Door Closers: Controlled Closing, Backcheck, and Latching

How a Door Closer Works

LCN, an Allegion closer brand, summarizes the principle: "The power to close the door is generated by the springs inside the closer. Regulated hydraulic circuits control the speed of the door's closing swing."

Inside a typical surface closer:

• Arm system: connects the closer body to the door or frame and turns the door's swing into rotation at the closer.
• Pinion: per LCN's glossary, it "transfers rotary motion of the arm system to the piston."
• Piston and spring: the rotating pinion moves the piston, which compresses the spring as the door opens.
• Hydraulic fluid and valves: as the spring pushes the piston back, fluid passes through regulating valves that set closing speed.

The Closing Cycle and Its Adjustments

LCN describes the door cycle in stages. Backcheck cushions the opening swing near full open, a main speed controls the long closing arc, and a latching arc brings the door to "a quiet, secure close." Allegion's knowledge base says LCN and Falcon closers have three regulating valves and a spring adjustment, plus a fourth valve on closers with delay:

• Backcheck: adds hydraulic resistance near full open. Allegion stresses that backcheck is meant "to slow the door down, not to stop the door." Where the door must stop at a set position, a stop arm or overhead stop does that job.
• Main speed: controls the door from wide open to about the last 15 degrees before the latch.
• Latch speed: controls about the last 15 degrees, so the door closes gently but still latches.
• Delayed action (on closers so equipped): holds back the start of closing to give extra time to pass through.
• Spring power: sets how much closing force the closer produces, which also changes how hard the door is to open.

Temperature matters too. LCN notes that hydraulic fluid thins as temperature rises, so the door closes faster, and thickens in the cold, so it closes slowly. All-weather fluids reduce the need for seasonal adjustment.

Mounting Types and Arms

Closers are either surface-mounted or concealed. ANSI/BHMA A156.4 covers closers that are surface mounted, concealed in the door, overhead concealed, and concealed in the floor, along with pivots used with floor closers. LCN says closers concealed in the door itself are recommended for interior doors only.

LCN's catalog shows three standard surface mountings:

LCN also lists specialty arms, including hold-open arms, stop arms ("Cush-n-Stop"), and a fusible link arm that releases its hold-open function when exposed to high temperatures. The BHMA A156.4 numbering system includes a listed fusible-link holder arm among its closer types.

Closer size refers to minimum spring power. LCN's sizing tables are set up by ranges of door width under normal conditions. Doors of exceptional height or weight, or doors exposed to drafts and air-pressure differences, may need more closer power.

Accessibility and Closers

Closers have to meet two needs: enough force to close and latch the door, and little enough force that people can open it. The 2010 ADA Standards set two closer-related rules for accessible doors:

• Closing speed (404.2.8.1): from an open position of 90 degrees, the time to reach 12 degrees from the latch must be 5 seconds minimum.
• Opening force (404.2.9): interior hinged doors are limited to 5 pounds of force. Fire doors are excluded from that figure and instead "shall have a minimum opening force allowable by the appropriate administrative authority."

LCN cautions that a manual closer adjusted for reduced opening force "may not provide sufficient power to reliably close and latch the door," and points to automatic operators where both goals must be met. Local code and the AHJ decide which requirements apply to a given opening.

Closers on Fire Doors

An NFPA technical services engineer, writing on NFPA's site, says fire doors "must be kept closed and latched or arranged to be automatic closing during the time of a fire," and that "blocking or wedging doors in the open position is prohibited." Fire doors must also be inspected and tested after installation and at least annually under NFPA 80. That includes an operational test to confirm the assembly will close and latch.

Where a fire door is held open in normal use, the hold-open has to let it close automatically. LCN's guide specification describes combination closer/holders "designed to hold the door in the open position under normal usage and to release and automatically close the door under fire conditions," and LCN catalogs these as life safety closer/holder release devices under ANSI/BHMA A156.15. Which arrangements are acceptable on a given door is up to the applicable code and the AHJ. See fire-rated door hardware for the wider picture.

Standards

BHMA's summary of ANSI/BHMA A156.4-2024 (Door Closers and Pivots) says Grade 1 door closers must pass two million cycles of opening and closing on a test door of a specified weight. The door-control tests cover range of checking control, two speeds of closing, adjustable closing speed, cylinder checking, overload abuse, and opening angle. The standard also assigns type numbers to closers and arms. See ANSI/BHMA lock grades for how BHMA grades work across product families.

An Early Patent

LCN's name and company history trace back to Lewis C. Norton. One record of his work is U.S. Patent 868,357, "Door-check." It was filed March 13, 1906, and granted October 15, 1907, to Lewis C. Norton of Newton, Massachusetts, assignor to the Norton Door Check Company of Boston. The patent describes a check that retards movement in both directions using liquid in a cylinder. It also provides ports so that "the speed of the movement of the object may be controlled throughout its entire extent instead of merely during any particular part of the movement." That idea of speed control across the whole swing survives in the adjustable valves of modern closers.

Related Topics

• Panic hardware: exit devices that depend on doors closing and latching
• Electric strikes: access control that works with a closed, latched door
• Electromagnetic locks: holding a closed door with magnetism
• Door latches: the latch a closer must drive into the strike
• Fire-rated door hardware: self-closing and positive latching
• ANSI/BHMA lock grades: how BHMA grading works

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