How Sump Pumps Work

A sump pump.

Hidden in the deepest corner of your basement, your sump pump is mostly invisible, but could be the most important appliance in your house. The sump pump removes groundwater from underneath your house. Without it, water coming up from the ground, or flowing in from a heavy rain, could flood your basement or your whole house. The pump usually sits in a pit built in your basement floor or crawlspace. The concrete floor is poured slightly downhill when the house is built so that any liquid will flow right into that pit. The sump pump ejects the water out of the house.

The pump sits in the bottom of the sump hole and has a switch that is activated by the water level. When you have water in your basement, it flows into the pit, the pump is activated, and it pumps the water out of the pit through a discharge pipe to the outside.

Tip: Plumbing professional Mark Vander Sande says, “It is illegal in most states for sump pump water to discharge into the city sewer, and it is not a good idea to have the sump pump discharge water into a septic tank, as it adds water to the tank. Most sump pumps discharge outside into the yard.”

Pedestal Pumps

One of the most common types of sump pumps is a pedestal pump. In these sump pumps, a motor is mounted on a small pedestal. The entire unit usually stands about 30 inches tall. A hose or a pipe extends down from the motor to the bottom of the pit.

On a separate metal rod, there is a float. As the water level in the pit raises and lowers, this float moves up and down. This is called a float switch. When the float reaches a certain height (because the water level pushed it there), it activates the motor and the water is sucked up through the hose and ejected through another pipe. The motor on this pump is not designed to be underwater. The switch will always activate before the water level comes up to the bottom of the pump.

Submersible Pumps

Another type of sump pump is a submersible pump. It is a much smaller unit, usually about 12 inches tall, that sits in the bottom of your sump pit. Some pumps that fall within this style have a float switch on a rod just like the pedestal pump, but the rod is only about 4 inches long. The electrical switch itself is encased in a hard plastic bubble. As the water level rises, the bubble floats. When it floats so high that it reaches a vertical position above the pump, the switch is activated and the pump kicks on.

Unlike the pedestal pump, the submersible pumps don't have an intake pipe that sucks up the water that is to be sent out. Instead, the pump is located right at the bottom of the unit. The water is actually sucked right up through the bottom of the pump. There are several benefits to this type of action. First, if there is any loose gravel or debris in your sump pit (and there usually is), the submersible pump comes with a screen or a grate over the face of the pump that will prevent the debris from being sucked up into the impeller of the pump. The impeller is what creates the suction, and if it gets damaged, it's time to buy a new pump. Unfortunately, this is what kills a lot of the pedestal style pumps — the hose or pipe that reaches down into the bottom of the pit sucks up any and everything.

Ejector Pumps

If you do have an application where you need to be able to eject some small debris, then there are pumps that will do that. If you have a crawlspace that is not concrete, but just pea gravel, for example, you may need an ejector pump that can handle small debris. These are a little bit pricier, but are usually constructed of cast iron and have a 2-inch ejector port instead of the standard 1 ¼-inch port that you find on most sump pumps. This increased size and a different style of impeller allows these pumps to process small pieces of gravel and debris without damaging the mechanism.

Sewage Pumps

In rare instances, there are still applications for sewage pumps. You really shouldn't ever need one in a new house because it is illegal to handle your sewage this way almost everywhere, but in some older homes it may still be an issue. This happens when all of the wastewater in the house is funneled into the sump pit. This application is very rare and requires a sewage crock with a sealed lid for odor.

All of your dishwater, shower water, washing machine drainage and yes, maybe even the toilet, would be directed to flow right into the bottom of the sump pit. If this is the case, then you need a sewage pump that will deal with whatever solids may be flowing in.

Take the time to shop around. Whether you are buying for the first time or are replacing a unit that isn't functioning properly, you can find some great deals. Try to buy a unit with a cast iron housing as opposed to plastic. If the plastic cracks for some reason, you have open electrical components sitting in a pit of water which is not good. Also compare warranties. Most of the major manufacturers offer a full replacement lifetime warranty on their units. Make sure you register your purchase so that you can capitalize on this warranty should you ever need to.

TIP: Mark suggests, “There is usually a check valve on the discharge pipe that prevents all the water in the discharge pipe from going back into the sump hole when the pump is done pumping. If you are going to replace the sump pump it is a good idea to replace the check valve. It’s usually near the sump crock lid and is attached with stainless steel clamps and rubber connections.”