Last Updated on February 21, 2023
Door closers operate by balancing two forces. The first force is a spring, which wants to pull the door back into a closed position. Hydraulic fluid, the counter force, is used to dampen the motion of the spring and prevent slamming.
The Purpose the Spring
The spring in a door closer acts to pull the door closed. By itself, it accomplishes the goal, however by itself it would also result in the door getting slammed into the frame with excessive force, inflicting damage to the door, the frame, the locks, or any fingers that may be in the way!
To balance this force, and prevent the door closer from slamming shut, a system of hydraulics is used.
What is Door Closer Fluid
Inside a door closer there are chambers filled with hydraulic fluid.
When the door is opened, a check valve opens that allows the closer fluid to rush into a far chamber with practically no resistance at all. Very quickly.
But for the door to close, the fluid needs to return back to it’s starting chamber. The initial check valve won’t let the fluid return back the way it came in; instead, the fluid must navigate through restricted chambers or tubing, with much smaller openings.
The Function of Door Closer Fluid
Restricting the “back flow” of the hydraulic oil slows the movement of the fluid and thus, slows the door closing speed, allowing it to close at a speed which is much more delicate on the entire door assembly.
So to adjust the door closing speed, you are adjusting how fast the fluid can return to the original chamber.
This basic method has been used in door closers for over 100 years. While it is a simple concept, various adaptations to the principles allow for additional door closer features which have uses in different applications. Whether you have a very basic or a very complex model, they are designed so you can adjust a door closer for optimal performance.
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