Sainsburys Espresso Machine Explosion: Industry effect?

If you haven’t heard this story yet click here first (new window).

Thankfully there were no fatalities or serious injuries sustained. Bloody lucky really judging by the mess of the boiler….. If you’re not sure how an espresso machine boiler works I’ll briefly explain. The boiler is1/2 to  3/4 full of water. This water is then heated with an element. Unlike many other “heating” systems an espresso machines element is controlled by a pressure switch not a thermostat. That is to say that the element heats the water until the water heats and generates steam. The steam is trapped inside the boiler and the water keeps being heated and the pressure raised and becomes a pressure vessel. The water will be over 130 degrees C in a pressurised state. (Just like your grandmothers pressure cooker!)  When the  machine reaches a certain pressure. (just above 1b) the element cuts out.  Once the pressure drops (I.e. the release of pressure via a steam wand, or the introduction of cold water from the auto fill system) the element is switched back in to bring the pressure back up.  What happens then if the pressure switch fails? Well either it will stop the element switching in or LEAVE it switched IN. In this case the element will heat the water and the pressure will continue to build until something gives. If the machine has been maintained then the safety pressure valve should operate and release the pressure. If not it will be the next weakest thing point. Probably a leaky gasket. The pressure will just make the hole bigger and it will go bang!

The one question that has echoed around the coffee forums and Twitter today is this: ” Why didn’t the pressure release valve operate?”

Good question! The reason for having your espresso machine serviced every year isn’t to make your espresso taste lovely or so your friendly neighbourhood coffee company can rip you off. It’s to keep the thing safe and in good working condition.  It checks pretty much every working part,  replaces any that are faulty and highlights any potentially faults. It renews all the important seals (of which there are many)and de scales the machine where appropriate. Safety mechanisms are tested; primarily the pressure safety/over pressure valve.   Not only will this ensure the machine is safe but it keeps the most important tool of your business running smoothly! The last thing you want is an important part like the pump/pumphead (a good example of failing part an engineer can spot really early on) to fail at 8am on a Saturday! Not only would it mean business downtime it will cost double to get an engineer out over the weekend/if at all!

Unfortunately it’s all to common for operators not to bother and avoid the cost.  They just keep on going until something lets them down.  Not only does this cost more in the long run but they are really putting themselves at risk!  In my time as an espresso machine engineer I’ve lost count of the times I’ve found a machine an a total state due to lack of regular servicing and on several occasions I’ve come up against a stuck fast pressure safety valve. It’s only a tensioned spring and a plastic seal and needs to be maintained.

Certified Pressure Safety Valve - My valve of choice!

If you are an owner of a coffee business then you may have heard of a Pressure Vessel certificate. To my knowledge (so I’m probably wrong here) it’s not illegal to operate a machine [within a business premises] without one. (although your insurance company may need one to issue cover***) However, it is law that your pressure vessel/namely your espresso machine receive a regular/yearly service and should be policed by your local EHO.  It’s a subject that as a machine engineer I have done much research into.  HSE guidelines are pretty vague at present. It’s pretty confusing as to who can actually issue a certificate in the first place. The guidelines say “A competent person” but then fails to elaborate on what passes for competent!$$$

You can bet that after this latest incident that local authorities will get pretty damn twitchy and the guidelines will have to be made clearer. I’m hoping that it will also make operators think about their own machines. For some reason operators see a service with suspicion. I’ve had it put to me that the service is there just to make money. Several customers have had a first service for years because the EHO happened to ask about their service record. One customer said that he avoids them because the last one he a repair it caused loads of problems a week later.  Well, yes possibly. If you haven’t had a service in years then there is of course any work might cause another problem. One good example is the pump head. A failing one will show up way before is dies completely, but will struggle on for an age & slowly get worse and the pressure getting lower. On a low use machine, a restaurant say, then it could even last a year or two. When your friendly engineer replaces this (usually because he wont pay for a service, just wants the problem fixed) all of a sudden you have the machine pumping 9bar and putting loads of stress on other parts. This is when old seals/gaskets start to fail. If this machine had recived a yearly service then the pump head fault would have been identified and replace WAY before it got too bad.

PLEASE PLEASE PLEASE  get your machine serviced every year, possibly even more under really heavy use.  You can bet your life that the EHO will come knocking very soon asking about your service record!

$$$ If you have any more info on this please feel free to comment and correct me and I’ll edit the post.  Are you a distributor, engineer or operator? Get in touch below and share your thoughts. What impact has this had on your business?

***One of my customers had this problem. The insurance company insisted that an HSE inspector (an EX naval steam engineer) inspect the boiler. Unfortunately for my customer the inspector insisted that the boiler be removed and stripped prior to inspection. This meant that I had to remove the machine to my workshop then MY WORK I WAS TO BE INSPECTED to ensure that I put it back together properly and installed the pressure safety valve correctly! That was a fun day!!!!


~ by Lee Wardle on September 14, 2010.

9 Responses to “Sainsburys Espresso Machine Explosion: Industry effect?”

  1. A well written. informative and thought provoking article Lee.
    This should be a wake up call for the industry. It’s the same as having a smoke alarm but never checking the batteries…

  2. A good article and as a Coffee Machine Distriutor we feel that this will ultimately help the industry.
    We are under the impression “A Competent Person” is a person who has had the authority and training and is certified to produce a “Written Sceme OF Examination”. The actual boiler inspection is a relatively simple excercise and we understand the process to be as follows:
    The boiler is to be emptied and the element removed. The Boiler is then examined internally for any defects. The safety valve is then tested to 2.8bar. If the valve fails then a new valve is installed. The machine is then put back to working order. 45 minute process.
    The inspector is usually from the insurance company and the manual work is carried out by a authorised Espresso Machine Engineer.
    We already offer this service but customers are reluctant to pay for this!!!

  3. Hi, I don’t think it is wise to speculate as to who may be “competent” and what may or may not need testing when dealing with peoples lives. It is also extremely worrying to see figures like 2.8 bar being quoted for the safety valve release pressure as this is very wrong and actually dangerous advice should it ever be attempted.
    Why speculate? Why risk a repeat of Sainsbury’s?
    Use an espresso machine manufacturers service department as they HAVE to fully understand and adhere to the regulations by law.

    • I’m pretty sure that 2.8bar is the blow of calibration for a safety pressure valve. David runs a company that employs espresso machine engineers and I am one. The speculation wasn’t about who is competent to service/test/work on the machine, it was about how English Law defines someone legally qualified to issue a pressure vessel certificate to satisfy the HSE.


  4. Vincent you are missing the point of these comments and my comments. We want the industry and the users to be more aware of the dangers Pressure Vessels pose. This is not the responsability of the manufacturer but of the user of the machine. What we want this issue/problem brought into the public domain so users of pressure systems understand there legal resposability and are legally forced to conduct these Pressure System tests anually. At the moment these test are not being done because users/owners will not spend the money and NO ONE is enforcing this legal requirement on a regular basis. It is up to the Health and Safety officers to enforce this legal requiremnt when inspecting individual premises. If a espresso machine does not have a valid certificate then they should ensure the machine is shut down until they do. Lastlty Safety valves should blow at either 1.8b or 2.8b depending on type of pressure vessel and seafety valve installed. CE marked safety valves are set at 1.8 bar.

  5. I own an Espresso service company and wish to advise the correct pressure for a safety valve blow off is 1.8 Bar, most espresso machines have a mark on the pressure gauge at 1.8 Bar for this reason.(The safety valve will also have a stamp on it) I currently carry out the inspections with an inspector from the sites insurance company. It is very important that the test is carried out and even more important that it is completed correctly.

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  8. Hi, I am interested in training to be a coffee machine boiler pressure tester. I can’t seem to find any courses on the internet and wondered if you have any details?

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