Security Gates TutorialBy Benros Emata, Published Jun 05, 2012, 12:00am EDT
While gates are a critical component for many facilities, selecting them can be challenging. Numerous types of gates exist with various tradeoffs in operations, security, aesthetics and safety. In this note, we examine 5 types of gates and explain their operation and best applications.
Automatic gates control access into a secured area. Most commonly, they are deployed at the entrance to the facility to control vehicular access on and off of the site. For example, a manufacturing plant may use an automatic gate at its main entrance. All vehicles entering and exiting the plant must do so through the automatic gate. Automatic gates are also used at interior areas within a facility. For example, automatic gates are commonly used within the inside of a parking garage to separate employee parking areas from public areas of the garage.
Components of an Automatic Gate
Automatic gates consist of two basic components:
- Gate: The gate is the physical object moved to block the gate opening. Most gates used in commercial applications are made of either ornamental iron or chain-link material and are usually designed to match the fencing next to the gate.
- Gate Operator: The gate operator is the machinery that moves the gate in and out of the gate opening. Gate operators are electrically powered and may be chain-driven, gear-driven, or hydraulic depending on the type of operator.
Types of Automatic Gates
There are five types of commonly used automatic gates:
- Slide gate
- Cantilever gate
- Swing gate
- Vertical lift gate
- Vertical pivot lift gate
- Barrier arm gate
The following is a brief description of each type of gate and their best fits.
The slide gate is probably the most commonly used type of automatic gate in light-duty commercial applications. Here's what a slide gate looks like:
The slide gate is mounted parallel to the inside of the fence and slides horizontally back and forth across the gate opening. The slide gate uses rollers on the bottom of the gate to support it. These rollers typically ride along a metal track that has been installed along the ground across the gate opening. Slide gates are sometime also called "rolling gates" or "V-track gates".
Because this type of gate uses rollers that must run along the ground, there can be problems with the rollers getting blocked by snow, ice, or debris. The rollers can also be a source of friction, making the gate operator have to work harder to open and close the gate. Due to these issues, some gate operator manufacturers discourage the use of slide gates.
The cantilever gate is similar to the slide gate, but does not use rollers that slide along the ground to support it. Instead, the cantilever gate is supported from rails that run along the inside of the fence structure. This gate gets its name from how it "cantilevers" (hangs over) the gate opening. Cantilever gates need to be much wider than slide gates to allow a section along the fence structure where the gate is supported. This section is called a "counterbalance" and is usually at least 1/2 the width of the gate opening itself.
Here's what it looks like:
Cantilever gates are suspended across the gate opening from the counterbalance, with no rollers running along the ground to avoid friction and obstruction. Because of this, most consider cantilever gates to be more reliable than slide gates, and are commonly used for heavy-duty and industrial gate applications.
One downside to using cantilever gates is the additional width required to accommodate the counterbalance. This can be a problem at sites that have limited space available beside the gate.
Swing gates are hinged on one side and swing open and closed like a door. Swing gates typically travel a 90 degree arc between their open and closed positions. Swing gates can consist of a single leaf or double leafs and can be in-swinging or out-swinging.
Swing gates are most commonly used in residential applications because of their low cost and ease of installation. Because swing gates travel over a large arc, space must be available to allow vehicles approaching the gate to remain clear while the gate opens or closes. The swinging arc of the gate also raises extra safety considerations to prevent people or vehicles from being hit or trapped by the moving gate.
Vertical Lift Gate
Vertical lift gates move up and down vertically over the gate opening. The gate must be lifted high enough to allow vehicles to pass underneath of it. This type of gate requires that tall vertical support towers be installed on each side of the gate opening.
Here is what it looks like in action:
Vertical lift gates are ideal when space is limited next to the gate opening. Vertical lift gates are also very fast and very reliable. However, the vertical support towers gives these gates a very "industrial" appearance, which may make them unsuitable for use in locations where appearance is important.
Vertical Pivot Lift Gate
Vertical pivot lift gates rotate in and out of the gate opening. Vertical pivot lift gates are supported entirely from the gate operator itself and require no added support structures.
Vertical pivot lift gates provide some of the benefits of vertical lift gates, but appear less obtrusive as they do not require vertical support towers. However, the footprint of a vertical pivot lift gate operator is larger and requires additional space beside the gate. Vertical pivot lift operators typically use springs to serve as a counterweight, and in our opinion, this makes them less reliable than a standard vertical lift gate.
Barrier Arm Gate
Barrier arm gates consist of a vertical barrier arm that is rotated in and out of the gate opening. Barrier arm gates are used to control vehicles, not pedestrians. As it is very easy for a person to walk beside or climb over or under the gate arm, barrier arm gates provide minimal security.
Barrier arm gates are used primarily to control access in and out of parking facilities, or to control vehicular traffic at manned security entrances.
Automatic Gate Accessories
There are many accessories that may be used in conjunction with automatic gates. Some of these include:
- Access control systems: Automatic gates can be operated by a variety of access control devices, including card readers, vehicle tag readers, digital keypads, and portable wireless transmitters. In most commercial installations, automatic gates are controlled by the same access control system that is used to control the entrance doors to the buildings, allowing the same access card to be used in both places.
- Intercom systems: Intercom stations are often provided at automatic gates to give visitors and delivery drivers a means to contact someone inside the facility when the gate is closed. Most of these systems will allow the gate to be remotely opened by someone inside the facility once the visitor's identity has been verified.
- Video surveillance systems: Video cameras can be used to view and record activity at the gate along with the intercom system, allowing visual confirmation of visitors before opening.
- Free exit devices: In many cases, it is desirable to have the gate open automatically when a vehicle exits the property. Devices that can be used to provide free exit include loop detectors, photoelectric beams, and pressure switches.
- Post office and utility company access: The post office and many utility companies may require a means to enter through the gate. This usually requires the use of one or more key-operated switches that are keyed to the post office's or utility company's standard key.
- Emergency access: Most fire departments and many law enforcement agencies require a means to gain access to your property through your gate at all times. Devices used to provide access can include key boxes (Knox Boxes), strobe or siren activated sensors, and radio receivers that can be activated by the emergency vehicle's two-way radio.
Gate Safety Devices
Automatic gates can weigh as much as 20,000 pounds or more and can travel at speeds as high as 36 inches per second or faster. As a result, gates have the potential to cause serious property damage, injury or death. Therefore, it is extremely important that safety considerations be included when planning any type of automatic gate installation.
The primary guideline for automatic gate safety is Underwriters Laboratories (UL) Standard 325. This standard defines classes of automatic gate operators and the various techniques that should be used to prevent entrapment and reduce the potential for injury. Gate safety measures can include warning signage, audible warning devices, photoelectric sensors, contact (pressure) sensors, screening, safety cages, and other devices.
Because some of the requirements of UL 325 are difficult and costly to implement, many gate installers have chosen to downplay or ignore these requirements. It is often easy to get away with this because there is little enforcement of these standards in many parts of the country. However, the property owner who installs an automatic gate that is in violation of recognized standards does so at his own peril and may be held liable if someone is injured by the gate.
Considerations When Choosing an Automatic Gate
The following are some basic things that must be considered when choosing an automatic gate:
- Opening size: The overall size of the opening will be a major determining factor in deciding what type of automatic gate to use. In general, the wider the gate opening, the more expensive it will be to install a gate. While gate widths of over 80' are possible, gate widths over 40' tend to be more expensive and more problematic.
- Availability of Space: the amount of space available on all sides surrounding the gate can limit the type of automatic gate that can be used. If the facility is located on a large rural site that has plenty of space, probably just about any type of automatic gate can be used. Facilities located in crowded urban or downtown areas where space is at a premium may be limited to only one or two options for automatic gates.
- Weight of gate: The overall weight of the gate determines the type and grade of gate operator required. In general, the wider and taller the gate, the more it will weigh. Gates of the same size will weigh differently depending on whether they are constructed of steel, aluminum or wood. Allowance must also be made for any increase in weight that may be caused by accumulations of rain, snow, or ice on the gate surfaces.
- Opening and Closing Speed: Different applications require different opening and closing speeds. While slow opening speeds can be acceptable in residential and some commercial applications, they are totally unacceptable in high-volume industrial applications such as at a distribution center or airport. Opening speeds that are too slow can cause traffic backups and user frustration. Closing speeds that are too slow can encourage "tailgating" and other security violations.
- Duty Cycle: The number of times the gate will be opened and closed each day must be considered when selecting an automatic gate operator. Certain types of gate operators designed for residential use may only be intended to be cycled a dozen times per day or less. These types of gate operators will fail quickly in an industrial environment where the gate is cycled hundreds of times per hour on a 24 per hour per day, 365 day a year basis.
- Grade: Most gate operators are designed to operate gates that are on a level, flat grade. Gates that must open or close going up or down an incline can cause excessive wear on the gate operator and lead to premature failure.
- Gate Construction: Simply adding a gate operator to a gate that was originally designed for manual operation can be a real mistake. Gates need to be specifically designed for automatic operation. Special types of rollers, bearings and other hardware are often needed to make a gate work reliably with an automatic gate operator. These items add relatively little cost to the overall installation, but make a big difference in gate performance and reliability.
- Weather Conditions: Special precautions must be taken when installing gates in regions where there are extreme hot or cold temperatures, high winds, or heavy snow or ice.
- Location: The type of neighborhood where the automatic gate is being installed must be considered when specifying a gate. In general, gates being installed near residential areas(where children are likely to be present) require more stringent safety measures than gates being installed in purely industrial environments.
- Electrical Power: While some light-duty gate operators will work with standard 110/120 VAC electrical power, most medium and heavy-duty gate operators will require 220/240 VAC or three-phase electrical power. It can sometimes be difficult and costly to get this type of power to the place where the gate will be installed.
Deciding which type of automatic gate to use is a big decision. Automatic gates are expensive to install and require regular ongoing maintenance. Sometimes, purchasing a more expensive gate initially can actually save you money over the long-run due to reduced maintenance costs. Many architects and builders will specify the cheapest gate possible when the facility is being built. The property owner then has to live with the consequences, which can include frequent downtime and costly repairs.
NOTE: Thanks to Michael Silva of Silva Consultants who is the author of this article and can consult on making such decisions.
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