that the two pumps are similar in capacity.