Parts of a Door Closer – Labeled Diagram, Cut Open

All 18 parts on the diagram

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Start here: 7 main parts 7

Closer body Holds the spring, the piston and the fluid.
Cover Slips over the body; plastic or metal.
Main arm Turns the shaft as the door swings.
Forearm Its length adjusts to suit the door.
Arm shoe Anchors the end of the forearm to the frame.
Pinion shaft Its gear turns in the rack. The main arm sits on its end.
Spring Stores the push of opening, then closes the door.

Inside the body 4

Piston Pushes the fluid along as the spring drives it back.
Rack The gear on the shaft turns in it and moves the piston.
Hydraulic fluid Has to squeeze past the valves, which slows the door.
Spring adjusting nut Turning it makes the door harder or easier to open and close.

The three valves 3

Sweep speed valve Controls closing until the door is nearly shut.
Latch speed valve Controls the last few degrees, so the latch catches.
Backcheck valve Cushions a door flung open, near the end of its swing.

Three mountings 4

Regular arm mount Body on the door's pull side. The arm stands out to the frame.
Top jamb mount Body on the frame, push side; the arm runs to the door.
Parallel arm mount Body on the door's push side. The arm folds flat under the frame.
Parallel arm bracket Holds the end of the arm on a parallel arm mount.

How this list was compiled: Read 2026-09-30; a name is kept only where two of these use it. (1) A door hardware maker's N900-PBF surface door closer installation instructions, https://cal-royal.com/api/media/file/Installation_Instructions_-_N900PBF_.pdf : closer body, main arm on the top pinion shaft, adjustable forearm and arm shoe, full cover, latch speed and closing (sweep) speed adjusting valves, back check control valve, spring power adjusting nut, parallel arm bracket, regular arm (pull side), top jamb (push side) and parallel arm (push side) mounting. (2) A second maker's TDC 70 installation instructions, https://www.townsteel.com/support/product-documents/tdc-70-installation : the same names for body, main arm, forearm, arm shoe, full cover, the speed adjusting valves, backcheck control, spring power adjusting nut and parallel bracket. (3) A third maker's 7100 series brochure, https://www.pdqlocks.com/hubfs/Website%20Content/Product%20Data/Door%20Closers/7100/7100-series-brochure.pdf : cast iron body, forged main arm, piston, full rack and pinion, cover, backcheck, and where the body and arm go in regular arm, top jamb and parallel arm mounting. (4) Yale rigid-parallel arm door closers PR1900 installation instructions (1980), https://archive.org/details/YaleRigidParallelArmDoorClosersPR1900PR1910PR1910F : main arm on the pinion shaft, spring power, sweep speed, latch speed and backcheck regulating valves, backcheck cushioning the door near the end of the opening cycle. (5) Door Closer Repair Manual, volume 1, Locksmith Ledger (1970), https://archive.org/details/door-closer-repair-manual-volume-1-locksmith-ledger : housing, spring, piston, hydraulic fluid, main shaft with a gear (pinion) that moves the piston along a rack, main arm, forearm and its foot, and how the trapped fluid slows the door. (6) Wikipedia, Door closer, https://en.wikipedia.org/wiki/Door_closer : the spring stores the energy of opening and releases it to close the door; sweep speed and latch speed; regular arm, parallel arm and top jamb surface mounting. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no maker's closer, nothing traced. Licence: own work

How it works

A door closer is a spring in a body of oil. Opening the door squeezes the spring; the spring shuts the door, and valves in the oil set how fast. Three views: on the door, cut open, and three mountings.

Read the full guide

What each valve sets

Sweep speed covers most of the swing shut. Latch speed covers the last few degrees, so the latch catches. Backcheck works the other way: it cushions the door near the end of its opening swing. The nut on the end of the body sets how hard the spring pushes.

Three ways to mount one closer

Regular arm: body on the door's pull side, arm out to a shoe on the frame. Top jamb: body on the frame, push side, arm to the door. Parallel arm: body on the door's push side, the arm folded flat on a bracket under the frame.

The pull side is the side where the hinges show. The push side is the side with the door stop.

Questions and answers

What are the parts of a door closer called?

Outside: the body under its cover, the main arm, the forearm and the arm shoe on the frame. Inside the body: a spring, a piston with a rack, the pinion shaft, hydraulic fluid, and the sweep, latch and backcheck valves.

How does a hydraulic door closer work?

Opening the door turns the arm and the pinion shaft, which moves the piston and squeezes the spring. When you let go, the spring pushes the piston back. The fluid has to pass the valves on the way, and that slows the door.

What do the valves on a door closer adjust?

Sweep speed is how fast the door closes for most of its swing. Latch speed is the last few degrees. Backcheck slows a door that is thrown open, near the end of the opening swing. A separate nut sets the spring's power.

What is the difference between regular arm, top jamb and parallel arm?

Where the body goes. Regular arm: on the door, pull side. Top jamb: on the frame above the door, push side. Parallel arm: on the door, push side, with the arm folded flat under the frame on a bracket.