White Paper: Not Your Grandfather's Brushed Vacuum Blowers ... Anymore


When it comes to the commercial market, brushed motors have been a staple in the industry for years. Whether it’s for scrubbers, extractors or central vacuum systems, these motors are considered critical because of their durability and dependability.

Thanks to cutting-edge technologies and ongoing research, brushed vacuum motors have evolved. Over the last 30 years, they have become smaller, lighter, and faster. Additionally, there has been a significant improvement in components. Bearings can now reach 50,000 to 70,000 RPMs, while commutators, brushes, and fans are capable of taking on higher speeds and lasting a normal lifetime.

Brushed vacuum motors are often used in these commercial applications because of their ability to deliver optimal performance. In this whitepaper, we’ll look at:

  • What makes brushed vacuum motors unique
  • Bypass vs thru flow motors
  • Considerations for application design
  • Moisture protection
  • Instructions for changing brushes in our various Lamb® motors

What are Brushed Vacuum Motors?

Brushed vacuum motors are based on a universal motor design, which uses a wound rotor and stator in series with one another. Universal motors are most commonly found in smaller, corded appliances, and have high speed and good starting capability. Their speed-torque characteristics make them ideal for driving fan loads.  They speed up as load decreases, and partly compensate for clogging filters in vacuum cleaners. The workhorse of many applications, these motors have a high horsepower-per-pound ratio and are generally less expensive than their brushless counterparts.

Design and Speed

When it comes to your application, you may have several goals to consider: vacuum or pressure, airflow, cost, life and noise are just a few. Brushed motors are less expensive than their brushless counterparts, however they do not provide the same life expectations. That’s something an engineer will have to balance.

If cost is more of a concern, brushed motors are the solution because of their cost effectiveness. While brushless motors do provide longer life, there is a cost for the magnets and technical aspects of brushless motors. Brushed motors deliver a lot of performance relative to cost.

When it comes to speed, brushed motors are fast. Historically, their standard speed was 15,000 to 25,000 RPM. Recently, however, their design has become more economical and material-savvy which has allowed the standard speed to increase to between 30,000 and 40,000 RPM in many models. Some designs routinely run 40,000 to 45,000 RPM, while others exceed 50,000 RPM.

Bypass Motors

In bypass motors, the working air is independent from the cooling air. A separate fan is used to direct cooling air over the armature and field. They are used when it’s important to ensure the cooling air doesn’t mix with the vacuum or blower air.

Bypass motors come in peripheral and tangential discharge configurations and are available in single or multiple stages. The purpose of the stages is to create more pressure or vacuum.

Since the working air does not travel across the motor, bypass motors are a great option for scrubbers, carpet extraction, and other wet pickup applications because debris and moisture will not contact the motor windings directly. They are not, however, designed to pump water.

DFS Bypass Motors 

For bypass motors:

  • Working air ≠ cooling air
  • Separate cooling fan
  • Separate paths; can safely handle moist air
  • Tangential discharge, bypass motor

DFS Three stage peripheral bypass vacuum motor

Three stage, peripheral bypass vacuum motor

Thru-Flow Motors

In thru-flow motors, the working air travels through the fan system and is discharged directly over the motor windings as it exits. This allows the working air to provide the cooling air for the motor. Thru-flow motors come in single- or two-stage and are ideal for dry vacuum conditions since the working air also cools the motor.

DFS Thru Flow Motor

For thru-flow motors:

  • Working air = cooling air
  • Restriction in working air restricts cooling ability of motor

DFS Single Stage Flow thru vacuum motor

Single stage, flow-thru vacuum motor

How to Determine the Ideal Design for Brushed Vacuum Motors

Since there are a variety of brushed vacuum motors available (currently over 1,400 unique AMETEK models), there are certain questions you should ask to determine the ideal design for your application. Some of these questions include:

  • What type of air will be picked up? Ask yourself if you need a motor that has to pick up dry or moist air.
  • What are the cooling requirements? Figure out whether external cooling will be necessary or if there is enough working air flow for cooling. Will some sort of thermal protection be required?
  • What will be the operating point? Determine what kind of airflow rate, pressure or suction, current draw or input power will be necessary.
  • What type of voltage type? Understand the available operating voltage. Will you need an alternating current (AC) or direct current (DC) motor?
  • What is the use case? Find out whether you’ll need a brushed motor for pressure or vacuum purposes.
  • What other features do you need? Does your application require thermal protection? Need serviceable brushes? Air discharge (tangential, peripheral or thru-flow)? Specific life?

By taking the time to think about the answers to these questions and collaborating with one of our experienced engineers, you can determine the right design for your needs. 

Protecting Bearings Against Moisture

At AMETEK Dynamic Fluid Solutions, our Lamb® brushed motors take the worry out of protecting bearings from moisture damage. We use a revolutionary air seal technology where a fan creates a localized pressure. The pressure pushes moisture-laden air away from the bearings to keep them free of contaminants.

In addition, we use a Gore-Tex® washer. The Gore-Tex® washer goes up against the shaft and right below the bearings on their pressure side. It works to create a physical sliding seal and keep moisture away rather than using pressure to blow it away. Some motor designs incorporate both air seal technology and Gore-Tex® washers.

We prove our designs by using a specialized life test to ensure optimal moisture protection. The test exposes the bearings to water and detergent and proves the effectiveness of the bearing protection.  We also choose precision ball bearings with specialized greases and seals for additional protection.

DFS Air Seal Detial

Air Seal Detail

Changing Brushes

The brushes inside these motors will wear out, depending on how often the motor is running, and the type and volume of debris being moved. Fortunately, brushes on Lamb motors can be easily changed by the end user.

The following section describes how to change the brushes on a 5.7” vacuum motor, 6.6” low voltage motor, and 6.6” curved brush motor.

5.7” Vacuum Motor

Step 1. Remove the power from the motor. Take a flat blade screwdriver and bend back the metal safety clips so they are no longer over the plastic cap.

DFS 5.7 inch vacuum motor step 2


Step 2. Use the screwdriver to pry up on the plastic cap to pop the cap loose. Once the cap has been removed, the brush mechs should be exposed.


Step 3. Take the flat blade screwdriver and locate the brush clip. Using the screwdriver, press down firmly and push the clip towards the center of the motor. The clip should slide out from under the black nylon of the brush mechanism.

DFS 5.7 inch vacuum motor step 3


Step 4. Once the clip is free from the brush area, remove the two screws holding the brush clamp in place.

DFS 5.7 inch vacuum motor step four


Step 5. After the two screws have been removed, lift the clamp up and remove the brush.

DFS 5.7 inch vacuum motor step five

DFS 5.7 inch vacuum motor step six


Step 6. Install the new brush. Start the brush clip into the nylon and use the top bracket of the motor to press the clip all the way in place. Put the brush clamp in place using the two screws.

Step 7. Repeat this for the second brush. Once done, press the black plastic cap back into place until both sides click. Then, bend the metal safety clips back so that they help hold the plastic cap in place.


6.6” Low Voltage Motor

Step 1. Disconnect the power source to the motor before starting the brush change. Remove the two screws that hold the black plastic cap in place.

DFS 6.6 inch low voltage motor step 1


Step 2. Remove the plastic cap to expose the brushes.

DFS 6.6 inch low voltage motor step 2


Step 3. Locate the two screws that hold the brush clamp in place and remove the screws.

DFS 6.6 inch low voltage motor step 3


Step 4. Move the clamp off to the side.

DFS 6.6 inch low voltage motor step 4


Step 5. Remove the old brush.

DFS 6.6 inch low voltage motor step 5


Step 6. Insert the new brush, replace the clamp, and tighten the two screws to hold the clamp in place.

Step 7. Repeat this procedure for the second brush. Once the second brush has been replaced, place the cap back on the motor and replace the two screws that hold it in place.


6.6” Curved Brush Motor

Step 1. Before starting, disconnect the motor from the power source.  Then, remove the screw holding the ground wire on.

DFS 6.6 inch curved brush motor step 1


Step 2. Remove the two screws holding the black plastic cap on.

DFS 6.6 inch curved brush motor step 2


Step 3. Remove the black cover. Now, pull the brush spring back and lock it in the back position.

DFS 6.6 inch curved brush motor step 3


Step 4. Cut the shunt wire as close to the carbon as you can.

DFS 6.6 inch curved brush motor step 4


Step 5. Use the crimp connectors that came with the brush kit to attach the new brushes to the end of the shunt connected to the field.

DFS 6.6 inch curved brush motor step 5


Step 6. Slide the carbon back into place and release the brush spring so that it is in the slot on the carbon.

DFS 6.6 inch curved brush motor step 6


Step 7.  Repeat for the other brush. Once both new carbons have been installed, replace the black plastic cap. Then, secure it with the two screws and reinstall the ground lead.

The AMETEK Difference

AMETEK Dynamic Fluid Solutions is a global manufacturer of a wide range of motors, blowers, fans, and pumps. Our products serve a plethora of applications such as central vacuum and commercial floor scrubbers and vacuums, paint sprayers, pet dryers, fume evacuators, lawn and garden tools, food and beverage appliances, and medical applications. If it moves air, chances are that an AMETEK DFS motor has been used to do it. Since 1915, we’ve used innovative technology and best practices to provide the most cost-effective solutions for all air moving applications.

We take great pride in closely collaborating with our customers to ensure they select a product that matches the specific requirements of their application. Regardless of what you’re designing, our field sales and application engineers are here to help.

At AMETEK DFS, we understand you’re looking for more than just an off-the-shelf part or one-time solution. You need a true technology partner who understands your engineering challenge and is focused on providing you customized, collaborative solutions. We’ll also provide you with excellent customer service for a great total experience.