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Different Types of Limit Switches - DDM Garage Doors Blog

Posted November 2nd, 2022 at 8:04 pm by Dan Musick

Limit switches are used to keep the garage door opener from trying to open a garage door that is already open, or trying to close a door that is already closed. Throughout the history of garage doors, engineers have come up with a wide variety of limit switch designs. We have listed a few of them here.

See this article for more information about limit switches and how to adjust them.

Nut-and-shaft assembly

The most common limit switch comes in most of the Sears, Chamberlain and Liftmaster openers made since the early nineties.

An interior view of a limit switch.
As the center shaft rotates, the metal contact slides between the open and close contacts.

Another common type of limit switch found on commercial and industrial operators uses a limit shaft with two plastic nuts, as shown on this LiftMaster operator.

An image of the inside of a LiftMaster operator showing the limit nuts and switches.
The limit nuts, marked in yellow, slide to the left and right to activate the open and closed switches.

PowerMaster operators use plastic nuts with a design similar to the LiftMaster limit assemblies.

A closer look at the PowerMaster operator's limit switch.
The plastic nuts on the far right slide between the limit switches to stop the door in the open or closed position.

The older Edko operators used wooden nuts that slid between the open and closed switches.

A view of an older Edko operator with a red arrow pointing to the wooden nuts.
Notice the shaft on the left with the two hex nuts. As the operator runs, the nuts slide to the left or right to stop the travel of the door in the open or closed position.

Link operators used plastic nuts sliding along the limit shaft.

The view of a limit shaft with plastic nuts sliding on it for a Link operator.
On Link operators, the sliding nuts on top activate the limit to stop the door travel.

McKeon operators use a similar system with round plastic nuts. A steel plate prevents the nuts from turning on the shaft as the shaft turns.

An image showing the limit switches on a McKeon operator.
Here the limit switches are on the bottom. A limit chain and sprocket turn the limit shaft to move the limit nuts.

The older Crane operators used limit assemblies with two nuts.

A view of the plastic hex nuts traveling between the limit switches.
Crane manufactured limit assemblies with plastic hex nuts that travel between the limit switches. Below you can see the sprocket and chain that turn the limit shaft.

Other types of limit switches

Allister, Allstar, and MVP openers normally used chain dogs to stop the door as it opens and closes.

An image of an opener that using dogs to trigger the limit switch.
As the door operates, the chain moves in either direction to open or close the door. The dogs trigger the limit switches.

In the image below, you can see where the limit dog has moved an arm. The arm then activated the switch to stop the door travel. The limit dog can be adjusted by loosening the screw that secures the dog to the chain.

A view of a MVP opener using chain dogs to activate a stop switch.
MVP openers have chain dogs that activate a stop switch.

Historically, Genie has used limit switches mounted to the track.

A view of the Genie screw drive system using a trolley with mounted switches.
The Genie screw drive system moves a trolley to open and close the door. Installers mount the switches, so the trolley throws the switch at the open or closed position.

The older Scientific operators also used track-mounted switches to stop the door as it opened and closed.

An older Scientific operator using track-mounted switches to stop the door.
As the shaft turns, the trolley slides along the center tube, and it activates the track switches when the door is fully open or closed.

The older Vemco operators used a small tube that ran the full length of the operator rail.

An older Vemco operator using a trolley with arms at each end of a tube located in the operator's rail.
When the trolley reached the open or closed position, the trolley would raise an arm that was attached to the tube. When this end turned, an arm at the other end of the tube would turn and trigger the open and closed limit switches.

Other applications

You can also install auxiliary limit switches along with operator counters to count the number of times your garage door opens and closes. See our post explaining how to install operator counters for more information.

An auxiliary limit switch in a LiftMaster Operator

This entry was filed under History, How Garage Doors Work. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

4 Responses to “Different Types of Limit Switches”

  1. jesse Says:
    January 24th, 2024 at 4:08 pm

    Hello, Do you provide any spare parts or service or manuals for Scientific Products openers? I have an older (late 70’s) 1/2hp friction drive opener on a 12′ door. I love the unit but have had issues (starter capacitors etc). Now the unit has become unresponsive.

  2. Caleb Penney Says:
    January 25th, 2024 at 3:20 pm

    Hello Jesse. Unfortunately, we do not have any resources or products for Scientific Products openers.
    I do not see that these openers are in production anymore either, which will make it difficult to find replacement parts or manuals. I’m sorry we cannot be more helpful!

  3. Dan Musick Says:
    February 10th, 2024 at 12:23 pm

    Jesse,

    I just noticed your earlier post. I’m emailing you a picture of a Scientific operator. The switches may still be available. Please provide a picture of the switch.

    Dan

  4. Pearl. DeShields Says:
    April 8th, 2024 at 11:57 am

    Need closed limit part for. C.H.I. garage door opener.

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