What a floor spring does
A floor spring is a heavy hydraulic mechanism sealed in a steel cassette and buried flush with the floor immediately under the door. It performs two jobs at once: it carries the weight of the door (replacing the bottom pivot in this arrangement), and it controls the door's self-closing action through a hydraulic damper. Floor springs are the standard choice on heavy commercial entrance doors, glazed automatic-converted doors, and any door where a transom closer would spoil the visual line at the top of the frame.
The cassette runs on filtered hydraulic oil. Two sets of seals keep that oil in: one set around the moving spindle that the door rotates on, and another set around the cassette body where it joins the cover plate. Both sets wear. When they fail, the oil escapes — onto the threshold first, then into the floor below.
How a leak progresses
The first sign is a dark stain on the threshold immediately adjacent to the spindle. It is easy to mistake for general grime on a busy entrance, which is why retail and hospitality customers often spot it only when a cleaner reports the stain coming back after every mop. The stain is followed within a week or two by visible droplets accumulating in the corner of the cover plate. At that point the cassette has lost enough fluid to start affecting the closing action.
As oil escapes, the cassette's closing pressure drops. The door slows in the last few degrees, stops short of the strike, and the latch will no longer engage on its own. Customers describe it as "the door not closing properly" — but the underlying fault is mechanical, not adjustment. Cranking the closing-speed valve will not bring back hydraulic pressure that has leaked away.
The failure mode after the leak
Two things can happen once the cassette has lost most of its fluid. Either it seizes — the air bubble in the body causes the valves to cavitate and the spindle stops rotating freely — and the door slams home with full unchecked spring force on every cycle. Or the spindle binds in its bearings and the door becomes physically heavy to open. The first failure is dangerous because the slam shock-loads the glazing and the corner joints. The second is dangerous because users start propping the door open, defeating fire and security functions.
Either way, the cassette is at the end of its life. Floor springs are not field-serviceable. The cassette body is welded shut around the spring stack; even where access is possible, the working tolerances are too fine for in-situ refilling. The only repair is to lift the cover plate, remove the cassette, and replace it with a new one.
The replacement work
A standard floor spring replacement runs to half a day on site. The door is removed and stored against the wall. The cover plate is unbolted. The cassette is lifted out of its pocket — this is the heaviest part of the job; a single-action floor spring weighs 8–12 kg. The pocket is cleaned of accumulated oil and debris. The new cassette is dropped in, levelled, and bolted down. The door is reset onto the spindle, the latch adjusted, and the closing speeds tuned. Finally, a fresh threshold seal goes on around the cassette to keep moisture out of the pocket.
See commercial floor spring repair for the full service description. Cover plate repair is a separate, lower-cost job when the spring itself is sound but the cover plate has lifted or corroded.
Brands and stock
The UK commercial market is dominated by four floor-spring brands: Dorma, Geze, Vachette and Brimar. We carry universal-fit cassettes that retro-fit the large majority of installed pockets, plus brand-specific cassettes for Dorma BTS and Geze TS-500 systems where a precise direct replacement is required. On a same-day quote we ask which brand is on the cover plate or, if the plate is unbranded, which closer brand is fitted on other doors in the building — they are usually the same.
For multi-site customers, we keep a register of which floor springs are fitted where so a fresh callout starts with the right cassette already on the van.
Preventing premature failure
Floor springs designed for moderate-traffic commercial entrances are rated for 500,000–1,000,000 cycles. A high-traffic retail or hospitality door can clock that in 3–5 years; a moderate-traffic office entrance takes 8–10. The single biggest determinant of how close to the rated life a given cassette reaches is whether the closing speeds are kept correctly adjusted. A floor spring that has been allowed to slam, or to drag against a misaligned strike, ages 3–4 times faster than one that is checked and tuned every six months.
A standard floor spring service contract covers the six-monthly adjustment, threshold inspection and leak check. For full-stack cover see commercial door maintenance.