HX espresso machine boiler pressure and extraction pressure

#1: Post by **Momoe** » January 13th, 2021, 3:49 pm

I think I know the answer but I wanted confirmation from you folks with more experience.

I just got a rocket appartamento and started dialing in. I got it from WLL and it seems they adjust them boiler pressure to 1 before they ship. From what I read, this is awesome that they do this because I would have done that myself once I got it. While I have never used a hx before (Gaggia classic user) before now, is it usual to see a long delay (10 seconds-ish) from start of pump to 1st drip? even without the portafilter on, it seems like a few seconds before water drips out of the group. I was wondering if for whatever reason, the boiler pressure controlled how fast the water was pumped out and built up pressure. I'm leaning towards no but wanted to make sure. I may have to find a portafilter handle to attach my pressure gauge to and see what my brew pressure is. I may have to adjust the OPV if it is too low. Unfortunately, my filter I built it on was for the gaggia and doesn't fit in the rocket's group head.

any thoughts are welcome.

I have eric's e61 group temp probe arriving saturday so I will have a real reference for temp for dialing in purposes

#2: Post by HB » January 13th, 2021, 4:00 pm

Momoe wrote:...is it usual to see a long delay (10 seconds-ish) from start of pump to 1st drip?

For a bottomless portafilter on an E61, beads will form in about 4-7 seconds. If you mean dripping from a portafilter spout, 10 seconds isn't far off, though based on taste and total time, you may want to grind coarser. See How to Adjust Dose and Grind Setting by Taste for details.

I was wondering if for whatever reason, the boiler pressure controlled how fast the water was pumped out and built up pressure.

Here's a diagram from Managing the Brew Temperature of HX Espresso Machines:

You can see that the steam pressure and brew pressure are not related at all. Of course, for a heat exchanger espresso machine, the steam boiler pressure and brew temperature are directly related. That's covered in the article above and many discussions in the forums. Here's two in particular that will help you with the "HX nomenclature" frequently used in the forums:

January 13th, 2021, 4:30 pm

I managed to attach my pressure gauge to my single spout and it looks like i'm getting about 115-118 PSI so 7.9-8.1 BAR of extraction pressure. I'm going to ask WLL if they adjusted this before shipping or what. I understand my gauge may be off but I doubt it. it's pretty simple setup. threaded pipe with a small psi gauge on it screwed into the bottom of the portafilter. I fill the filter with water and work out any air, insert to the group and engage the pump. runs up to 115-18 consistently and drops to 0 when I shut off. TBD but that may be the issue

#4: Post by HB » January 13th, 2021, 4:39 pm

That sounds about right. The pressure in the brew chamber and the reading of the onboard gauge are different because the latter is tee'd upstream of the restrictor/gicleur -- the onboard gauge will typically read 0.5 to 1.0 bar higher.

January 13th, 2021, 4:43 pm

so is 8 bar on my homemade gauge correct for 9 bar of pressure with a puck or do you agree it is a little low?

#6: Post by **Jeff** » January 13th, 2021, 4:43 pm

There's nothing magically good about "9 bar". There's reason to believe that there are benefits to lower pressures. I ran my E61 HX at around 8 bars into a blind basket with great results from medium-dark through medium-light coffees (I "never" pulled outside that range)

The E61 will "feel" slower than the Gaggia as the patented part of the E61 was an intentional, slow-start by way of a clever set of springs, valves, and chambers. This, plus the nature of a vibe pump, gives a moderately gentle start to the extraction.

January 13th, 2021, 4:46 pm

Thanks Jeff, I guess it's going to take some readjustment to this machine to get comfortable. Doesn't help my temp probe isn't installed and now my scale shot craps this morning

#8: Post by **Jeff** » January 13th, 2021, 5:04 pm

Breathe deeply and don't get over-caffeinated!

Changing machines takes time to learn not only how they work, but how they interact with your coffee, grinder, and technique. I went through about 2# on a new machine before I felt like I understood it, and another couple weeks (two shots a day, a new coffee each week) before it felt natural. What used to be a "one-mark" grind correction might now be 1/2 or 1 1/2 marks. It's just going to be different.

#9: Post by **Bluenoser** » January 13th, 2021, 8:04 pm

Momoe wrote:Thanks Jeff, I guess it's going to take some readjustment to this machine to get comfortable. Doesn't help my temp probe isn't installed and now my scale shot craps this morning

The thermometer is still a ways from the puck. It's temp won't be exactly what the puck sees. If you use a flush n wait workflow, the temp at the puck will be slightly lower. Search HB for rocket HX machines to see how they work.