How Does a Sump Pump Work?

by | Feb 25, 2016 | Blog, Plumbing | 0 comments

What is a Sump PumpHeavy rainstorms, mild flooding, or heavy plumbing damage all run the risk of flooding out your home.  However the water got into your home, it will try to collect at the lowest point first (usually your basement).  With a working sump pump, the damage from water seepage will be minimal.

A sump pump collects water in a basin and pushes it outside of your home.  The collected water can be returned to a dry well or the city’s storm drains.  What matters is that the water is being direct away from your home and not right back into the flow that’s entering your home.

Older homes used to tie the sump pump directly into a city’s sewer system.  If your sump pump is connected to your washing machine’s water return line, then this is the case for your home.  This kind of system can overburden the sewer system so it is no longer compliant with city codes.  If you see this in your home, we advise calling a licensed plumber to redirect the line.

How it Works

It’s all well and good to know what a sump pump does, but how does something that small keep such a large volume of water from flooding your basement?  The answer, as usual, is science!  Your sump pump consists of:

  • Gravel-Bottomed Basin or Pit
  • Pressure Sensor or Float Valve
  • Centrifugal Pump
  • Return Pipe
  • Check Valve

As water flows into the pit, it activates your sump pump by raising the pressure on the sensor, or simply raising the float valve (this is for automatic sump pumps, we’ll cover manual pumps in a moment).  The pump is actually an electric motor which turns an impeller (a type of fan or screw) to move water within the basin.  As the impeller pushes water away, more flows in to the fill the void near the impeller, which forces water to move out through the pipe in the basin.  As it leaves via the pipe, a check valve blocks the water from returning, leaving it only one avenue of escape.

Sump Pump Types

While sump pumps are made up of many different components and come in multiple styles, the key measurements to consider when purchasing or replacing your sump pump are:

  • Pedestal or Submersible
  • Manual or Automatic
  • Pressure Switch or Float Valve
  • Head Pressure
  • Power Source

Visually, the biggest difference in sump pumps is whether the motor is suspended above the pit, or placed inside.  Submerged sump pumps are nicer to look at because the pump isn’t hovering above the pit as a visible piece of machinery.  The drawback comes with maintenance and repair. A submersible sump pump is harder to work on because it’s difficult to reach.  Most repairs will require a complete removal which takes extra time.

For manual pumps, they simply wait for you to turn them on.  Obvious drawbacks are that you can’t turn on the pump if you aren’t there.  For an automatic pump, take notice of how the pump is triggered.  Both float valves and pressure switches are triggered by water depth.  As depth increases, the pressure on the switch increases until the switch is tripped (more water = heavier weight = higher pressure).  Float valves simply float on the surface of the water, once the valve reaches a certain height, the pump activates.  One important difference:  Pressure switches are usually enclosed and can’t be adjust but also are not affected by junk or small trash, unlike float valves.

Head pressure is another factor to consider.  This is simply a rating that tells you how high a pump is capable of pushing water.  Measure the height of the pipe from the base of the sump basin.  You want to make sure that height (which is exactly how high your pump is going to pushing water) isn’t more than 80% of your pump’s rated head pressure.  This is to help your pump operate efficiently and prevent it from burning itself out with heavy loads.

One last thing to consider before buying a new pump:  How is it powered?  Battery backups and main line power are the options you have, but you might want to consider springing a little extra for having both.

Pump Testing

You should test your sump pump regularly.  As emergency equipment, when it needs to operate you don’t have time to spend on fixing it.  Once water moves into your basement it’s there to stay unless you act fast, and even an inch of water can cause a lot of damage.

The simplest way to test your pump is to pour a couple gallons of water into the basin itself.  For automatic pumps, it should trigger immediately and begin pumping water out.  Have someone watching the outflow pipe to make sure water is flowing away from your home as intended.  Wait until the pump is finished to make sure that your sump pump actually disengages.  This is especially true for submersible pumps.  Submersible pumps are designed to be cooled by the water they’re moving, and have the potential to burn out when left to run in dry air.

If the pump engages, removes all the water from the basin, and disengages successfully then the test is complete and your pump is in good working order.  It’s a simple test, so it’s best to check on your pump every month, or at least every three if you don’t have the time normally.


Protect your home from water damage by having Boulden Brothers install, maintain, or repair your sump pump!

Boulder Brothers is available to answer any electrical and home generator questions you may have. Your safety and comfort are out highest priorities. Feel free to give us a call at (302) 368-3848; we are available 24 hours a day, 7 days a week.

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