How Does a Bialetti Pressure Valve Work?

Coffee maker machines brew coffee by boiling water to such a high temperature that the pressure of the steam (gaseous water) forces the water up an outlet pipe and through the coffee grinds and filter.

Because the amount of solids that water can dissolve increases with temperature, the boiling water can quickly absorb the coffee's flavour particles. The liquid below is coffee or espresso, depending on the quantity of beans used.

How Coffee Maker Pressure Valves Work

High steam pressure is necessary to brew coffee. However, if there is a problem with the outlet pipe, then the pressure can't escape, building to potentially explosive levels. As a safety feature, the water heating reservoir is attached to a pressure valve calibrated to release pent-up steam if the internal pressure exceeds a certain level.

These pressure valves use one of two mechanisms: a ball seal and a helical-spring-with-plunger seal. The ball is made of a dense metal and sits inside a cylinder where it covers a small opening. The weight of the ball is such that when the steam pressure reaches a dangerous level, the resulting force is strong enough to temporarily lift the ball and escape.

A spring valve consists of a spring forcing a plastic plunger into a hole below. Once the pressure reaches a certain point, its force will overpower the spring's, lifting the plunger and escaping.

How A Bialetti Mukka Pressure Valve Works

The Bialetti Mukka's patented design has more to do with its cost-saving manufacturing process then its mechanism. Basically, the Bialetti Mukka Pressure Valve is a typical sping-and-plunger valve. The difference has to do with the way the spring is secured. In other spring-and-plunger models, the valve casing is cup with a flat edge. The spring itself extends beyond this open end a few millimetres. To "load" the spring, a separate cap would be screwed/welded/attached to end, compressing the spring inside.

The Mukka design uses an extra long cup, so that the spring doesn't extend beyond the edge. Then, a machine squeezes the end of the cup into a round opening called a "die," which folds the first few millimetres of the cup's edge over, forming an overhanging lip around the inside. In turn, this lip compresses the spring inside the cup, loading it with tension.

So, the Bialetti company doesn't have to manufacture a cup or pay a worker to attach it. In this sense, the true value of the patent lies in giving Bialetti the right to protect the competitive edge granted by its own ingenuity.