Concealed? Overhead? Hydraulic? Automatic? Door Closers Explained
Single vs Double Action
To understand different types of door closers you need to first be familiar with the concept of ‘single action’ or ‘double action’. A typical door would be single action in that it opens in one direction. A double action door is one that swings both ways and can open both inwards and outwards. ALL door closers (at least the spring-loaded ones we work on) are automatic.
Closures & Floor Springs
As a simple rule of thumb, what we would officially refer to as a ‘closure’ means an overhead closer for a single action door.
A ‘floor spring’ – also referred to as a concealed closer – would normally be for a double action door (because an overhead closer can only be fitted to one side of the door). We do occasionally see floor springs fitted to single action doors, but this is usually not necessary.
A door closer is fitted to the top of the door on the hinge side, whereas a floor spring is a box that sits in the floor underneath the door, often concealed from view.
The size of any door closer or floor spring is related to the size and weight of the door.
A cam-driven closer has gears inside instead of a spring. The gears will turn only so far – that is, up to a certain force in Newtons (which is adjustable) as the door is opened. When the door is no longer pushed or pulled the gears then turn back to close the door.
Overhead (Transom) Closers & Closures
An overhead closure has a drive arm that pushes the door closed. Depending on the layout of building and the door, there might be a slide rail (for when the arm needs to be recessed).
A ‘transom’ closer is just another way of saying ‘overhead’. It takes the form of a pivot connected to a drive arm: the arm is bolted to the top of the door, with the other end of the closer attached to the top of the door frame. When the door is opened the oil inside the closer is put under pressure, and it is this pressure that slowly pushes the door closed when it is no longer being held open.
All door closures and door springs are hydraulic and filled with oil. We have come across some pneumatic floor springs which used ‘air checks’ and had a rubber plunger on the check cylinder, but these springs were discontinued in the 1930s so finding one now is very rare indeed!
How Door Closers Work
All door closers and floor springs must first be pushed or pulled open. This opens the coil spring, which wants to close. It is the coil spring that closes the door automatically using hydraulic oil pressure.
On good quality door springs and closers the oil pressure can be adjusted to change the ‘response’ of the door to being opened, and therefore the speed at which it closes again.
Top Centre Set
A top centre set is fitted to the top of the door and the top of the door frame, and holds them together via a spindle (a rod or pin that is the axis for the door’s rotation). We’ve always found it amazing that some makes (Modric and Jebron to name two) have a spindle the size of a little finger yet are often specified for big doors with a huge load by architects.
Bottom Shoe / Shoe Strap
As the name suggests, a bottom shoe or shoe strap holds the bottom of the door onto a floor spring pivot. Both are required to close the door.
An EMB is a floor spring or door closure which has an electric solenoid built into its body to connect it to the fire alarm system and to keep it permanently open as long as electric current flows through the solenoid. Should the fire alarm go off, power to the door is cut, and the closer then operates like any other. The door can still be opened but, if not held open, it will close to prevent the spread of fire and smoke.