The ability to make good espresso is one of the most coveted skills in the coffee world. The rich body and complex flavor profile of a well-made shot brings the beans to life with a depth that other brewing methods fail to achieve. But espresso is also among the more complicated ways to make coffee. Fine grinds, high pressures, short brew times, metered doses, and precise temperatures all work together to create the perfect shot – but a variation in any one of these variables can just as easily render it undrinkable. Making consistently good espresso requires consistent brewing parameters.

Unfortunately, traditional consumer-grade espresso machines are not very good at keeping water temperature consistent. They typically manage the boiler temperature with thermal cutoff switches, which have a large temperature range, switching off the heater when the temperature reaches the top of the range, and switching back on when it gets to the bottom of the range. This can result in temperature swing of 10°C or more, but espresso requires a precision of at least 1°C for reliable results. Because of this, many home baristas will learn to “temperature surf” by measuring the boiler temperature at various points in the heating cycle and tracking the time after the thermal cutoff switch turns off to hit their desired brew temperature. This technique is very tedious to execute correctly and is subject to variations in individual machines and environmental conditions.

The best way to keep the boiler temperature consistent is by implementing a PID control algorithm, which is designed to optimally regulate temperature and can easily achieve sub-degree accuracy. There are many commercial PID controllers available on the market, but they each have drawbacks such as size, cost, and customizability. To overcome these hurdles and create a solution that meets our temperature control needs, Protofusion has developed a tiny open-source PID controller called Therm.

Therm uses a thermocouple to measure temperature and has a digital output that can be paired with a solid state relay (SSR) to control heating elements or other thermal devices. Because the software is open source, it is easy to add new parameters, control strategies, and features. For this project, we will use Therm to control the boiler temperature of the Gaggia Classic espresso machine and configure the software to read in the state of the switches on the front of the machine to select between brew and steam temperatures. This seamless integration will preserve the existing machine interface and aesthetic while providing the benefits of precise and stable PID-controlled boiler temperatures.

Start to finish, it took me about 2 hours to complete this project. I would imagine the whole thing could be achieved in an afternoon by anyone comfortable around tools and with basic soldering experience.

Schematics

Above is the schematic and wiring diagram for an unmodified Gaggia Classic machine. This is the starting point for the modifications we’ll make, and we’ll try to leave as much of the system as possible undisturbed. In fact, if you follow the directions here, it should be very easy to revert the machine back to the stock configuration.

The first addition to the system is a Therm module to act as the new brains of the machine. Therm runs on a 5V power supply, which doesn’t exist in the stock machine, so we’ll need to add that too. To measure the temperature of the boiler, we’ll need to add a thermocouple. We also want to remove the old thermal cutoff switch that was used to control the brew temperature. Physically removing the cutoff switch is not strictly required, but it leaves a nice place to install the thermocouple, so I would recommend it. Either way, we’ll want to take it out of the circuit and replace it with a solid state relay. The SSR will turn on and off to regulate the temperature just like the cutoff switch did, but it will be controlled by Therm rather than a mechanical thermal mechanism.

Next, we need a way to tell Therm whether the machine is in brew mode or steam mode, so it can set the temperature setpoint accordingly. In the stock machine, the steam selector switch on the front panel is used to bypass the brew cutoff switch, which will allow the temperature to go up to the limit imposed by the steam cutoff switch. But now, we want Therm to control the temperatures and not the cutoff switches. To do that, we’ll disconnect the steam selector switch from the cutoff switch, and instead, connect it to an input on Therm.

I decided to leave in the steam cutoff switch because it will help protect the boiler from getting too hot. The machine also has a thermal fuse that will trigger if everything else fails, but since it is a single-use fuse, I didn’t want to risk blowing it while I was tuning my Therm settings. I did, however, decide to upgrade my steam cutoff switch with a 155°C replacement, which should help the machine deliver a larger volume of steam from the boiler compared to the stock 145°C cutoff. This upgrade is completely optional as it doesn’t directly influence the PID control system, but it may be worth considering since you already have the machine open.

Below is an updated schematic which shows all of the changes we want to make to the system. Next, we’ll look at the specific parts we’ll need and then go through each step required to complete the modification.

Parts List

Therm: Therm is a open source PID temperature controller created by Protofusion. Unfortunately, it is not currently available for sale, but since it’s completely open source, you’re welcome to download the design files and fabricate one yourself!

Solid State Relay: SSRs can be cheaply sourced from places like eBay, but be careful not to skimp on this part. The Gaggia Classic has a max power consumption of more than 1400W, which can easily burn up a cheap SSR. If the brand or source is questionable, I would recommend derating the current by a factor of 2 or 3 and going for a model rated for 25-40A just to be safe.

Thermocouple: Thermocouples are used to precisely measure temperature. They come in all shapes and sizes for many different applications and can have a wide range of price points. Fortunately, several popular low-cost 3D printers use a thermocouple with an M4 thread that perfectly matches the thread of the thermal cutoff switch we are removing, making it easy to find and a perfect drop in replacement for this modification.

Power Supply: The Therm PID temperature controller needs a 5V power supply, but the only power available in the stock machine is 120V AC. Just about any AC to 5V power supply will work, since Therm doesn’t consume much power, but I chose this MeanWell module for its low cost, small form factor, and easy connection points. A basic USB phone charger would also work well if you have an old one laying around.

High Temp Wire: Wire rated for high temperatures is a good idea for this modification because the inside of an espresso machine can get hot enough to melt standard wire insulation. I chose wire with silicone insulation and a 200°C rating. You’ll need some relatively heavy gauge wire for wiring the heaters, but the signal wires for the SSR control and steam selection switch can be much smaller. I used 16 gauge wire for the high power lines and 22 gauge wire in red, blue, and black for the low power circuits.

Spade Connectors: Spade-style quick connect terminals are used in the stock espresso machine wiring, and it’s nice to be able to plug the new circuit additions directly into the existing harness connectors. This isn’t strictly required, and there are plenty of other ways to create electrical connections, including splices, solder joints, and different connector styles.

Thermal Paste: Thermal paste is used to improve heat transfer. In this case, we want temperature changes in the boiler to influence the thermocouple as quickly as possible. While not absolutely necessary, a dab of thermal paste will help to improve the accuracy and response time of the temperature measurements. (Any old thermal paste will work well – Arctic Silver is definitely overkill, but it’s what I had on hand.)

155°C Thermal Cutoff Switch (Optional): The stock machine comes with a 145°C thermal cutoff switch for steam temperature, which restricts the amount of steam that can be made in the small boiler. Upgrading to a 155°C cutoff should significantly improve the available steam volume.

Required Tools

• Screw drivers
  
• Adjustable wrench or wrench set
• Wire cutters
• Crimpers or pliers
• Soldering iron
  
  

Detailed Steps

Here are more detailed instructions on making the modifications step by step:

1. Open up the machine: Remove the two screws along the back of the top cover and take off the cover, along with the water funnel.
2. Remove brew cutoff switch: The brew thermal cutoff switch is located on the side of the boiler, opposite the steam knob. It’s threaded into a mounting hole and you might see some some white/gray thermal paste coming out around the edges. Disconnect the spade connectors plugged into it, and use a wrench to back it out.
3. Install thermocouple: The thermocouple in the parts list has an M4 thread to match the cutoff switch thread, so installing the thermocouple is as easy as screwing it into the open hole. A bit of thermal paste on the tip before installing is recommended, but not required, especially if there’s lots of thermal paste left from old switch.
4. Replace steam cutoff switch (optional): If you opted to upgrade the steam thermal cutoff switch, you can swap that out now. The steam cutoff is found on the top of the boiler, and looks just like the brew switch. Make sure you reconnect the wires once the new device is installed.
5. Disconnect steam switch on front panel: The steam switch is double pole, which means it has two separate circuits running through it. We only want to disconnect the side that goes to the heater coil, which is the side closer to the brew switch. Disconnect both the top and bottom connectors. In my machine, the top connector had two gray wires and the bottom one had a single blue wire.
6. Wire up and connect SSR: Use the heavy gauge wire to add leads to the SSR output side and terminate them with male spade connectors. Since the SSR takes the place of the front panel steam switch in this circuit, we’ll want to connect the output directly to the wires we just unplugged from the front switch. Plug the male spades into the female connectors from the front panel switch. Add wires (thinner wire is fine) to the SSR +/- input to connect to Therm.
7. Wire up power supply: The 5V power supply needs to connect to the AC power coming into the machine, preferably after the power switch. For the AC hot connection, I used the connectors that were unplugged from the brew thermal cutoff switch (on mine, the hot side had a single gray wire). For the neutral connection, I spliced a wire with a connector into the neutral line going out to the power plug. Wire up the power supply and connect the AC hot/neutral to the machine, leaving 5V wires ready to connect to Therm.
8. Wire up and install Therm: Use female spade connectors and the thinner wire to connect the front panel steam selection switch to the Therm aux pins. Also connect the thermocouple, SSR input, and 5V lines to the matching Therm ports. I used ferrules to terminate the wires going to the Therm screw terminals, but bare wires would also work just fine.
9. Reassemble the machine: Double check that all of the wires are hooked up, and then replace the top cover and the water funnel, along with the screws that were removed during disassembly.

Conclusion

You’ll be amazed at how consistent the Gaggia Classic can be in creating repeatable shots when the boiler temperature is stable. PID temperature control allows you to focus on the art of pulling a good shot, instead of constantly worrying about fluctuating brew temperatures.

I recently purchased a used Gaggia Classic machine on Amazon. After realizing that it was not as “lightly used” as the seller denoted, I took apart the entire machine to clean it up. I’ve written this guide as a teardown guide, but feel free to read it from bottom-up to get a clear understanding of how to assemble this machine. Feel free to drop a comment if you have any questions or information to add.

Tools

Before you start out, I would recommend purchasing a few tools (most available at your local hardware store):

• Brass brush
• Metric allen wrench set
• Citric acid or espresso machine cleaner
• Phillips screwdrivers
• Pliers or a crescent wrench

Note: You can buy citric acid at many bulk food stores for a reasonable price

Remove the Boiler

Begin by removing the two attachment screws on the top of the machine by the water spout. The top plastic water spout / sheet metal assembly should pull off towards the back of the machine.

Next, pull the steam wand knob off (it might take a bit of effort). Note that the valve in the photo above is a bit offset, this is due to my machine being damaged. Yours should (hopefully) be centered in the hole. You’ll also want to pull the push-on connectors off of the power connector on the rear of the machine, and pull all the cables off of the front switch. I recommend numbering each of these connectors before pulling them off so you can easily reconnect them.

Flip the machine over and use allen wrenches to remove the four bolts attaching the group to the chassis.

After removing these screws, your boiler should be free. Remove the boiler from the chassis and place it in a clean work area. Note that things might get messy and/or moist very soon.

Using a standard or crescent wrench, remove the chromed steam wand from the copper steam pipe. This will allow you to set the group down on a flat surface without damaging the copper pipe.

Next, detach the electronics and pump from the machine. You will need to detach the pump hose from the OPV and unplug all push-on connectors. If you leave your wire assembly as-is after you unplug all connectors (don’t bend or crush the wires!) you should be able to easily see where all of the wires connected to for reassembly.

To make life easier, remove all hoses from the machine. You should only need to remove the 3-way solenoid hose and the OPV hose at this point.

Now flip the boiler on its side. You’ll see a phillips screw head in the middle of the shower screen.

Remove the phillips screw from the shower screen, and then pull off the shower screen itself. If it is stuck due to calcification or coagulated coffee compounds, use a small flathead screwdriver to pry it off.

Now grab an allen wrench and take off the metal block that resides under the shower head. You should now be able to see the top of the group.

Using a plastic spudge, flathead screwdriver, or even your fingernails, carefully pry up the rubber gasket from inside the group.

Now flip your boiler assembly back up on end.

Using a wrench, remove the steel nut from the top of the solenoid valve. The black solenoid coil should slide off freely. Next, unscrew both of the thermal switches from the top and the side of the boiler. The high temperature switch goes on top, and the low temperature (brew) thermal switch goes on the right side of the boiler.

Now remove the solenoid valve assembly from the boiler using an allen wrench. You might want to take out the rubber o-rings for cleaning if they are badly calcified.

At this point you can unscrew the hose fitting on the top of the OPV. This is most easily done when the assembly is still attached to the boiler.

Now unscrew the entire OPV assembly from the boiler. Once again, you might want to remove the rubber o-rings for cleaning if they are looking shabby.

Now is the time to remove the steam valve. This step can be a bit tricky, especially if your machine is older. I recommend removing the two bolts and twisting the valve back and forth. After some twisting, use a flathead screwdriver to carefully pry each side of the valve until it comes free. Don’t be too aggressive, as brass is a soft metal. You’ll probably want to remove the rubber gasket as well, mine was very calcified.

Next, remove the four bolts attaching your boiler to your group, and your machine should be fully disassembled! You’ll want to remove the rubber gasket from its slot in the group, if you have an older machine this gasket and its slot will definitely need some cleaning.

Cleaning

Your boiler probably looks something like the photo above and/or it might look white with calcification. Pretty nasty. If you have a lot of white calcification, a brass brush (available at most hardware stores) will take care of it. If you have a lot of oxidation and black residue like I had, a dremel tool with a stainless steel brush attachment will get the job done.

Above is my boiler after significant dremeling and brass-brushing. It’s not great, but it’s good enough for me. Although the aluminum around the seal is very pitted, I haven’t experienced any leaks whatsoever.

To clean the rest of your components, I recommend soaking them in a solution of citric acid or special-purpose espresso machine cleaning solution (available at many online retailers). This will remove significant amounts of calcification.

If your machine is as old as mine, you might need to do some more intensive cleaning. Try using a brass brush with your citric acid or espresso machine cleaner solution. Use the brush to clean off brass fittings (especially the steam valve fitting), the group, and any other metal components. This should take off any lingering calcification or other gunk.

Now that you’ve cleaned everything up, it’s time to put things back together! If you need additional help, just read this guide backwards to get a good idea of how to re-assemble machine.

The first prototype ZonCoffee v3 boards have arrived and are nearly up and running. I’m currently porting the code over to Arduino 1.0, as this board uses the Arduino Leonardo bootloader. Read on past the break for more info on the new board.

v3 Features:

• 6-Pin AUX port allows use of parallel LCD or custom expansion
• Supports SparkFun serial LCD
• USB port emulates virtual serial port for logging and loading new firmware
• All ports broken out to screw terminals
• Power via USB or external independent power source
• MAX6675-compatible footprint (also supports Maxim-IC’s newer chips)
• 6-Pin ICSP header for flashing custom bootloaders
• Main power and USB power LED indicators

This PCB includes connectors for external power, a SparkFun serial LCD, a pusbutton encoder, a thermocouple probe, a solid-state relay, and an auxiliary port. The auxiliary port pins are all connected to the ADC, allowing additional analog or digital IO for expansion. Note that the logo is silkscreened backwards, which is the only (thankfully superficial!) problem I have encountered with my board so far.

The PCB is populated with an ATMEGA32u4, an 8-bit Automotive-grade microcontroller from Atmel that features a USB interface as well as USART and SPI. This board takes advantage of USART for the SparkFun serial LCD, SPI for interfacing with the MAX6675 thermocouple interface chip, and USB for logging and updating firmware with a computer.  All parts on the PCB aside from headers are surface-mount, allowing a very compact design. For permanent installation, screw terminals can be depopulated and wires soldered directly to the board (except for the thermocouple leads, which cannot be soldered).

I have fully populated and tested two of these PCBs so far, and everything is completely functional. There are still a few software quirks from porting my original code to Arduino 1.0, but the boards themselves are fully functional. After a bit of tweaking with the encoder library and creating a drop-in library for attaching a HD44780 LCD to the auxiliary port, this design should be completely usable. I have one board up and running on my espresso machine for both use and development, and I also have a board attached to my roaster (modified Poppery I) that I will be using to experiment with ramping the setpoint for temperature-controlled coffee roasting.

Want to get one?

I’m planning on making a small beta run of boards in the coming months. Drop me an email or a comment below if you’re interested. I haven’t priced the beta boards out yet, but they will be available at a reduced price as long as you’re willing to provide a bit of feedback on the system.

Update (2/9/12)

Development on ZonCoffee has been a bit slow lately, as I’ve been working on a more time-critical project. Coincidentally, the project I’ve been working on also uses the ATMega32u4 on a much larger scale, so I can backport some fixes to the Arduino Leonardo specification to this project. I should be able to resume work on this project in the next couple of weeks.

Update (2/25/12)

I just wrapped up getting the parallel LCD code up and running, users can now switch between a parallel LCD on the auxiliary port to using a 1-wire serial LCD by changing a single define in the code. The last issue I have to deal with is my rotary encoder handling. I should be ready to do a run of the boards once I get some new encoders in to test with.

The ZonCoffee espresso PID controller board has been fabbed!

The silkscreen on the board was a bit messed up; both the names layer and my text layers were screened on the board. Nevertheless, the board appears to be very well-manufactured, and I will have a board populated for testing in the near future. The EAGLE brd file and other information will be posted as I have time.

The Eagle schematic for ZonCoffee is included after the break. Note that this schematic still has a few quirks, but it should be accurate to the best of my knowledge. I will post the Eagle project once the design is finalized.

• ZonCoffee Eagle Schematic (Full-Size) [png]
• ZonCoffee Arduino sketch & software info

Prototype using a standard Arduino

• Piezo Buzzer (optional)
• Solid-State Relay- cheap on ($6, ebay)
• Rotary Encoder with Pushbotton (~$1.50, mouser)
• MAX6675- (free sample, maxim. This is an SO package, soldering will be tough)
• Thermocouple – ($3, ebay)
• Serial LCD – ($25, sparkfun)
• Screw Shield – ($14, sparkfun). Optional, but this will make your life much easier.

Permanent project without Arduino

• Arduino Permanent Install Project ($2, mouser)
• Mega328 with bootloader ($5.50, sparkfun)
• Rotary Encoder with Pushbotton (~$1.50, mouser)
• Solid-state relay – cheap on ebay ($6)
• Thermocouple – cheap on ebay ($3)
• MAX6675 – free sample (note that it is SOIC)
• You will need an Arduino or FTDI cable to program your ATMega328
• Additional components may be needed that are not listed here, such as screw terminals for wires, perf board, etc. Be creative.

I’m looking at ways to make this project cheaper, and I think I will add support for additional display types to the ZonCoffee sketch. A cheap 4-digit LED display could be used, and would be much cheaper than the $25 sparkfun display (although more of a hassle to wire, and less flexible with data displayed).

Drop a comment if you have any questions, recommendations, or if you know any sources for cheaper parts!

Skip to Downloads

Features

• Displays set point and current temperature information on LCD
• Rotary encoder adjusts temperature targets without a computer
• Intuitive serial interface, compatible with the BBBC grapher
• Steam and extraction modes with separate temperature targets
• Simple configuration in “Options.h”

Supported Hardware (Version .2)

• 1 rotary encoder with pushbutton (software debounced)
• 1 SparkFun serial LCD
• 1 piezo buzzer (beeps when preheated)
• 1 zero-crossing solid-state relay
• 1 MAX6675 thermocouple chip (free samples available from Maxim IC)
• Additional Details

Average Hardware Cost

The entire project can be built for around $40 (not including an Arduino) assuming you acquire a free sample of the MAX6675 chip. ZonCoffee (as of .2) requires an ATMega168 or higher. The sketch is around 14kB compiled.

Plans for future versions:

• Support for additional thermocouple chips (have defines in options.h to choose which to compile)
• Support for additional display types. Possibly abstract display output functions.
• “No LCD” mode (use LED for indication).
• Release version tailored to PID for popper coffee roasting

Download

• ZonCoffee .2 [zip]
• ZonCoffee .2 [gz]

This is a build log of my PID modification to my DeLonghi EC155 espresso machine. Currently, the machine uses an Arduino to drive a solid-state relay controlling the heating coil. The Arduino displays mode and temperature on a serial lcd, and also dumps status information over the serial port.

Update 1: I’ve ordered parts for a permanent install on protoboard, after I finish the install, I’ll update this post with build instructions and details. I will also provide a link to a mouser project where you can order most of the parts in one place.

Update 3: Everything is assembled and functional, and I made an aluminum case thing for the LCD and rotary encoder. Photos to come soon. (8/25/10)

Update 4: ZonCoffee .2 is released! See the release page to download the sketch and to see additional hardware information. (1/4/11)

This post is one of a series of posts regarding mods I have done to my EC155

Required Parts:

• Thermocouple ($2, ebay)
• MAX6675 (maxim-ic) (now sold by sparkfun! 7/17/10)
• Arduino-bootloaded AVR  of some sort ($30, sparkfun)
• Solid-State Relay 25A+ ($7, ebay)
• Switch (any type will do)

Optional Parts:

• Serial LCD ($25, sparkfun)
• OSRAM SLR/SLG/SLO 2206 LED Display (driver coming to ZonCoffee soon, will require shift register)
• Screw Shield ($10, sparkfun)
• Rotary Encoder

My build is currently on a Arduino board with a screw shield, but I’m planning on making a PCB soon. I’ll update this page with links where you can purchase the PCB (probably through batchPCB) in the near future.

Software:

• Modified BBCC code (arduino sketch)
• Modified MAX6675 library
• BBCC plotter (processing sketch) [link]

Construction:

1. Installing the SSR and Thermocouple (coming soon)
2. Connecting the electronics (coming soon)
3. Editing and uploading the software (coming soon)
4. Calibrating the thermocouple (coming soon)

A few people have asked some questions about the EC155 tamper size, replacement frothing wands, etc. I’ll keep updating this page with answers to common questions.

Tamper Size

The EC155 uses a 52mm tamper (about 2 inches), and some guys over at coffeegeek have had success with the RSVP Terry’s Tamper, which weighs in at a mere $7. Note that this tamper is 50mm rather than 52mm, so it won’t fit the basket perfectly. If you’re looking for something a bit nicer, check out Coffee Compliments’ aluminum tamper ($17). They also offer all of their other tampers in the 52mm size, although they are all upwards of $17.

Frothing Wand

I’ve been looking around for a suitable replacement tip and/or wand for the EC155, and I’ve stumbled on a decent solution (thanks to people in this thread). Head over to your local hardware store or Home Depot and purchase a M6 x 1.0 acorn nut (stainless steel). Drill a 1/16″ hole in the tip, I drilled from the inside of the nut using a drill press and some 3-in-one. After drilling the hole, get a larger bit and drill from the other side  to remove burrs. Be sure to wash thoroughly before use! The tip seems to work quite well, although I think a smaller hole could improve performance.

Feel free to leave a comment if you’ve found a tip or wand that fits. For more information, check out this thread on coffeegeek.

Frothing Pitcher

I’ve found that a 12oz pitcher seems to work best size-wise with the EC155. The 12oz pitcher is also short enough to allow milk frothing with an acorn nut tip, without a steam wand extension. This pitcher (~$14)  is similar to the one I use. There are also cheaper options, but it’s nice to have a sturdy pitcher with a spout.

You can also get a cheap ($10) or more expensive ($14) frothing thermometer, or you can just use a cheap meat thermometer (which works well, although it won’t clip on your pitcher nicely).

Baskets

I’ve been unable to find much information about usable baskets for the EC155, but some people have had luck with some of the baskets listed below.

• Delonghi 606348 [amazon] – Fits, but results aren’t great (see androidmert’s comment)
• Delonghi 607706 [ereplacementparts] – Fits, but is quite large
• Krups MS-090716 [hard to find] – Fits

Portafilter/Basket Dimensions

I made the following measurements with digital calipers, so they should be fairly accurate:

• Portafilter inner diameter: 54.6mm at top, narrows to 51.2mm at bottom
• Stock double basket
  • Outer diameter: 54.0mm at widest point, narrowing to 49.0mm
  • Inner diameter: 52.8mm

Shot Glasses/Carafes

Since the EC155 has very little clearance under the portafilter, you can’t pull shots into a mug (unless you remove the drip tray, which is quite awkward). These double-walled thermo-glasses work very well, but any vessel shorter than the 2″ will work just fine.

The DeLonghi EC155 is a fairly well-built consumer pump espresso machine. It ships with a pressurized portafilter of a non-standard diameter, so finding a non-pressurized replacement is challenging. Instead of purchasing a new portafilter, depressurizing the EC-155’s portafilter is extremely easy.

This post is one of a series of posts regarding mods I have done to my EC155

Non-permanent method:

1. Unscrew the plastic retaining knob on the bottom of the pressurized filter assembly

2. Push the plastic nozzle to remove the filter assembly

3. Remove the filter and plastic piece from the gasket

4. Re-assemble the gasket and filter, leaving out the black plastic pressurizer

5. Place the gasket and filter assembly back in the filter holder

6. Note that oils and grounds can become trapped in the filter holder, so be sure to wash it often. You’re done!

Permanent Method:

1.Disassemble the portafilter down to the plastic piece with the pressurized nozzle

2. Using a pair of needle-nose pliers or a flathead screwdriver, pry off the plastic ring holding the pressurization nozzle together and remove the pin and spring.

Warning: the spring might fly out and hit you. Don’t be pointing it at your face.

3. Re-assemble and use as normal. Save the plunger, plastic ring, and spring in case you want to repressurize it later.