Understanding Preload

What is PRELOAD?

Simply stated, door preload is pressure exerted on a door and in turn transferred to the keeper of the electric strike by the latch.

When pressure is applied to some models of electric strikes, the solenoid may not have the ability to mechanically release the keeper because the pressure binds it against the latch.

Even a small amount of this preload can cause problems in the functioning of some electric strikes. Door preload can prevent the smooth unlocking of the electric strike or even disable a strike – preventing a door from being opened.

Why is it IMPORTANT?

Failure to release can prevent a door form opening, hindering safe passage or egress which could create a life-safety issue.

Additionally, a door left unlocked by a faulty electric strike leaves a building vulnerable.

What CAUSES Preload?

A number of conditions can cause door preload including:

Stack pressure caused by HVAC systems
Misaligned strike and lockset
Warped wood doors; Damaged or bent metal doors
Thick door seals or heavy weatherstripping

A strike that does not open or opens only intermittently could be showing signs of a preload problem. If preload pressure causes a strike or multiple strikes to malfunction, many access and security issues arise.

Common SIGNS of Preload

What to watch out for:

Markings on the strike plate by which the latch is rubbing when the door is closed
Door marks on the frame where the door is rubbing due to tight clearance
Door skin loosening due to excessive force and wear and tear on the door
Excessive paint chipping near the frame strike or on the door latch areas]

Preload & Building Security

An electric strike failing to release when energized is not the only problem preload can cause.

If the power to the electric strike is interrupted, either by accidental or deliberate means, strong preload pressure can cause a strike in fail safe mode not to function.
If a serious preload condition is present when the strike is activated the pressure will move the door slightly into an open position, leaving the door unlocked, and the building vulnerable.
Some of the underlying problems that cause door preload, such as pressure from air conditioning, are not practically or easily corrected.

Adams Rite electric strikes to address preload:

7400/7401 Series

Preload capable and outdoor rated. Works with Adams Rite 4500 and 4900 Series deadlatches and other cylindrical locksets with 1/2" to 5/8" latchbolt projection.
74R1 | 74R2

Preload capable and outdoor rated. Works with Adams Rite Rim Exit Devices with Pullman Latchbolts.

Additonal Resources:

Preload & the Ultraline Solution Brochure

Related Training

Understanding Electric Strike Selection

Related Training

Troubleshooting Electric Strikes