Should I PID my Heat Exchanger? - Page 2

Want to talk espresso but not sure which forum? If so, this is the right one.

#11: Post by expressotaglong »

I'll second erics take on Swagelok stuff. Their small diameter tube fittings are good for gripping stainless sheathed thermocouples. Another good source for BSPP fittings and adapters is Parker Hannifin. The Tube Fittings Division catalog is a good place to start looking for European fittings and adapters. This catalog has a wealth of information on almost any threaded pipe fitting you will find in an espresso maker.

BSPP is very common on European industrial equipment. The threads and how the fitting seals is unlike anything else in common usage here in North America; you will not find them in any hardware store. In my experience European equipment can feature a mishmash of fitting types. I once worked on Swiss die casting machine which, in addition to the usual metric threaded stuff, featured 2 varieties of British pipe threads, two different SAE fittings, and one oddball (non-ISO) DIN fitting. If you are doing some machine plumbing modifications you may want to look at the Port Details section in the aforementioned Parker catalog. Case in point, the tapered pipe fittings you see in your machine are probably BSPT, not NPT. I've seen people cram the two together but I'd avoid doing so with high temperature pressurized water. The good news is that as Parker swallows up manufacturers worldwide they have become a one stop shop for European spec fittings and valves.

Whether you get your fittings from Swagelock, Parker, or whomever, be prepared to pay an inordinate amount compared to your local hardware store. These are high quality industrial fittings, the same ones your machine was built with, and their cost is part of the reason why good espresso machines cost as much as they do.


#12: Post by jasonmolinari »

I'm trying to follow what is going on here, thinking about putting a PID on my Isomac Tea.

Ken, clarify a few items for me.

1) If you have the boiler temp at 236 or 241, wouldn't the water in the heat exchanger be overheated, just like it would with the pressure stat? If so, i assume flushing is still necessary.

2) Would it work to set the PID temp the the desired brew temp, and purposely let the heat exchanger water (the 3 or 4 or 5 ounces) equilibrate to this temperature? Giving you optimal set point temp for the first 3-5 ounces, and then requiring the machine to sit idle to let the next "charge" of water in the HX equilibrate?

Doing this obviously would eliminate the steaming potential, making the HX machine one big ole single boiler machine, but PID controlled. Optionally, a 2nd set point on the PID could be set above this, to allow steaming.

Is what i'm asking clear?


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#13: Post by eastpresso »

Hi Ken,

would you mind to share where you installed the probe on your pourover machine? There are no unused ports on the old Junior so the most likely location (without any modification) would be the drain plug?

Thanks in advance!

Ken Fox (original poster)

#14: Post by Ken Fox (original poster) »

I removed the pstat and in its place, through the port that it used, is where the TC resides in my pourover machine:

You do "lose" a bit of redundancy by doing this, and theoretically you could get the rare occurrence of the SSR breaking and freezing in the "on" position, in which case you risk having your boiler safety valve blow.

Other than drilling an extra hole in the boiler, or (possibly) figuring out how to "T" in the probe through the port used by the pstat, I can think of no other easy access point for a probe in this machine.

What, me worry?

Alfred E. Neuman, 1955

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#15: Post by eastpresso »

Thanks a lot for the picture and the explanation.

The pstat port is fairly high up - looking at the picture (and the tubing) it seems indeed boiler pressure is measured by hot water pressure and not steam? The difference in boiler level (due to manual fill) is close to 3cm. It is difficult to tell whether the lowest position of the pstat port corresponds to the min level on the sight glass, although I would assume that this would be the case? Did you bend the probe in addition? What length did you use?

Any thoughts on using the drain plug (other than that is a lousy position to get to and that it's used for a different purpose too)?

Ken Fox (original poster)

#16: Post by Ken Fox (original poster) »

You are right that the Pstat port is high and that a TC probe put there (unless bent) will be in the steam column rather than the hot water unless you have overfilled your boiler. This is of no concern as the steam temperature is in equilibrium with the water temperature; it can be no other way. I doubt there are any response time issues of consequence. My probe goes in straight. The probe in my rotary machine is also in the steam column, by the way.

I don't remember the exact length of my probe; what I would do in your situation would be to stick a long straight wooden stick (such as those used to skewer food for barbecuing on the grill) to measure the amount of room before you run into something, with that "something" undoubtedly being the heat exchanger, then make it a little less long than that. I believe my probe in that machine is about 3" long but that is from memory a long time ago and I'm way less than certain on that.

As to the idea of using the boiler drain port for a TC Probe, I can't think of very many worse locations. A PID is not necessary for the operation of your espresso machine, but the ability to drain the boiler MIGHT be, should you need to change the element or get into the boiler for any other reason. You will probably be unable to put anything other than an extremely short probe in there for mechanical reasons, which may give you readings little better than a surface probe taped to the boiler. In addition the probe will probably bang into the element on the way in, and would interfere with removing the element should it fail or its removal be necessary for some other reason. I would not under any circumstances consider the boiler plug as a location for the probe if it were my machine.

What, me worry?

Alfred E. Neuman, 1955

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#17: Post by cafeIKE »

A 0.125" probe has a time constant of about 10 seconds in air, 0.33 seconds in water.
A 0.0625" probe has a time constant of about 4 seconds in air, 0.23 seconds in water.

As HX boiler PID tuning functions over a very wide range, and the boiler thermal inertia is measured in minutes, location in the steam area will work fine. Ken is spot on asserting that existing functionality should be maintained.