My long and rambling path to preinfusion/pressure profiling - Page 23

#221: Post by **AssafL** » June 9th, 2018, 3:11 pm

tonythewonderful wrote:Today I've done quite a bit of mediation and a few tests, and concluded that all my previous train of thought was in a wrong direction. First I checked what will be the flow through the jet, if I heat up the boiler to 225F, than close the mains, disable the pump, and open the brew valve. About 30 mL came out within the first 18 seconds, with the initial faster outflow which then slowed, and then it was mostly whistling and spewing - the water level dropped slightly below the jet. I thought OK, that's 80 mL/minute - the minimum flow that should be maintained so that the water level can remain constant inside the boiler.

I've been lost on this thread for the last two pages and I've got to ask:
1. You have a DB. So why raise the temp of the brew boiler to above boiling (225F)? Should be in the 190Fs or so...
2. OPV? On the brew boiler it is an expansion valve. At most it should drip. An OPV would blast and fill the kitchen with steam (love those steamy mornings - no coffee - lots of venting!).

jake_g wrote:]The LMLM actually capitalizes on this expansion for preinfusion. The brew valve opens and the pressure generated by the heated water pushes the first bit of flow through the gicleur and into the puck. Remember that the steam tables are telling you that 0.45 bar of pressure gets you a saturation temperature of 225°F.

An expansion valve on a 900ml machine (like the GS/3) drips a drop or two (maybe 5) when pressure exceeds 12 bar. It is unlikely that a smaller boiler can exude 10-20ml based on water expansion. What may be happening is that the water in the HX tube flash boils (that boiler is significantly above boiling temp) and that would push the volume of water in the tube as steam into the mini boiler and push the water out (at a max pressure of 1.5 or so bar - the steam boiler pressure).

Edit: (NB) on the GS/3 those of us who played with reduce pressure PI - we saw the same superheated HX tube water as "gargling" and other strange noises when the PI pressure was lower than the steam boiler pressure causing cavitation.

June 9th, 2018, 11:08 pm

AssafL wrote:I've been lost on this thread for the last two pages and I've got to ask:
1. You have a DB. So why raise the temp of the brew boiler to above boiling (225F)? Should be in the 190Fs or so...
2. OPV? On the brew boiler it is an expansion valve. At most it should drip. An OPV would blast and fill the kitchen with steam (love those steamy mornings - no coffee - lots of venting!).

1. Tony has an E61 DB. They utilize a thermosyphon loop just like an HX machine would. The offset temp of these machines is typically 23 to 27F. This offset is necessary to drive the TS and make up for the heat the group sheds to the atmosphere. Not a saturated group...

2. You are correct, but this is semantics. Tony is using 2 "OPVs". One after the pump to protect from spikes induced by the needle valve and regulate brew pressure (OPV), and a second one to perform the duties of the expansion valve. The second one lives between the boiler and a check valve, so the first one can't work as an expansion valve, since the check valve won't allow pressure to reach it.

AssafL wrote: An expansion valve on a 900ml machine (like the GS/3) drips a drop or two (maybe 5) when pressure exceeds 12 bar. It is unlikely that a smaller boiler can exude 10-20ml based on water expansion. What may be happening is that the water in the HX tube flash boils (that boiler is significantly above boiling temp) and that would push the volume of water in the tube as steam into the mini boiler and push the water out (at a max pressure of 1.5 or so bar - the steam boiler pressure).

YES!
I completely agree with you and recognize the misinformation posted above (by me ).

AssafL wrote: Edit: (NB) on the GS/3 those of us who played with reduce pressure PI - we saw the same superheated HX tube water as "gargling" and other strange noises when the PI pressure was lower than the steam boiler pressure causing cavitation.

I think the end-all would be to use a heat exchanger to preheat the boiler water and use the needle valve between the HX and brew boiler. In this location, the needle valve will keep the HX at pump pressure during pre-brew, eliminating the flash boiling and dribbling out of the brew group. This would likely be a huge upgrade for Chimera in terms of FLB performance and repeatable flow measurements from the group during pre-brew.

More to think about...

Cheers!

- Jake

#223: Post by **paulraphael** » June 9th, 2018, 11:21 pm

AssafL wrote:So count me as 1 person who does like it (so "no one likes the way they sound" - is now a negated hypothesis) and there may be 1 or 2 more like me.

Noted! Glad to hear someone sticking up for that thing.

June 10th, 2018, 12:37 am

ira wrote:I think the gear pump is because it's so much smaller and more appropriately sized for the job. Everyone else just uses the same pump they've always used. A standard pump outboarded would work just as well as the gear pump, just not as elegant a solution.

Ira

AssafL wrote: A "standard" vane pump is a pressure device because of the recirculation valve. The pump itself (without a recirculation valve) is actually volumetric

paulraphael wrote:The gear pump is actually set to produce a particular flow rate (on the Slayer you key in a "pump %" which I take it is a percentage of the maximum speed. The standard vane pump always spins at the same (high) speed.

Yes, yes, and yes.
The gear pump is also used in "these machines" because you have push button control of peak brew pressure, as Paul points out. Rotary vane pumps have a minimum speed to work, due to the centrifugal nature of the vanes themselves. They just can't generate high pressure at low speed because the vanes don't seal against the chamber walls. This means a bypass valve/OPV is the cost of doing business with a vane pump.

paulraphael wrote: It would be worth knowing if you're trying to do something similar to what Slayer's doing w/r/t flow control.

This is exactly what I'm trying to do. In general, I like the idea of first principles; look at a solution, and boil it down to what the problem statement really is and what the delivered solution is, aside from the means. Then ask if there is a way to arrive at a similar solution to the problem with much less effort. E.G. "This Slayer stuff is pretty cool! How does it work? Ok, needle valve, trickle flow, switch to "full power". Got it. Why the extra solenoid? Why have a gicleur and a needle valve? Wheat would happen if you left the flow restricted?" These are all questions that this topic has helped me answer.

I knew exactly what I wanted to do long before I started this topic, but it has been so rewarding having the conversation and learning the intricacies from all of you who have joined in the conversation along the way. I've been super slow to move on my project not so much out of fear, but because I am really still enjoying getting to know my machine in its new skin since just getting line pressure preinfusion. My logic here is that I won't know how to process what the end result is, nor appreciate it if I don't understand where I'm coming from. I'm also enthralled in the conversation...

A big part of this for me is understanding the physics behind it, and getting directional understanding of what I expect to happen as I move forward. The contributions of all of you have been an amazing gift to help me on my path and have challenged my understanding and really helped me get a grasp of many of the things I thought I knew. I certainly suffer from analysis paralysis, but at least my current paralysis tastes amazing!

Cheers!

- Jake

#225: Post by **AssafL** » June 10th, 2018, 1:48 am

Jake_G wrote:1. Tony has an E61 DB. They utilize a thermosyphon loop just like an HX machine would. The offset temp of these machines is typically 23 to 27F. This offset is necessary to drive the TS and make up for the heat the group sheds to the atmosphere. Not a saturated group...

I didn't think about that. Stuck in my own comfortable saturated group...

Maybe it needs a mixing valve after the boiler - a bit of cold water like the Decent??

BTW - once Tony starts using the check valves he does not need the first OPV any more.

I think the end-all would be to use a heat exchanger to preheat the boiler water and use the needle valve between the HX and brew boiler. In this location, the needle valve will keep the HX at pump pressure during pre-brew, eliminating the flash boiling and dribbling out of the brew group. This would likely be a huge upgrade for Chimera in terms of FLB performance and repeatable flow measurements from the group during pre-brew.

That is actually how Chimera's hydraulic circuit is laid out.

Filtration -> regulation -> Pump -> high resolution flow meter -> Gicar flow meter -> HX Tube -> Metering Valve or Bypass -> boiler

This was after the first few iterations gargled and sputtered; they worked - but it wasn't perfect...

June 10th, 2018, 7:56 am

AssafL wrote: Maybe it needs a mixing valve after the boiler - a bit of cold water like the Decent??

I dont think so. The offset of a dual boiler e61 doesnt need a cooling flush, so a mixing valve would just lower the brew temp. Preheating the injection water could help, but you still have a brew boiler that will flash boil when the brew valve is opened, so it's tough to manage flow control unless you're metering at the group and running the pump to keep the boiler pressure above the vapor pressure of the water @ boiler temp. I have thought of using a mixing valve on the hot TS tube on my machine to attenuate the cooling flush routine. The problem is that heat soak becomes a real concern. But it should still be quicker to purge a stagnate slug of heated water from the cold water supply of a mixing valve than it is to bring the whole TS loop into equilibrium with traditional flushing.

AssafL wrote: BTW - once Tony starts using the check valves he does not need the first OPV any more.

He does if he is metering pump output. Not to protect the vibe pump, because they aren't a volumetric device. But their output is non-linear. If you choke the output with a needle valve, the pressure spikes and the flow falls off precipitously. If you let the pump cruise at 9 bar and dump the extra flow to the reservoir, the output is much more stable and predicable.

AssafL wrote: That is actually how Chimera's hydraulic circuit is laid out.

I knew that.

I shouldn't rush replies... It was Dick that still has the HX gurgling running low pressure feed water and line-pressure preinfusion.

#227: Post by **AssafL** » June 10th, 2018, 8:42 am

Jake_G wrote:He does if he is metering pump output. Not to protect the vibe pump, because they aren't a volumetric device. But their output is non-linear. If you choke the output with a needle valve, the pressure spikes and the flow falls off precipitously. If you let the pump cruise at 9 bar and dump the extra flow to the reservoir, the output is much more stable and predicable.

So Tony has two lines from the pump. One has a check valve that is set to some mid level pressure (say 4 bar). The other has a needle valve.

If the pump is active, the pressure climbs up, check valve opens, and the main expansion valve takes over to "regulate" the 9 bar.

If the pump isn't active (PI) - the check valve is closed and the metering valve controls the flow rate.

The only reason for the other expansion valve is that if the pump is active during PI (and a solenoid activated bypass) - you would want to prevent over-pressure situations.

What am I missing?

June 10th, 2018, 9:02 am

I misunderstood this:

AssafL wrote: BTW - once Tony starts using the check valves he does not need the first OPV any more.

...to mean the check valve installed that keeps boiler expansion pressure from reaching the pump. Using the expansion valve as an OPV would work for him now that he has the check valve bypassing the metering valve with the pump engaged, but I think there is a bit of a benefit in having a cold water OPV venting to the reservoir and relegating the drip-tray bound expansion valve mounted to the boiler to light duty. Only a few drops hit the drip tray in this setup, but you are right that he could easily lower the cracking pressure on his expansion valve and safely use it for double-duty if he didn't mind the increased hot water flow to the drip tray...

June 10th, 2018, 6:06 pm

Hey guys, looks like all they fun is happening without me!

Jake, you have answered all the questions correctly, so I just wanted to clarify a couple of points, because I have been changing my machine so often that all these OPVs and others made different sense at different stages of its evolution...

By the way, my understanding of OPVs and bypasses is that they are all essentially the same - a check valve with adjustable cracking pressure. Am I right? Because I am using the same type of valve from swagelok to achieve all that functions. For simplicity I will call everything OPV, as it is too long to write "a check valve with adjustable cracking pressure"...

AssafL wrote:What am I missing?

So, stage one: vibe pump, metering valve, water reservoir.

Water reservoir -> Vibe pump -> metering valve -> check valve -> boiler 
   ^--OPV #1 (9 bar)  <---|    ball valve                           |-> OPV #2 (11 bar)-> drip

OPV #1 was adjusted in such a way is to maintain constant pressure while pump was pushing water through the metering valve. Three reasons:
1. I did not want to chock the pump with 15-16 bar - which would certainly happen [EDIT: when pump is running against MV with closed ball valve]
2. I wanted more or less constant flow no matter how open/closed the metering valve, while the ball valve was closed. The OPV would be adjusted to open at 9 bar.
3. I wanted only limited amount of water (just enough to make a shot) to enter boiler:
a. it will not cool the boiler too much [EDT: and hence will not affect the brew temperature too much]
b. not much water will be wasted by going through OPV #2, which was adjusted to ~ 11 bar to protect the boiler from over pressurisation.

Stage two: rotary pump, metering valve, water reservoir
Yes I did it! After outboardinf the vibe pump, and thinking I was going to have piece and quite, I was dissatisfied with the amount of vibrations and buzzing of all the cups during each shot.

Water reservoir -> Rotary pump -> metering valve -> check valve -> boiler 
    ^--OPV #1 (9 bar) <--|        ball valve                           |-> OPV #2 (11 bar)-> drip

Essentially the same idea, this time OPV#1 is absolutely necessary, as the rotary pump would probably just burst all the nylon piping without it.

Stage three (current): rotary pump, MV+CV, mains:

Mains (2-2.5 bar) -> Rotary pump -> metering valve -> check valve -> boiler 
   ^--OPV #1 (? bar)   <--|         OPV#3 (~3 bar)                     |-> OPV #2 (11 bar)-> drip

So, now we are all on the same page about my set up, hopefully this explains all the mysteries.

June 11th, 2018, 12:27 am

Assaf, I also have a question

AssafL wrote:Should be in the 190Fs or so...

How come? I always thought the brew temperature should be between 195F - 205F.
Also, does this mean that with a saturated group, the boiler can be run at brew temperature (or very close to it)?