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What Is A Grinder Pump: Here Is Everything To Know

I am pretty sure you have heard of grinder pumps. Your home may be equipped with one even though you may not know many things about it. So what is a grinder pump?

A grinder pump is a type of sewage ejector pump with a grinder to chop any solid wastes in the house’s sewage while pumping it uphill. The grinder pump pumps sewage from houses where the toilets and other fixtures are below the main sewer line.

This article is written with the intent to tell you everything about grinder pumps.

A grinder pump station
A grinder pump station

More about grinder pumps

Grinder pumps pump the wastewater coming from a house situated below the main sewage line in the area. Since the main sewage is situated higher, the water from the house will not drain by gravity. So to remove the waster water, it needs to be pumped into the sewers.

You can do this by using a sewage pump. However, if the wastewater has to be pumped far uphill, a regular sewage pump won’t be able to do that as the head requirements (the height to which sewage needs to be pumped) are high. Therefore, a special type of pump called a grinder pump is used.

Like I mentioned above, grinder pumps are sewage pumps but with a grinding mechanism. This grinding mechanism grinds solids like human waste, toilet paper, an occasional sanitary pad, etc, and it prevents the pump from clogging. Since the solids are ground to fine sizes, they can be pumped out through an outlet pipe of a smaller diameter like 1.25 inches. Using a small outlet pipe helps to pump the sewage farther, thus increasing the total height to which the sewage can be moved. This is why grinder pumps have higher heads than standard sewage ejector pumps.

A brief history

Grinder pumps were invented by the engineers in General Electric during the end of the 1960s. They were made to address the increasing usage of pressure sewage systems during that time. Since around 50% of the land in the USA is not suitable for septic tank systems, pressure sewer systems were introduced vastly. Even though sewage pumps were used to pump the sewage uphill, the head requirements often exceeded their capacity. Moreover, occasional clogs were a headache. As a solution to this, some engineers in General Electric came up with the idea of a grinder pump.

Types of grinder pumps

There are different type of grinder pumps. They are;

Centrifugal and semi-positive displacement

Based on the pumping mechanism there are two types of grinder pumps;

  • Centrifugal
  • Semi-positive displacement type

Most grinder pumps are centrifugal type. They have an impeller connected to their motor. The impeller creates a centrifugal force to create a continuous flow of fluid in one direction.

A positive displacement type pump uses a displacement action to move the liquid up. This type of pump is used where the head requirement is high. The displacement actions exert more force on the water so that it can be pumped farther away.

115 volt and 230 volt grinder pumps

There are grinder pumps that run on a 115 volt supply, and those run on a 230 volt supply. But most of the grinder pump models available in the market for residential use can run on both these voltages supplied.

Vertical float switch vs tethered float switch

Many grinder pumps come with an automatic start and stop mechanism. This mechanism can be a vertical float switch or a tethered float switch. Both types of switches are good, but tethered switches are used for large and deep sewage collection pits. Besides, most grinder pumps use this type of switch instead of the vertical float type.

Residential and commercial

Grinder pumps can be used for residential or commercial applications. As you might have guessed, the pumps used in commercial buildings are more powerful than those used in houses. This is because you have control over what goes into the toilets in your house while you don’t have that in a commercial building. So people may be flushing down things like flushable wipes, feminine hygiene products, and even cloth pieces into the toilet in a public building. So the grinder pump used there should be able to grind all these items without getting clogged.

Automatic vs manual

Most grinder pumps work automatically. They start when the water level inside the grinder pump station (a basin where the wastewater from the house is collected) exceeds a certain level and stops when this level drops below a preset point. This is done with the help of float switches. Automatic pumps are suitable in houses where the pump stations get filled up frequently.

But, there are also grinder pumps that need to be run manually using a switch. These pumps do not use float switches. They are suitable in houses where the sewage needs to be pumped only occasionally.

Types based on horsepower rating

Grinder pumps come in many horsepower ratings. The most common power ratings are 1/2 HP, 3/4 HP, 1 HP, and 2 HP. The more the horsepower is, the more height to which it can pump sewage. The cutting torque of the grinding mechanism also increases with the motor’s horsepower rating.

How does a grinder pump work?

Grinder pumps are used to pump a house’s sewage into a sewer line situated uphill. The main parts of a grinder pump are;

  • A motor
  • An impeller
  • A cutter
  • A casing
  • A switch

The motor is directly connected to the cutter as well as the impeller. The impeller and the motor sit inside the casing while the cutter mechanism is at the bottom of the pump. When the pump runs, the sewage enters through its bottom side, passing the cutter before moving into the pump. The motor is tightly from water and moisture using O-rings. It is usually kept immersed in oil to prevent it from overheating.

Here is the detailed working of a grinder pump system;

  • The wastewater from the house is collected in a basin buried in the yard. It is called a pumping station.
  • The pumping station is where the grinder pump is installed. It has an inlet to receive the sewage from the house and an outlet to pump the sewage into the municipal sewer system.
  • When the level of sewage collected in the pumping station exceeds a preset level, the grinder pump starts running. It will grind and pump the sewage into the main sewers.
  • Once the level of the sewage falls below a preset point, the pump stops working and waits for the station to be filled up again.

Types of wastes it can handle

A grinder pump shouldn’t be used as a trash can. Just because it has a grinding system to handle solid wastes, it is not the replacement of a trash can. I have seen youtube videos where grinder pumps are used to dispose of even denim, but that won’t work in practice.

It may be able to handle a sanitary pad occasionally, but if you keep flushing down such items into the toilet, the pump will eventually fail. Here are the solids a grinder pump can handle;

  • Human waste
  • Toilet paper
  • Food wastes (Ya, it’s okay to flush them down the toilet.)

I am very sure that you expected a longer list. Unfortunately, these are all you can put down the toilet.

That being said, some manufactures assure that their products can manage feminine hygiene products and diapers. But take that with a grain of salt, and dispose of these items in the garbage can. Grinder pumps are expensive, so do not put anything you shouldn’t.

Head vs flow rate: The importance of performance curve

A grinder pump is chose based on your head and flow rate requirements ie, how high you need the sewage to go, and how fast it needs to go. The maximum head and flow rate are always mentioned in its specification sheet; however, what you have to remember is that these parameters are related and inversely proportional.

Let me clarify.

The pump needs to exert more force to pump the sewage to higher heights. This is done by sacrificing the flow rate. For example, a pump that can move 20 gallons of water per minute to a height of 20 feet won’t be able to maintain the same flow rate to a height of 30 feet. In the latter case, the flow rate will be less than 20 gallons per minute.

This means that as the flow rate increases, the height to which the sewage can be pumped decreases, and vice versa. This relationship between head and flow rate can be plotted on a graph, and it is called the pump’s performance curve.

Zoeller pump performance curve
An example of a performance curve

The specification sheet of every grinder pump comes with this performance curve. You can find whether the pump will deliver the head and flow rate you need by referring to this graph. Therefore, it is vital to check the performance curve before deciding on a purchase.

Applications: When do you need a grinder pump

A grinder pump is required only if;

  • the house connects to a low-pressure sewer system
  • the sewage needs to be pumped far uphill

When the house is connected to a low-pressure sewer system

Unlike gravity sewer systems, a low-pressure system doesn’t require gravity for the sewage to flow. Its movement is powered by the use of grinder pumps.

Since a grinder pump chops all solids from the house’s sewage into fine particles, the contents in the pressure sewer system are basically water. This means that the sewage can pass through the sewer lines without clogging and without the need for gravity or lifting stations.

Since pressure sewer systems are designed this way, it is mandatory to use grinder pumps if your house is connected to such a system. You won’t be able to use a regular sewage ejector pump here as it allows the solids to pass through, which will finally clog the sewer system.

When the sewage needs to be pumped far uphill

Another scenario where you need to use grinder pumps is when the head required is high, i.e. if the sewage needs to be pumped to high levels. If you need to lift the sewage to a height of more than 30 feet or send it to a distance over 1000 feet, a grinder pump is the right choice.

Since the grinder pumps chops all solids, it needs only a small diameter pipe to eject sewage to the sewers. This means that such a pump can pump sewage farther than a regular ejector pump with the same horsepower rating. This makes a grinder pump more ideal for such jobs.

Grinder pump vs sewage ejector pump

There is a wide belief that grinder pumps and sewage pumps are the same. But they are different in many aspects. And unlike many people believe, a grinder pump is not an upgraded version of a sewage pump.

Here is a quick overview of the differences between both types of pumps;

Grinder pumpSewage pump
Has a cutter mechanismNo cutter mechanism
Grinds solids into a fine slurryLets solids up to 2 inches to pass-through
No clogging if properly usedMore likely to clog than a grinder pump
Can pump sewage to far distancesCannot move sewage as far as a grinder pump can
Lower flow rateHigher flow rate
Suitable for low-pressure sewersSuitable for gravity sewers
A comparison between grinder pumps and sewage pumps

As you can see, most of the points in the above table are already discussed. But read further to know more.

A grinder pump grinds all solids coming to it. But a sewage pump lets solids up to 2 inches in size pass through it. This means that these solids end up in the main sewer system. Any solids larger than 2 inches will clog a sewage pump, so it is essential to check what you put in the toilet. A grinder pump can manage solids even if you accidentally put something that doesn’t belong there.

Grinder pumps clog more than sewage pumps. Yes, I know I said otherwise in the table above. The reason is, people put everything down the toilet when they have grinder pumps. This includes solids these pumps can’t handle, which logs them in the end. But if used properly, a grinder pump is unlikely to clog.

Sewage pumps come with an outlet size of 2 inches, while grinder pumps come with 1.25-inch outlet pipes. It is this small diameter of the outlet pipe that helps it to move sewage farther than a sewage pump. However, this comes at the cost of the flow rate. A sewage pump can move a much larger volume of sewage when compared to a grinder pump.

Common grinder pump problems & solutions

Grinder pumps are not without problems. In fact, they can cause more problems than sewage pumps because people tend to throw everything into the sewage when they have a grinder pump.

Here, let’s discuss the common problems of grinder pumps and their solutions;


Grinder pumps are unlikely to clog if used properly. However, people tend to dump down whatever they have into the house’s sewer system, which can cause a clogged pump. Things like flushable wipes a common cause of clogging. Flushable means they will pass through the drain pipes; it doesn’t mean that the wipes will dissolve in water. Other items like paints, pet food, feminine hygiene products, makeup wipes, towels, etc, which find their way into the drainage pipes, end up clogging the grinder pump.

A clogged grinder pump
A clogged grinder pump

Things like zip ties also clog grinder pumps. These items are very likely to get ground if the pump is operating. But if it enters the grinder when it is stationary, the zip tie will prevent the grinder from moving once turned on. This is because the cutter won’t have enough cutting torque at the start to chop the zip tie.

Unclogging a grinder pump

You can unclog a grinder pump only by lifting it from the pumping station and cleaning it with water. Its cutter and inlet should be checked for any debris clogging it. You should remove this debris and then manually rotate the cutter and the motor to ensure it is free from debris.

Once the obstructions are removed, and the pump is cleaned, it is put back into the pumping station.

Unclogging a grinder pump

A faulty float switch

Most grinder pumps are run automatically using a float switch. The float of the switch floats in the sewage. It rises when the level of the sewage rises, and once it reaches a certain preset level, the float triggers the switch, which turns on the grinder pump.

Any problems with the working of the switch can affect the pump. A faulty switch can cause the pump to keep running when the sewage level is low. It can also cause the pump not to turn on even if the sewage overflows.

The float switch can stop working due to the accumulation of debris and grease on it. Also, if the switch has a hollow float, water may be leaking into it, making it inoperative.

If the switch is faulty, the only solution is to replace it. You can also buy a piggyback switch to bypass the existing one.


In places with cold climates, one should install a grinder pump below the frost line. If it is installed above, the pump and sewage will get frozen, making the system inoperable.

If this happens, there isn’t much you can do. What you can do is reinstall the whole pumping station deeper, and this is going to take extensive work.

A quick and temporary solution is to cover around the pumping station with dirt to increase its effective depth. This will prevent freezing to some extent.

Warning: I have seen some youtube videos where the pumping station is opened, and the pump is covered with plastic. While this method works, I urge you to check with the local authorities as you can be liable for tampering with the pump.

Buying a house with grinder pump

Many people prefer to buy a house that uses the traditional gravity sewer system. In such cases, the house owner doesn’t have to worry about any sewage issues. But if a house uses a grinder pump, it will need to be maintained or replaced every four or five years. This can be a costly affair considering that these pumps are not cheap.

For this reason, many people are not willing to buy a house having a grinder pump. But how good is this reason? Does a grinder pump reduce home sale value?

There is nothing wrong with buying a house with a grinder pump. A grinder pump doesn’t reduce the home sale value either. These pumps are cheap to run, and they do not require any preventive maintenance. By watching what goes into the sewage, one can add more years to the life of a grinder pump.

My name is Thomas Anderson, and I have worked briefly as a plumber. Even though I am currently working on a different career path I still help out my friends and family with their plumbing issues. This is a hobby blog where I share my knowledge with the audience through random articles. Through this blog, I hope to address some common questions about garbage disposals.