Spring Piston Lever Espresso Machine A spring piston lever espresso machine is a "manual" espresso machine; that is, you, the user, provide the pressure needed to brew the espresso. These machines are different from normal piston lever machines in that instead of directly applying the pressure to water, the force of your arm is used to cock an internal spring inside the machines' grouphead. Once you release the lever, the spring pushes water through the bed of coffee at a steady, high pressure (approximately 8 to 9 BAR). Spring piston lever machines are capable of producing the best espresso possible when used by a seasoned veteran, by nature of the constant pressure they provide (as compared to the pulsing action of rotary or vibratory pumps). Machines in this class feature two different types of boilers. Dual switch machines maintain the boiler at brewing temperatures. Single switch machines maintain the boiler at steaming temperatures, but a heat sink design in the grouphead and the tubing between machine and grouphead reduce the temperature of the water that eventually is used to brew. The advantage of a single switch machine is that they can steam and brew at the same time. The disadvantage is that the machines can deliver brewing water that is too hot.