"So many switches, so little time - Everything needs to be controlled, so here we take a look at all the various types of switches and how they function."
Switches of all types are used around your espresso machine to control different functions, from turning the machine mains on and off, to detecting pressure inside the boiler.
All switches on the espresso machine operate along the simple lines of the light switch in your house, either making a circuit or breaking a circuit, i.e. by allowing or disallowing the flow of electricity from one point to another, in order make some other machine component function.
Whilst there is a great variety of designs, they can be broken down into the following types and areas of operation:
Rocker Switch, Push Button - mainly used for machine on/off and beverage selection.
Rotary Switch - these are larger power handling and used mostly for machine on/off.
Microswitch - generally used for sensing that something has happened.
All switch designs do have a MTBF factor, Mean Time Between Failure, which means the switch is only designed to carry out a certain number of operations before it is expected to malfunction.
Normally the failure presents itself as the contacts inside the switch not making contact and making the circuit, simply fault finding using a meter is used for checking these types of fault.
Are available in either single or double versions and also with neon indication built in.
Image 2 shows the operation for this type of switch which is controlled by a ball rolling across a contact strip as the rocker switch is toggled from one position to the other, this action then transfers the circuit from the normally open condition to the normally closed condition.
Several designs are available, from single contacts to double contacts and also some switches that only make the circuit whilst you hold the button in, but the underlying working principle is the same in all designs.
As you push the button in, a set of contacts are broken and another set of contacts become made, changing the flow of the circuit from the normally closed to the normally open contacts.
Some switches act as momentary, meaning the circuit is only active whilst you are pressing button. Other buttons have a latching mechanism to hold the normally open circuit until you press the button again.
Rotary switches are larger than the rest of the switches shown here, due to the requirements to switch greater power that is required to run the full machine, they may also be able to switch not only single phase electricity but also 3 phase.
Operation wise, no circuit flows until the knob on the switch is rotated from the off to the on position, some machines will also employ a 2 stage rotary switch, the first stage only switches power to the control circuits, while the second position switches power through for the machines heating element.
Inside an espresso machine this type of switch will mainly be found on the smaller design pressure switches (slide 3).
Whilst outside the machine itself you will find this type employed a lot in your coffee grinder to detect if the grounds hopper is full.
Failure on most switches is normally down to the actual switch body breaking, making the cause of the fault pretty easy to spot and sort out. On rare occasions you may find that a contact inside the switch has failed and is found by testing the continuity of the contacts using a multimeter. When replacing any switch, remember to replace with like for like, and make a note/phots of any wiring.
Rotary switches which are found normally has the main power on/off switch on your machine, tend to fail when turning on due to stress on the cam arm inside the switch. Again using a multimeter will prove that the contacts have failed to switch correctly into the normally open selection.
