The check valve is a long way from the brewhead; My worry would be that a little bit of expansion in the hose (or elsewhere along the line) would let some pressure relief draw back a little bit of coffee water come back into the line. You don't really even need reverse flow, just an open link and no flow, I would think. Ultimately the best thing is probably tuning the expansion valve and adding a leak detector. That's on my to do list...

Good point Nicholas. I didn't really contemplate the fact the hose itself could expand and absorb the pressure. I was more thinking that the pressure would more easily absorb into the boiler/OPV than into the hose itself. Either way, this was all good info to share!

Well, in case you've never seen one, here's what a pump check valve looks like.



Man, orders from Stefano via USPS get here fast as heck. He sent this on Thursday afternoon, and it's here--from Oregon to Houston--on Saturday. UPS would have charged the price of the check valve to do it this fast...

So that's all working. Other than the mount that I need to finish, I am pretty happy with the setup under the counter. By the way tom, there's only one door on the counter, and the hinges have these little levers that you can pull to disengage them, and it's like there's no door at all!

The other part of my order was a new 3 way solenoid pilot. I don't recall if I mentioned it, but outboarding the pump made me realize that the irritating buzzing I was hearing was actually the stupid solenoid valve. When I checked the coil, it was more or less fine, indicating that the pilot was having trouble opening all the way during brewing. It was rather intermittent, which also seemed to point towards some physical trouble opening the valve properly. Strange that it didn't leak in spite of the noises, but alas. The new pilot is nice and quiet during operation.

Dave's handles came in earlier this week; I don't think he understated how great they look.







They're just great in the hand, and the increased size of the handles fits my hands better. The figuring is just exquisite in person; photos can't do it justice.

Thanks, Dave!

Hi Nicholas,

I understand you removed the Pstat completely, so that now the boiler heater is only controlled via the TC+PID? At first I wanted to do the same thing, but my recent machine problems made me think again. Let's say you switch from the pstat to a TC+PID+SSR combo and it works well keeping the proper boiler pressure with minimum deadband. Now let's assume the autofill function fails badly and doesn't want to stop pumping water into the boiler. New fresh cold water entering the boiler of course means that the temperature will start falling. PID will see this and activate the heating element as it has to maintain the setpoint, so now you have pressure rising due to autofill function failure as well as the heater running at full power heating up the water building even more pressure. The same thing might happen when you have a broken boiler fill solenoid and you engage the pump when pulling a shot. Water will not flow through the coffee, but instead it will go straight into the boiler (less resistance), building up the pressure. PID will also do it's work turning the heater on and again you have the same problem.

I thought it might be a good idea to leave the pstat inside the machine and use the pressure gauge connection on the boiler to install the TC. Next you set the pstat to 2-2.5bar and connect it's relay cables to the main power supply on the machine. This means that as long as the machine is below 2-2.5bar it will have power and the boiler pressure will be controlled via the PID+TC+SSR, but if something goes wrong and the pressure rises to 2-2.5bar the pstat will switch it's relay as well as the whole machine off.

Or am I missing something obvious?

I'm still thinking of using a pressure transducer to control the pressure, but it might be a bit easier to do it with the TC (fitting straight on the boiler and I don't have to move anything around).

Regards,
dsc.

Tom, you're correct. If you can mount the pressurestat (you just need more fittings, really), it can be used as a very effective safety device. you would need to set it lower (~1.5 bars, I think), as I think the boiler safety valve will open up before 2-2.5 bar.

Another, probably significantly better safety measure is to get yourself a water-shutoff system with a water sensor under the machine, so it will shutoff the water supply and power to the machine in the event that a leak springs. This will catch a LOT more problems than a dodgy autofill or broken solenoid... e.g., small leaks, a fitting shears and starts to flood your house... that kind of thing. I'd say a leak is a much more likely problem than a dodgy autofill, too.

Let me know what you end up doing. I believe there's a thread around here about a nice safety system worth looking into... I'll probably go that route eventually. If you figure out a good way to incorporate TC and pressurestat, I'd love to know.

Hi Nicholas,

if I choose to use the TC I will probably mount it on the boiler using the pressure gauge input hole and leave the pstat as it is (with a slightly higher setting). If I have a PID which shows temperature and that relates to pressure I don't really need the boiler pressure gauge and I'm planning to get rid of the double gauge anyway (I will try to install a normal single gauge for group measurements).

Of course the pressure transducer still sounds like an interesting option, but to install it I will have to remove the pstat and try to mount the transducer in it's place. Another option would be to mount the transducer on a flex hose and attach it to the boiler using the existing pressure gauge input hole. This unfortunately calls for additional fittings as the transducer is 1/4" BSP male and the hose has a 3/8" male thread at it's end, although I might have another one with a 1/4" female tucked in a box somewhere.

Regards,
dsc.

Tom: Build something I can easily copy. I've one of the thermocouples too and was reluctant to totally trust a PID controller.

Mark

mhoy wrote:Tom: Build something I can easily copy. I've one of the thermocouples too and was reluctant to totally trust a PID controller.

Am I the only one who finds it somewhat amusing that you two have trusted those Sirai pressurestats all this time, but you won't trust a PID? If you're serious about safety mechanisms for your espresso machine, you ought to consider something along these lines...

Well the original Sirai pressurestat in mine fused shut from the looks of one of the contacts, so yes, it's certainly another point of failure...and there is a pressure relief valve so I guess it's not critical. And yes, water is much more likely to leak but worry is part of human nature.

BUT I might try writing the PID control s/w myself and I've written software for long enough to know there are and will be bugs...

Mark