How does Oscar's HX differ from typical e61 HX - Page 2

[cafeIKE]

If you're pumping 100+ml of cold water through the HX, that's probably close to the volume of the HX circuit, assuming 24" x ½" pipe. Temperature stability will be NIL.

Replumb the thing and put the OPV where it belongs, ahead of the HX.

[HB]

I guess there's no way to dial back the pump rate?

Other than an OPV, not really. For sake of completeness, I'll mention that some have used a Variac variable transformer to manipulate a vibe pump's input voltage and thus its effective output pressure. But that's a bit extreme.

[nixter]

I think the one thing I'd really like to change on my oscar is to have an accurate brew temp readout. As it stands I can use my PF gauge to measure brew pressure and adjust my OPV. I can use my steam wand gauge to measure boiler pressure and adjust my Pstat if needed. What I can't do is get a visual confirmation of brew temps while playing around with various flush lengths. My palate is just not that good of a gauge. I can taste when a shot is bang on but when it's a little off I'm not always sure in which direction.

So.. What am I looking at material and work-wise to get a decent temp reading at brew time?

n

[cafeIKE]

Time to take a step back.

The limitations you've covered are exactly why Oscar dropped off my list when upgrading.

Do you want to turn Oscar into a science project, expend countless hours, and probably considerably more than a few shekels, only to find out in the end that it still won't do what you want?

[nixter]

I was trying to avoid upgraditus. I only bought the damn thing in January! Ok so just cus I'm curious, what's the next step up that has pressure and temp gauges?

n

[cafeIKE]

The Quickmill Alexia with boiler PID control is probably the first off the shelf option for brew temperature stability. Note this is a single boiler, so if you steam, you wait.

e61 machines add Eric Svendson's adapter to get temperature readout.

[nixter]

Well I think the espresso gods would like me to keep the Oscar. I had been searching around for a place to buy some accurate, low psi gauges as well as a place to get a taylor thermometer for styrofoam cup tests. Turns out there's an instrument supply company that stocks both these things and it's about 4 blocks from my house.

check them out.. http://www.johnsherman.com/

Hmm.. Would any of the probes on this page http://www.johnsherman.com/therms/digisense.html be useful for a brew temp reading? I'm talking about something inline rather than styro-cup style. Couple I use that strap on pipe probe on any the the Oscar's parts to get an decent reading?

n

[cafeIKE]

A simple bead probe stuck in the thermosyphon / group junction and tie-wrapped to the pipe will give you a good idea of the group temperature. A dual input sensing top and bottom will give you an even better idea. The average less ~10°F is very close to a TC on Eric's e61 adapter. The larger question is do you want all this hanging about?

The Extech 421509 comes with two K bead probes and logging software for Windoze. About $140USD.
Omega HH-11A comes with one probe and does not log. About $65.
There are other cheap and cheerful TC meters on the net for even less. Some have got them for $10

[nixter]

This morning I picked up a Taylor pocket thermometer, a 0-30 psi gauge for the steam wand and a liquid filled 0-160 psi gauge for brew pressure. The item I'm having trouble finding believe it or not is a styrofoam cup!

n

[nixter]

Well I spent about 2.5 hours in front of Oscar armed with a styrofoam cup and a nice Taylor digital thermometer. I attempted to find a "flush and wait" cycle that would arrive at a decent brew temperature. Not only could I not find such a cycle but I could not find ANY cycle that gave predictable results! I tried brewing in 1 minute, 2 minute, 3 minute, and 5 minute cycles and none of these gave consistent temps. I also tried brewing based on the timing of the heater light to no avail either. My temps were all over the place in the range of 208.5 - 175.0 f. I know there must be a good flushing system but I'm having a hard time finding it.

One thing I wasn't sure about was how long it takes after doing some flushing/brewing for the boiler and metal to get back to it's highest temps again? 10min? 30min? If I can at least figure out how long this "reset" period is I can probably figure out how to pull at least one good shot with a simpler "flush and go" technique. I'm a little unsure of what to try next though.

[danetrainer]

I bought my Oscar around March, and I already owned the temp probe setup you see in the picture. I think that one of the things that helped me was to replicate the flowrate and volume through the portafilter when it would be properly tamped with coffee. I took a piece of aluminum foil to restrict the spout of the portafilter while I took measurements during flushes (and my measurements are inside the filter).

One thing I wasn't sure about was how long it takes after doing some flushing/brewing for the boiler and metal to get back to it's highest temps again? 10min? 30min?

I most likely need to run through my process with the temp setup again because it has been three months since I did all that testing, but to answer your immediate question here, it certainly depends on the amount of time the machine has been on. When it is in the first 1/2 hour of use it takes quite a long rebound time when the HX has been exhausted but I would say only around 8 or 10 minutes.

When its been on most of the day it rebounds really quickly, I would say 2 minutes, some things also to consider is with the pourover model and how warm the water is in the tank at the time, compared to refilling it with cold tapwater and operating it.

Just have patience and keep experimenting, you will find a satisfactory method to your flushes.

[danetrainer]

Nikolai, one question for you, do you still have hot water pouring into your drip tray during extractions? If you are, I feel you have adjusted the OPV too far and are creating too much of a loss for the volume of the HX group. When I adjusted mine, it was not ideal by any means, but I removed the valve from the machine and applied air pressure through a regulated gauge to it and turned it down to 135psi. When I pull a shot on my machine, it occasionally gives a small "squeak" as it relieves the pressure, maybe just a couple of drops.

[caeffe]

Hey Nixter, I'd be concerned you are losing hot water into the drip tray following your OPV adjustment. This could be throwing the repeatability.

Nikolai, one question for you, do you still have hot water pouring into your drip tray during extractions? If you are, I feel you have adjusted the OPV too far and are creating too much of a loss for the volume of the HX group. When I adjusted mine, it was not ideal by any means, but I removed the valve from the machine and applied air pressure through a regulated gauge to it and turned it down to 135psi. .......

I'm trying to understand so I've got the following questions-
I've adjusted my OPV also and it also dumps hot water into the drip tray. I used the portafilter pressure gauge with needle valve method (9-10 bar, x ml/ per sec etc...)
1. Why does this affect repeatability?
2. What do you mean by ".... too much of a loss for the volume of the HX group." - Why does it matter?

There's another thread here somewhere that shows how to move the OPV so that it is prior to the HX and non-heated water is dumped back into the reservoir.
Why does it matter which side of the HX that the OPV is at?

[nixter]

Yes I'm losing lots of water at the moment, probably too much that it's dropping my brew temp across the shot too much.

When I was doing flush temp testing this wasn't an issue as there was no pressure (styro cup method) and therefore no loss of hot water through the opv.

n

[cafeIKE]

Why does it matter which side of the HX that the OPV is at?

If the OPV is on the cold side of the HX, only replacement volume is injected into the HX.
If it's on the hot side, the full pump output of cold water is injected into the HX, possibly causing a bigger temperature differential over the shot depending on the temperature differential between the reservoir and the HX.

If the OPV dumps into the tray, more water is used for the shot, necessitating more frequent reservoir refills.

[danetrainer]

2. What do you mean by ".... too much of a loss for the volume of the HX group." - Why does it matter?

The HX is a small volume of brew temperature water on the Oscar, since the "bleed-off" of pressure to the group becomes a significant amount bypassing and ending up into the drip tray...causing a larger dilution of cooling water from the tank into the HX.

Think of it this way, simple terms. Your garden hose is laying out in the sun, and you want to give your dog a drink, if the hose is only 10 feet as opposed to 30 feet you can understand the time factor to get cool water out the end. Thats what you are trying to avoid in your group

[nixter]

I was just reading how there could be a large error in reading my brew pressure with the PF "blinded". First thing I will do is get a needle valve in the mix. I assume i should take a measurement while allowing about 1.5 ounces of flow in 25-30 seconds? Should I compensate somehow for the fact that's it just water and not thick espresso flowing?

[HB]

The error for deadhead versus flowing is small for some espresso machines, large for others. In a pinch I've measured brew pressure by adding a temporary gauge and pulling overextracted espresso through spent pucks. It's not pretty, but works and doesn't waste coffee.


From Testing Brew Pressure

[nixter]

Hmm.. won't a valve attached to the pf gauge assembly essentially be a 2nd opv?? How will I figure out which one to adjust and how much? Ok, maybe if I fully tighten up the opv, and then adjust the needle valve to get 1.5 ounces in 25 seconds I can then start making adjustments to the opv until my pressure lowers to 9.5bar. Hopefully my flow out the needle valve wont lessen when I make the opv adjustments.

I don't understand how using a spend puck would help with a pf gauge? Where's the over-extracted espresso going?

[HB]

I don't understand how using a spend puck would help with a pf gauge? Where's the over-extracted espresso going?

Sorry, I wasn't clear. I edited my post above to show the inline temporary gauge instead of putting a pressure gauge on the portafilter.