In an attempt to get the brew temps of my Gaggia Carezza a little more stable I experimented with filling the reservoir with hot water (not-quite boiling). It certainly helped the temperature drop off that I usually see when first starting the shot, but I'm worried if it's going to do any long term damage.

The tank itself is plastic, I'm not sure what kind, but I think it will be ok because the OPV vents there, which hasn't caused any problems yet. The hoses all seem to be the same type of rubber (silicon?) too, and they handle OPV steam. My biggest concern is the vibe pump, I assume it's using the water as cooling, any chance hot water would be too much for it?

Let me know if there's any reason I shouldn't be doing this, or anything I missed.

The Gaggia pumps are intended to pump room temp water, so your concern is valid, you may shorten the life of your pump by using hot water in the reservoir.

I have been experimenting with a "preheater" chamber, which is strapped to the boiler, and goes between the boiler and pump, so the pump is still pumping room temp water.

Randy

Ulka vibratory pumps are not rated for pumping water at temperatures above 25C. See Hot water in the reservoir? for previous discussion.

I'd considered putting in a pre-heating chamber next to the boiler, or wrapping 10' of copper pipping around the boiler, both would involve a lot of plumbing, but would probably be better long term solutions. Until I can figure out a good setup preheating some water isn't too much of a hassle for making a couple of shots, assuming it doesn't break anything.

The rating on the Ulka pumps seems conservative, I'm pretty sure the water in the reservoir gets above 25c pretty consistently, at least during the summer, or when the machine has been on for awhile. Plus, the internal temps are sure to be above that.

I'll do some comparison tasting this weekend, and see if it's worth the wear and tear on the pump.

While the pump may be rated at 25c (77F) I guarantee you the water in the reservoir gets well above that. I have measured reservoir temperatures in the 100F range on machines that run for hours at a time. Your boiler is also running around 240F and chances are your pump is within 2 inches of the boiler. I would surmise that the radiant heat form the boiler alone is well over 100F.

Long ago, when I had my Isomac, I cut the HX line and added about 5 foot of 1/8 copper tube to it. I wrapped it around the boiler as a preheat, then back into the HX input on the boiler. Then I insulated everything with ceramic blanket. I think it made a difference, but then again, the insulation could have been responsible for the change in itself. It was a lot of work, personally I would not do it again.

5 feet of .125" id tube contains 12ml, so it's flushed out long before the coffee is even wet. The water entering the tube will pick up some heat, but not enough.

Hmmm, I don't think it's worth it to try and stuff 50' of copper tubing inside that little plastic body; even if it would all fit. Given how cheap the machine is, I think some hot water in the reservoir is my best bet to get some temp stability without blowing the cost/benefit calculation all out of whack.

Taste testing to follow over the long weekend - reporting on the catastrophic failure of the vibe pump will hopefully be delayed a bit longer than that.

cafeIKE wrote:5 feet of .125" id tube contains 12ml, so it's flushed out long before the coffee is even wet. The water entering the tube will pick up some heat, but not enough.

You sure about that calculation?

Convert ft -> cm, in -> cm, plug, chug.

152.4 cm x ([0.3175 cm / 2] ^2 * π) = 12.07 cc = 12.07 mL

.125" / 2 = .0625" radius * 2.54 cm/in = 0.15875 cm radius
5' * 12" = 60" * 2.54 cm/in = 152.4 cm length
0.15875 ^ 2 * 3.14159 * 152.4 = 12.065961654
yup