Pressurestat vs PID for steam

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
BenS
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#1: Post by BenS »

Hi There,

Just trying to understand some basics.

When I hit the steam, the pressure immediately drops from 1.25bar to 1bar but that's not enough for the pressure stat to kick-in. Then over 10sec, the pressure drops further to .8bar which is when I hear the click. However, the element only has enough power to hold .8bar and not enough to increase it while steaming - then the milk is ready.

Because a PID is constantly on/off, would it kick-in immediately and so hold a higher pressure while steaming? Or can you get pressure stats with a narrower range so they kick-in sooner? Or is this all pointless nonsense!

Hope that makes sense.

Nunas
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#2: Post by Nunas »

BenS wrote:Hi There, Just trying to understand some basics. When I hit the steam, the pressure immediately drops from 1.25bar to 1bar but that's not enough for the pressure stat to kick-in. Then over 10sec, the pressure drops further to .8bar which is when I hear the click. However, the element only has enough power to hold .8bar and not enough to increase it while steaming - then the milk is ready. Because a PID is constantly on/off, would it kick-in immediately and so hold a higher pressure while steaming? Or can you get pressure stats with a narrower range so they kick-in sooner? Or is this all pointless nonsense! Hope that makes sense.
What you are experiencing is called dead band. P-stats always have a dead band. Often, the dead band is printed on the side of the P-stat. Even if it isn't, with the make and model, you can look up the specifications online. Sorry, I don't know what the dead band should be, but 0.8 to 1.25 sounds excessive. I do know that the Mater stats, such as the 110, are pressure adjustable, but not dead band adjustable. Also, they are not made to be repeatedly adjusted, as this lessens their lifespan. Better P-stats have both an adjustable set point and an adjustable dead band, some from CEME for example. If I'm not mistaken, the CEME can be adjusted right down to 0.1 bar dead band. I think they need to be used with an external relay, which you'd also have to add...not sure. If you need to replace your P-stat and have room in the case to fit a CEME, this would certainly solve your dead band problem. Yes, a PID for an espresso machine would also solve the problem, but at a cost and the minor bother of rewiring your machine. However, there are inexpensive generic PIDs available on eBay and Amazon, as well as solid state relays. If you have room in your machine, perhaps you could shove these right inside, to avoid having to cut any holes in the case.

Now, recovery time is a separate issue, related to the size of the boiler and the power of its heater. Even with a PID, your pressure will drop. For example, my Synchronika idles at about two bar, but this drops off fairly quickly to about 1.5 when steaming about 6 ounces of milk. On the other hand, with its reasonably large boiler (for a home machine), that 2-bar through a 4-hole tip will expand the milk to the desired level within a second or two, well before the pressure drops off much. After that, it does not matter much, as it's just a question of agitating the milk to make the bubbles finer and heating it to 60-degrees C. On larger volumes, once the machine has spent its initial 2-bar of steam, it will stabilize, I think around 1.25 bar. I keep meaning to do some tests to see how long it can keep this up, but I assume "forever", assuming the boiler does not run dry. In contrast, a plumbed-in, multi group commercial machine with big boilers, and large, often high voltage and/or 3-phase power, continue to pump out steam at a prodigious rate, nearly no matter what comes.

BenS (original poster)
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#3: Post by BenS (original poster) »

Awesome info, thank you.

Will definitely look at the pressure stat I have and see what I'm dealing with. But I also have room for one of those small PIDs we see everywhere.

With recovery, it recovers within about 5seconds (1500w into 1.5L) which seemed quite quick to me but only once the steam is off. I'm thinking that if the element kicks-in earlier, the pressure drop would be reduced?

Cheers

Nunas
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#4: Post by Nunas » replying to BenS »

Yes, having the heater come on earlier would make a difference. With one of my other machines, a small commercial HX with only 1.5 bar steam, I used to run the steam wand until the heater kicked in, then wait until just before it would switch off to start steaming. This technique provided max steam. That machine had a Sirai pressurestat; they are known to be both rugged and repairable, and they have an inbuilt relay. But, they are known to have a fairly wide dead band, thus the foregoing technique.

SutterMill

#5: Post by SutterMill »

Ben,

Thanks for asking this question. I was just considering the differences this morning as my current machine has a steam pressure stat and was pondering if it would work better with a PID. Very insightful info from everyone that chimed in.

BenS (original poster)
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#6: Post by BenS (original poster) »

See attached for shots of the pressure stat currently in the machine (it's a 969 Coffee Elba 2 IV).

Sorry for the lack of macro focus but hopefully someone might be able to figure out the current brand. Does the screw on top adjust one of the parameters? And if so, any ideas what it might adjust?

Any help much appreciated. Cheers



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Jeff
Team HB

#7: Post by Jeff »

"MA-TER" - http://www.ma-ter.it/products/pressure-switches/xp110
http://www.ma-ter.it/cache/files/XP110.pdf

One overlooked advantage of a pressurestat is it turns on 100% at the edge of the dead band. Potentially faster recovery than a PID.

Is 0.1 bar really all that much?

1.2 bar is 123.4 C, 1.3 bar is 124.9 C as I read the tables.

BenS (original poster)
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#8: Post by BenS (original poster) »

Awesome, thank you.

I couldn't figure this out based on the links, do you know if the screw adjusts the dead-band or the max pressure?

BenS (original poster)
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#9: Post by BenS (original poster) »

Sorry, re-read the first post, it will adjust the pressure-only - right?

If I wanted to replace it with a dead-band adjustable unit, which one would work best? And does being on 240v (New Zealand) make any difference?

Cheers

BenS (original poster)
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#10: Post by BenS (original poster) »

Jeff wrote:One overlooked advantage of a pressurestat is it turns on 100% at the edge of the dead band. Potentially faster recovery than a PID. Is 0.1 bar really all that much?

1.2 bar is 123.4 C, 1.3 bar is 124.9 C as I read the tables.
I see what you mean, go a touch higher? Is there much tolerance, I'm guessing yes? Would I have to replace the emergency blow-off valve (or whatever its called). Or is this all a recipe for disaster!

Curious to see how far you could push it if anyone has this knowledge?

And if I wanted to replace it with a dead-band adjustable unit, which one would work best? And does being on 240v (New Zealand) make any difference?

Cheers