What makes an espresso machine a modern/hybrid lever?
- group head heated separately from boilers
- electronic control of when water flows to group
- pressure relief/shot stopper to end the shot when desired

This combination can make the modern hybrid lever work more like a modern saturated group espresso machine while keeping the essential characteristics of the classic lever espreso machine.

Here is a diagram showing how a hypothetical double boiler modern spring lever group espresso machine works. The Nurri, ACS, and others are likely to be similarly configured - I don't have access to any of them so I don't know for sure. The purpose of this is to describe how things can work and what is possible. Different machines may well have made different choices on how to provide similar capabilities.

The typical operation works by having movement of the lever and/or a manual switch trigger water flow into the group with a check valve holding the water in the group when the lever is released to allow the spring to start providing the shot pressure. When the shot is done a switch triggers the solenoid to release the pressure from the group and the water flows through an orifice that reduces the flow so that the lever doesn't move too flash and so it doesn't splash. Additional switches may be used to trigger water flow through the group or to the drip tray independantly of making a shot.



One innovative HB member came up with a method to modify a Strega to have a pressure release/shot stopper. Here is a diagram showing how I think a strega can be modified to operate similarly. The only changes required are adding the pressure release components. Here is a link: Bezzera Strega mods



Here is a diagram of BigEric's DIY Double Boiler Lever he recently built. While based on the hypothetical double boiler hybrid lever configuration it has further notable differences.

A gear pump controlled by a timer is used to control the volume of water being fed into the group cylinder. This allows for complete filling of the cylinder to ensure the largest possible shot volume and the highest possible spring pressure during the shot.

Incoming water is fed through a thermoblock to bring its temperature close to the brew boiler temperature then is fed into the brew boiler assembly which uses a coil wrapped around the boiler to dampen temperature fluctuations while the group cylinder fills. The volume of the boiler and preheat coil is sized to ensure that the water being fed into the full group cylinder is all the as close to the same temperature as possible.

An LSM group is used with modifications to initiate the timer when the group lever reaches the bottom of its travel. In addition, the internals of the preinfusion valve are removed to allow water flow to and from the group regardless of the position of the lever. The group head is heated by both cartridge heaters and a silicon band heater with a temperature sensor half-way up the group cylinder in order to reduce the temperature variations.



Here is a diagram of the current (and final?) configuration of my DIY Double Dipper Lever that now operates like a modern/hybrid lever. My goal was to be able to make each shot have the same temperature profile regardless of how much time had passed between the previous shot and the next. More specifcally, being able to make the next shot immediately after the prior shot with no temperature change has been my ultimate goal. There are some notable differences in my configuration.

Because the Condor group I used doesn't have a place for cartridge heaters I place them in a copper plate to which the group head is mounted. A band heater is installed around the group head bell to provide better heat control of the group head. I found that this was necessary to keep the group head temperature consistent from shot to shot. Without it the machine required an offset between the brew boiler and group head temperatures plus some amount of delay between shots for the group head to cool.

The brew boiler is fed by water from the steam boiler that has been mixed with line water to provide water that is a few degrees under the temperature of the brew boiler to ensure quick recovery without overshooting. This is done using the same mixing valve commonly used to control the temperature of the hot water tap on commercial espresso machines. The output of the mixing assembly goes into a preheat coil wound around the brew boiler then into the boiler to damp out changes in brew boiler temperature introduced by the incoming water. The volume of the brew boiler and preheat are sized such that a full cylinder's worth of water can be fed from the boiler/preheat coil combination. Without this the water filling the cylinder was not all at the same temperature and the group head temperature varied enough that it was necessary to temperature surf to get equivalent shot temperatures during back to back shots.

The dipper-stype Condor group has been modified by taking out the check valve ball and using a check valve in the line feeding the group from the brew boiler. In addition, the bottom two seals have been replaced by o-rings. This allows water to flow in and out of the group without pulling the lever because the only seal remains above the holes allowing water to fill the cylinder (just like the configuration of the LSM group). The o-rings fill the seal channels in the piston to reduce the amount of water required to fill the cylinder to a minimum.

A Matrix shower screen is used to prevent coffee solids from being allowed to reach the cylinder and piston when the pressure release solenoid is triggered.

A timer relay is used to keep the group fill solenoids just long enough to fill the group cylinder prior to releasing the lever. Because this is a dipper the preinfusion pressure is determined by the steam boiler temperature. Additional preinfusion pressure can be provided by controlling the raising of the lever when released.