Espresso Machine Water Pump Systems
by Terry Ziniewicz
Fresh Cup Techno-Jolt Archive - March 2000

Introducing this month's Techno-Jolt, another informative narrative on the inner workings of espresso machines and related devices.  This month I'm going to tackle the topic of espresso machine water pumps.

All espresso machines require some type of hydraulic force to create the pressures necessary to extract espresso.  Most modern espresso machines rely on an internal or external electric pump to build this pressure.  This pump machine replaced the older lever machine, which required the barista to pull a lever to create the necessary pressure.  This is where we get the term "pulling a shot."

Electric pumps have not only made it easier to pull shots, but they've also provided a more consistent method of creating pressure.  This, in turn, has resulted in a more consistent method of extracting espresso.

The type of pump found in most commercial-quality espresso machines is a rotary vane pump.  This pump is made of two pieces - a brass rotary vane pump head and an electric motor to turn the pump.  The brass pump head is attached to the electric motor by a clamp or bolted flange.  The placement of this pump varies by manufacturer and age of machine, so in some cases, the pump assembly will be external.  Most current machines, however, have an internal pump assembly, and in some cases, the electric motor will be water-cooled.  This type of pump created the most reliable form of group head pressure. 

Rotary vane pumps are adjustable.  It's necessary to adjust the pump to create the desired pressure at the group head.  Adjustment is made by way of a screw found on the brass portion of the assembly.  A clockwise adjustment will increase pressure, while a counterclockwise adjustment will decrease pressure.

Inlet pressure is also accounted for in this adjustment, so when installing our machine, make sure the inlet pressure is less than two bars.  If inlet pressure is higher than this, you should install a Watts-type water regulator to decrease it.

When a rotary vane pump starts to fail, one telltale sign will be an overly active pressure gauge.  When you are pulling a shot, watch the gauge; if it is dancing around, there's a good chance the pump needs to be replaced.  Other signs that your pump may be bad are low pressure at the group head and a lack of adjustability. 

The reason most rotary pumps fail is a lack of water.  Even if the pump runs dry for only a moment, it may be damaging.  You should never let an espresso machine with a rotary vane pump draw water from a water tank or a non-pressurized water source, because it will only increase the chance of damaging the pump.  Rotary vane pumps require a pressurized water source to work properly.

If you need to use your machine where a pressurized source of water is not available - such as in a catering situation or at a trade show - be certain to use an external diaphragm pump.  These are manufactured by a number of companies, and they ensure you will be providing the correct inlet pressure to your machine.

If you have a water filtration system in place, make sure it's in good working order, as the water pressure can dissipate over time.  Filtration systems can easily become clogged with the debris you are trying to remove from the water.  If a filter reduces water flow, this can also cause potential damage to the water pump.

The second most common type of pump is usually found on most high-end home and semi-commercial espresso machines: the vibratory pump.  Vibratory pumps will most always be located internally and are one-piece, non-serviceable devices.

Given that they are never allowed to run dry, vibratory pumps can and do provide a reliable form of pressure to the group head in a low-volume environment.  Although this pump is self-priming and can be used to draw water from a non-pressurized water source, vibratory pumps cannot handle continuous repeated use, as the temperature of the pump body rises quickly and can cause premature failure.

These pumps are not adjustable unless the manufacturer has installed some form of water regulator on the outlet side of the pump.  Generally, the rotary vane pump is better suited for high-volume espresso extraction.

As we continue to explore the inner workings of the espresso machine, it is important to remember you should only complete repair and maintenance that you are confident and comfortable with.  Always remember to use caution when working on your equipment, and when in doubt, call your local technician to complete the job or to answer any questions.

Disclaimer:  I am in no way a water pump expert.  My knowledge comes from personal experience and having lovingly worked on hundreds of espresso machines.  If there is more to this story, please let me know.  Until then, create good coffee karma and hug your espresso machine every day.