what stops a HX chamber from exploding (getting full of steam = bang?)

[maheel Senior Member Find all posts View Profile Close maheel]

so i was reading the below quote in the thread below.

and i was thinking about the hx chamber inside the boiler and whats (maybe) going on in it.

if its sitting inside the boiler and the boiler is +100 under pressure, what is the HX chamber doing?

if it is "boiling" why dont they go POP!!?

an old SM i had had spring loaded expansion things on the pipes but i thought they were for the boiler inlet or ??? not the HX.

anyone care to explain.

Hi Wayne,

We have repaired several Oscars over time with the same symptom and exactly as it appears on the Youtube clip. This sympton is usually the result of a failing pump, which subsequently starves the heat exchange of a suitable water vulume/flow rate and causing the overheating of the reduced water flow that does pass through it. Problems with the pressure stat tend to manifest themself with the safety valve passing with a big release of pressure. We have had one instance where even when the pump was changed, the symptom persisted and the pressure stat was the cause but generally when we have changed the pump, full water flow is returned to the group. If you are able to rig up a pressure guage and connect it to where the steam nozzle screws onto the steam arm then you can check what the pressure is but my bet is that the pump is at fault. You could also attach a small piece of tubing to the outlet side of the pump and activate the group and then watch the flow rate to see if it is reasonable before looking at replacing deciding to replace the pump as another way of checking..but you would have to know what the normal flow rate is to make the comparison.

Brad

http://coffeesnobs.com.au/YaBB.pl?num=1279077732/6#6

[Koffee_Kosmo Senior Member Find all posts View Profile Close Koffee_Kosmo]

Re: what stops a HX chamber from exploding (getting full of steam = bang?)

In Simple terms
A HX (heat exchanger) means exactly that
A series of pipes is full of water that is heated by the boiler water in an exchange or transfer of heat

The pipe strength is the determining factor as in what pressure X what temperature it can withstand

This applies to any pressure vessel

KK

[A_M Guest Find all posts View Profile Close A_M]

Re: what stops a HX chamber from exploding (getting full of steam = bang?)

Simple physics my dear grasshopper :-)


At low pressure most things boil at a lower temp... Tea on Mt Everest is boiling at alot lower that one might think and in a vacc; water will boil of at very LOW temps  

And importantly the reverse...

Guess what; if not you and I would not be here     Ya know what sort of temps etc are deep within the earth...  Massive but the pressure means there is a level of control and thus the said materials are not boiling etc...  That is until they reach the surface or a breach at a place closer to the surface..


With that in mind  re visit the statements and what was going on... Flow rates / loss of pressure management and thus the internal fluid can then boil off and cause a problem...

In this case 2 + 2 = 4

http://en.wikipedia.org/wiki/Boyles_law  

Now whats so hard about that  ;D

[Javaphile Super Moderator Find all posts View Profile Close Javaphile]

Re: what stops a HX chamber from exploding (getting full of steam = bang?)

if it is "boiling" why dont they go POP!!?  

The quick and easy answer? The HX is not a closed system. Pressure can only build in a closed system. With very few exceptions when you stop the pour a valve opens up to vent the pressure so the puck doesnt explode in your face when you remove the portafilter. That valve stays open until you hit/turn/flip the button to pull another shot. Hence the boiling water/steam has an exit point so the pressure inside of the HX system remains at ambient between shots.


Java "Hurray for Science!" phile