A Tap Is A Cartridge With A Body Around It

A tap presents as a solid metal object and functions as a housing for one small replaceable component. The cartridge does the sealing, the mixing and the flow control, and it is where nearly all failures occur.

Ceramic discs replaced rubber washers

Traditional taps sealed by screwing a rubber washer down onto a seat, and the washer compressed, hardened and eventually leaked, which is why they needed regular attention.

Ceramic disc cartridges use two polished plates that slide across each other, sealing by the flatness of the surfaces rather than by squeezing a soft material.

Because nothing is being compressed, the mechanism has no wearing element in normal use, and a quarter turn moves it from closed to fully open.

Grit is what actually kills a cartridge

The sealing depends on two very flat surfaces staying in contact, so any hard particle carried in the water becomes a scratch across the sealing face.

A scratched disc leaks continuously, and the drip that follows is usually blamed on the tap as a whole rather than on a component costing a fraction of it.

Debris from pipework disturbed during installation is the commonest source, which is why new taps sometimes drip within weeks and why flushing the supply before fitting matters.

A mixer blends by proportion, not by temperature

A single-lever mixer opens the hot and cold ports in a ratio set by the lever position, so the temperature produced depends on the supply temperatures at that moment.

If either supply pressure changes, the ratio delivered changes with it, which is the mechanism behind a shower running hot when a tap elsewhere is turned off.

Thermostatic cartridges add a temperature-sensitive element that moves to maintain a set outlet temperature, which is a genuinely different device rather than a better mixer.

Pressure and flow requirements are part of the specification

Taps have a minimum pressure at which their internal restrictions still deliver useful flow, and a low-pressure gravity system may not meet it.

Aerators at the outlet mix air into the stream to make a modest flow feel fuller, and they also clog with scale, which produces the familiar gradual loss of flow.

Flow limiters fitted for water efficiency sit in the same place, so what feels like a failing tap is often a small insert that can be cleaned or removed.

Finish and body decide the long-term appearance

Bodies are usually cast brass, which is chosen for corrosion resistance and machinability rather than strength, and it rarely fails structurally.

Chrome plating is thin and durable but shows damage permanently, while brushed and coated finishes hide marks better and are more vulnerable to abrasive cleaners.

Since the mechanism is replaceable and the body is not, the sensible durability question about a tap is whether its particular cartridge is a standard, available part.