It combines the bottom pivot and the door closer in one buried unit.

The door closes itself with nothing visible above the floor.

That suits frameless glazed entrances where an overhead closer would intrude.

It controls closing speed and provides latching action.

Most offer a hold-open position as well.

On a double-acting door it controls both directions and returns the leaf to centre.

By balancing reliable latching against the force needed to open the door.

The door must close against draught and latch properly.

It must also be openable by the people who use it.

Accessibility requirements set maximum opening forces in most markets.

An entrance adjusted hard enough to always latch can be unusable.

Where they conflict, the accessibility requirement generally prevails.

That usually points to a power-operated door rather than a stronger spring.

Increasing force to force latching defeats the accessibility requirement.

Draught, air pressure and seals are worth addressing first.

Latching action at the end of the swing can be adjusted separately.

A badly aligned keep is a common underlying cause.

Automatic operators resolve the conflict where the building genuinely needs both.

A cement case set into the floor at construction, level and correctly positioned.

Position has to be accurate relative to the finished opening.

Drainage provision matters at external doors.

Water in a floor spring is a common cause of entrance failures.

External installations need the drained version.

Retrofitting into a finished floor means cutting it, which is not always possible.

By lifting the door off and removing the cover plate.

That is considerably more work than adjusting an overhead closer.

Replacing the unit means opening the floor again.

Lifting a glass door needs proper equipment rather than improvisation.

It is the honest disadvantage of the whole arrangement.

Specifying a quality unit at the outset matters more here than almost anywhere in door hardware.

Not on fire doors, which must close under all circumstances.

Hold-open on a fire door defeats its purpose.

Electromagnetic hold-open devices that release on alarm are the compliant route.

Those are specified and tested as part of the fire strategy.

Requirements differ between markets and are enforced.

A mechanical hold-open on a fire door is a serious defect rather than a preference.

Water ingress, grit and hydraulic seal wear.

Entrances collect both water and grit continuously.

Seal wear shows as the door slamming or failing to close.

Oil leaking into the case is a sign the unit is finished.

Adjustment can mask early symptoms for a while.

Given the work involved in replacement, keeping the cover plate sealed and the area drained repays itself.