The following is a brief description of espresso machine water pumps and the procedure on how to adjust the dispensing pressure.

All espresso machines require water. Water can be supplied to espresso machines in a number of ways, and most commercial machines require pressurized water in order to function correctly and attain optimal results. Pressurized water is required especially in the case where a rotary vane water pump is used. These are the types of pumps used in 99.9% of commercial espresso machines today.

There are various different styles of pumps. In most instances a clasp attaches the pump to a motor. In other cases there may be two or three bolts holding the pump and motor together. Some manufactures do not assemble their equipment with the pump and motor inside the case of the espresso machine, so the pump and motor are found underneath the equipment.

All pumps are adjustable, but may have different looking adjustment screws on the mechanism, called the "by-pass valve", depending on the pump manufacture. These are always located on the side of the pump, and are usually only accessible by removing the body panel closest to the pump and motor (except in the cases where they are found outside the machine). It should be noted that manufactures do not necessarily use the exact same make and model of pump on every piece of equipment that they sell, and, depending on supply, a different version pump may be found on two machines that are in all other ways exactly the same.

The owner and user of the equipment should always know where the pump is located, and it is highly recommended to have a spare on hand, in the event of pump failure. A gradual loss of water pressure, manifested by slow dispensing times and a very low reading on the pressure gauge (lower than 9 bar or optimal pressure previously set) while dispensing is indicative of a pump failure. The complete loss of any pressure whatsoever may also indicate a pump failure, but is more likely the motor or start capacitor on the motor that has failed (after confirming water at 20psi is being supplied to the pump).

Adjusting the pump pressure is simple. It is important to note two things only:
  • there is water supplied to the pump at a minimum of 20psi to a maximum of 60psi, and
  • water is dispensing out of one of the group heads

While water is dispensing out of the group head, turn the adjustment screw on the by-pass valve clock-wise to increase the pressure and counter clock-wise to decrease the pressure. 9 bar is a standard acceptable pressure for brewing espresso, but is by no means exact for every manufacture. The pressure at the group head and the pressure at the gauge can and do vary in most cases, due to their proximity to the pump as well as expansion valves in the hydraulic system of the equipment. Use 9 bar as a starting point and adjust accordingly to the shot time and volume that best suits your taste.