bobbytoad Senior Member Joined: 11 Mar 2011 Posts: 11 Expertise: Just starting
Posted Thu Nov 24, 2011, 12:39pm Subject: Whats up with my HX machine
My Rocket machine heats up and the gauge goes up to 1.2, then there's a click, as soon as that happens the pressure gauge starts to fall and within 20-30 seconds its down to 0.9 then click goes back up to 1.2 clicks then drops off again. Similarly if the machine is at 1.2 and I open the steam valve it almost immediately drops to 0.8 within a couple of seconds and keeps decreasing. Does any one have any ideas whats going on?
Yes, it's doing exactly what it's supposed to. The pressure gauge on the machine reads the pressure inside the boiler that's built up from the head of steam that's created by the heated water. that pressur is controlled by a pressurestat (pstat). It operates as a thermostat does except instead of operating within a temperature range it regulates pressure. The hotter the water in the boiler the more steam and pressure is created. So in essence, higher pressure equates to a higher boiler water temp.
A pstat is a mechanical device. That clicking is the sound of the pstat opening and closing. Perfectly normal so don't worry bout it.
The reason it goes from .9 - 1.2 bar is that the pstat has a hi and low limit. When the boiler pressure is at the hi limit, the pstat stops the heating element. As the boiler cools, the pressure drops and will continue to drop until it reaches the low limit and will then kick on the heating element until the pressure again reaches the hi limit. It will continue to heat and cool in this range set by the pstat. The heating and cooling (pressurizing depressurizing) is called the boiler cycle. That range between the low and hi limit is called the deadband. Your deadband happens to be .9-1.2bar which is in the range of any given HX machine.
When you open the steam valve, you are releasing the head of steam the boiler has built up. So yes, the pressure drops as does the gauge reading. This will also kick on the heating element as the pstat has recognized the boiler pressure has gone below the low limit.
bobbytoad Senior Member Joined: 11 Mar 2011 Posts: 11 Expertise: Just starting
Posted Thu Nov 24, 2011, 1:57pm Subject: Re: Whats up with my HX machine
I'm new to all this but surely pressure shouldn't drop so quickly when no water or steam is being drawn? When trying to steam the pressure drops so quickly it's it's impossible to foam. I will look out to see if it startsbeat eat back up when steaming? I thought that pressure was supposed to stay even at 1.2 unless you were drawing loads of water or steam surely it shouldn't constantly go up and down when there's no draw at all?
Posted Thu Nov 24, 2011, 2:02pm Subject: Re: Whats up with my HX machine
bobbytoad Said:
I'm new to all this but surely pressure shouldn't drop so quickly when no water or steam is being drawn? When trying to steam the pressure drops so quickly it's it's impossible to foam. I will look out to see if it startsbeat eat back up when steaming? I thought that pressure was supposed to stay even at 1.2 unless you were drawing loads of water or steam surely it shouldn't constantly go up and down when there's no draw at all?
As soon as that small boilers pressure stat clicks off, there's still a tiny bit of latent heat energy being dumped in the boilers water by the heating element. After that, that small boiler begins to cool off immediately. I don't believe your boiler is insulated, but you may want to do that.
bobbytoad Senior Member Joined: 11 Mar 2011 Posts: 11 Expertise: Just starting
Posted Thu Nov 24, 2011, 2:41pm Subject: Re: Whats up with my HX machine
I'm sure the shop demo model just sat at 1.2 I can't recall it obviously and visibly going up and down in quick succession. Even when steaming the needle didn't seem to obviously move, whereas mine just plummets.
Joel_B Senior Member Joined: 9 Oct 2007 Posts: 1,823 Location: Pacific NW Expertise: I love coffee
Espresso: Astra Mega II Grinder: Mazzer SJ, Virtuoso Vac Pot: Yama 5 cup Drip: nope, french press Roaster: Behmor, WP, BBQ drum
Posted Thu Nov 24, 2011, 3:33pm Subject: Re: Whats up with my HX machine
bobbytoad Said:
I thought that pressure was supposed to stay even at 1.2 unless you were drawing loads of water or steam surely it shouldn't constantly go up and down when there's no draw at all?
yeah now that I think of it, that does sound quick. Never timed my current astra (12l boiler) but my previous astras were 2.6l and would cycle every 40-50sec. So the smaller boiler of the rocket might yield a shorter cycle time but not sure it would be 2x faster. Its possible there's a slight pressure leak or possible the water level could affect it.
bobbytoad Said:
I'm sure the shop demo model just sat at 1.2 I can't recall it obviously and visibly going up and down in quick succession. Even when steaming the needle didn't seem to obviously move, whereas mine just plummets.
as I said above water level could affect this. Out of curiosity does it change after you've opened the steam wand then close it? Does it still cycle that fast? The reason I ask is its possible to get a false pressure if you don't have a vacuum breaker.
Posted Thu Nov 24, 2011, 3:50pm Subject: Re: Whats up with my HX machine
The cycling of the boiler is completely normal. My Rocket Evoluzione cycles between .9 and 1.1 bar. It takes 14 seconds to heat up to the upper limit. It takes 90 seconds to cool off to the lower limit. The boilers parts are the same between the Rockets, so your results should be similar.
Posted Thu Nov 24, 2011, 4:30pm Subject: Re: Whats up with my HX machine
Heat up time, yes, 15 to 20 seconds would be OK. But to only take 20 seconds to lose pressure and to then turn the heating element back on... I think that there is a steam leak somewhere- the steam valve, vacuum relief valve or some other place. I can guess that if the water level in the boiler is too high it might cause faster cycling, but that is a WAG. In any case, this should be investigated.
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