Photo courtesy Jackson & Ryan Architects
Fitting inside the tube shaft is the torsion bar, or closer spring. This torsion bar provides the closing force. The spring is tightened using torsion, as opposed to outdated coil springs, to provide durability and precision in tightening. This durability allows the torsion bar to accommodate very heavy doors, while requiring little user force.
A balanced door’s floor box holds much of the hardware in place, and also receives the door weight transferred from the tube shaft and arm assembly. However, the standard floor box is just 13 mm (½ in.) thick, 100 mm (4 in.) wide, and 178 mm (7 in.) long from interior to exterior. In addition to its weight-bearing and assembling capacities, it also serves as a convenient location for tightening the torsion bar to ensure correct tension. The torsion bar spring can be easily tightened with a wrench, as its top portion is pinned in place to the upper part of the tube shaft. It is important to note the bronze and stainless steel components within the floor box will not move unless being maintained, and therefore remain unharmed by dirt or corrosives. The author recommends contacting a door service company or the manufacturer for direction on maintenance procedures.
A final, often overlooked component adding precision to a balanced door is its semi-automatic hold-open device. As its name implies, this part keeps the door ajar without using an external element, like a doorstop. It is located in the bottom rail, and has a tapered foot pin connecting with a hole in the threshold (outside the walking path), allowing the door to remain open at its full 90-degree position. The foot pin is spring-loaded, so that a firm push is the only requirement to disengage the device and close the door.
Performance
When choosing an entry door system, architects and specifiers must consider several criteria to ensure high performance.
Foot traffic
First, anticipate the amount of traffic to the door. If the location of the door subjects it to constant use from foot traffic and exposure to the environment, the door needs to be a solid product highly resistant to deterioration and abuse. Balanced doors have a mechanical advantage—their balanced weight distribution—that allows them to offer long-term material durability.
With a conventional door, the weight is hung off the frame. Over time, screw holes elongate, causing bolts to come loose and the door to pull away from the frame, resulting in sag and drag. With a balanced door, the leaf is not connected to the frame, so the door’s weight is transferred to the bottom arm, down to the floor box, and eventually to the floor, which is much more capable of bearing weight than metal hinges. For this reason, a balanced door system lasts longer than a conventional hinged door assembly.
Conventional entry doors typically last 10 years with general use. Quality balanced doors are constructed in-house and contain parts cast and machined with high-grade materials. Therefore, balanced doors survive the test of time, generally lasting many decades with the oldest installations being 80 years and counting.
Wind and stack action pressure
The door needs to open easily and also remain closed in all conditions. When a balanced door is pulled against the forces of air, its entire surface area is not negatively impacted as it is with a conventional door. The air pressure affects both the strike and hinged sides (on either side of the fulcrum), using some of the force to assist in opening the door.
The same is true when the door closes, allowing for a more efficient closing motion. Balanced door systems facilitate fluid opening and closing, even when strong external wind pressures and internal stack pressures exist, as the door works with, rather than against, these forces. This also ensures doors remain closed (and not flutter) when confronted with uneven air pressure, ultimately reducing a facility’s energy costs.
User-friendly
The arrangement of a balanced door is such that the fulcrum is inset at one-third the width of the door—this allows for large, heavy, and durable doors to be opened with relative ease. A typical entry door has a fulcrum located on its side, which is attached to the frame with hinges, forcing the user to pull the entire weight of the assembly to open. Additionally, the weight of the door leaf hangs on the frame, constantly applying force to both the hinge and frame.
