When should I use a rack and pinion closer?

When should I use a rack and pinion closer?

Door closers tend to use two mechanisms to apply the force required to open a door: rack and pinion and Cam action. We’re often asked about the difference between the two. In this blog we’re going to look in more detail at rack and pinion door closers, often called scissor arm or articulated arm closers.

A rack and pinion door closer is one of the most widely used types of door closer, and is so called because it uses a rack and pinion mechanism with a spring(s) to provide power to close the door, and hydraulics to control the speed of the door closure. As the door is opened, the pinion rotates, forcing the rack to move and compress the spring(s), storing energy to close the door. This guarantees exceptional ease of use by reducing the resistance encountered when opening the door. It is a great choice for public, residential and commercial applications.

There are some instances where a rack and pinion door closer might be the preferred option:

Reverse shoe trick

Door closers sometimes have to be adjusted in buildings where air pressures affect the ability of the door to close. This might be in an exit stairwell where air pressure extremes can be at their most acute, or it could be in a hospital where positive air pressure is deliberately maintained in operating theatres as an infection control measure. 

Rack and pinion and Cam action closers can both be power adjusted in these scenarios, and often that will resolve the issue so that the door closes fully and reliably. However, if it doesn’t, the rack and pinion closer has an additional trick up its sleeve. The shoe on the triangular bracket on the arm is slightly offset so that it can be installed with the shoe reversed to make the angle of the arm more acute – this increases the output on the latch, ensuring that the door closes. 

This neat trick can also be used where smoke, noise or draught seals have been added to the door but have subsequently increased the friction when the door closes, or if the design of the latch requires a bit more force to click shut.

Opening angles

The other instance where rack and pinion closers might be the preferred option is where an opening angle of 180 degrees must be achieved. For example, in hospital corridors where it is vital to ensure there are no obstructions, a door is required to open and sit flat against the wall. A rack and pinion closer can do this, whereas the opening angle of a Cam action closer is restricted to 110-120 degrees, which would mean the door would obstruct the corridor.

Things to bear in mind

One thing to note is that when rack and pinion door closers are fitted on the push-side of a fire door, they lose a power size. This is significant where seals are being used to mitigate smoke risk, as the friction caused by those seals could make the difference between the door closing or not. This issue has been cropping up more frequently since the Grenfell enquiry due to increased insistence on 3mm door gaps and the use of smoke seals to protect life safety. 

For this reason, in this scenario we advise principal designers and building owners to specify the maximum power adjustable door closers they can afford, especially for apartment doors which open into airlocks and small sealed rooms. Starting with a power adjustable EN 2-5 closer is best practice and will also help to avoid costly callouts to site and potentially having to change closers. Incidentally, we have seen instances where fire doors with retro-fitted closers have been condemned by fire inspectors because the excess holes in the top have affected fire integrity, so it’s best to avoid this by specifying a door closer that is definitely up to the job.

We hope this ‘close up’ of rack and pinion closers is useful. You can see our full range here, and please contact us if you have any further questions – we’d be happy to discuss in detail.