How Slide Gate Structure Affects Automation
© 2007 Door & Access Systems
Publish Date: Summer 2007
Author: Rachel Bailey
How Slide Gate Structure Affects Automation
By Rachel Bailey, DAS Special Correspondent
As more dealers get involved in selling, installing, or servicing slide gate operators, it is important to understand how the structure of these gates affects the products that automate them. Poorly constructed gates can unnecessarily challenge gate operators.
But worse, gates not compliant with UL 325, ASTM F 2002, and ASTM F 1184 can put dealers at risk of liability. Appreciating gate system design and code compliance can help you avoid risk, minimize service calls, and extend the life of the products you sell.
“Overhead (garage door) guys are commonly asked by site owners to service a site’s automated slide gate about a year after installation,” says Shawn Davis, sales systems engineer for HySecurity, a gate operator manufacturer in Kent, Wash.
For the benefit of garage door dealers, Davis and Buck Buchanan of B & B Controls, Shrewsbury, Pa., describe the basic designs of slide gates and explain what servicing dealers should know.
Slide Gates: V-Track
The two main types of slide gates are V-track and cantilever. A V-track slide gate is constructed of angle iron that is set in concrete. Two wheels on the bottom of the gate roll in the track as guide rollers at the top of the gate keep it from rolling out of alignment.
On V-tracks, the sliding panel is three feet longer than the clear opening, which leaves room for the operator and a post to hold it up.
“These work great in the Sunbelt, but up north, V-tracks get torn out of the ground by snowplows,” Davis explains.
Slide Gates: Cantilever
With cantilever gates there are no tracks on the ground because the gate is suspended. Instead, two big posts hold it up. There are four big rollers: two on top and two on the bottom.
A challenge with the cantilever design is length. Cantilever slide gates must have a back frame, so they tend to be very long.
“For a 20-foot opening you’ll need a 30-foot gate—the extra 10 feet is the back frame,” explains Buchanan. “The back frame is a support piece that stays with the gate’s two posts to keep the gate in place.”
Buchanan says a good rule of thumb to figure length for cantilever gates is to add another 50 percent to the width of the roadway opening. (With his example for a 20-foot opening, you would add 20 plus half of 20 to get 30.)
Structural Issues: Panel Rigidity
Davis explains how flex in gate panels can inhibit the function of gate operators. Slide gate panels need to be rigid.
“Slide gate operators are designed to automate a gate that rolls smoothly in two directions; they are not intended to move the gate and not meant to support it,” Davis says.
Especially on a V-track, the gate can wobble in the middle and can falsely trigger a sensor. This can unnecessarily increase service calls and make it difficult to diagnose a problem. Flex can also damage the photo eye on gates with photo-eye accessories.
And watch out for drooping gates. Sag puts additional pressure on the gate operator.
Structural Issues: Wind Load
Davis suggests avoiding signage on cantilever slide gate panels. “At least keep it to a minimum,” he says. Wind will catch the signage, and with no track on the ground, the leading edge of cantilever gates can miss the catch at the receiving end and damage the gate edges. Damaged gate edges are a compliance issue with UL 325.
According to Buchanan, standards such as UL 325 and ASTM F 2200 were not developed as guidelines on how to properly construct gates so as to enhance the life of an operator. However, he says that being aware of the standards can help dealers avoid issues of liability.
According to Davis, standards predominantly pertain to sliding gates. They also only apply to new construction; there is nothing on retroaction, says Buchanan.
But, Buchanan warns, if someone wants to automate a 10-year-old manually operated gate (which was installed before any of the new standards were put in place), then it does need to be upgraded.
Site owners are the likely party to pay for upgrades to the gates. But anyone involved in automating the gate can be held liable if it has not been brought up to current code.
Code Issues: Spaces in Openings
“Sometimes it is not too expensive to bring a gate up to code,” Davis says. “The space issue is usually pretty cheap to fix. You can always just put a mesh backing on the gate panel.”
Basic compliance is having no openings larger than a 4" sphere. That means you can’t pass your fist through the gate anywhere below your waist. This restricts picket spacing.
“The chain-link diamond set the standard for the space allowed, and so standard chain-link fence typically meets this requirement,” Davis says. “But still, you should look for spaces between the gate and the post.”
Code Issues: Covers on Rollers
Another inexpensive upgrade is putting covers on rollers if they are not already there. This pertains to all exposed rollers (top and bottom).
Code Issues: Gates on Slopes
Watch out for gates that want to “run away.” This can happen if a gate was built on a slope. Gates built on a slope are not compliant with UL 325. However, says Buck Buchanan, there is no grade tolerance stated in the standard.
He also mentions that although you can’t run a gate up or down a slope, you can run a gate perpendicular to it.
Often, a slope or crowning exists for water runoff, Davis explains. If this is the case, even on this slight slope, the concrete needs reworking.
“Overhead guys should also at least know what type of gate class they are dealing with and what accessories are necessary to operate it,” Davis says.
Under UL 325 there are four classifications of security gates distinguished by their security level and the required accessory devices. For example, photo eyes or sensing edges are necessary for Class III gates. (For more details on UL 325 and gate classification, check the chart on DASMA’s Technical Data Sheet 353 at www.dasma.com.)
These suggestions just scratch the surface of how gate design affects the operation of automated slide gates. But, as Davis says, “If the gates you are to service don’t meet these basic standards, then don’t automate them until they do.”
Rachel Bailey is a former editor of Fabricator, the magazine of the National Ornamental & Miscellaneous Metals Association (NOMMA).