2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

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haroldo_psf

2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

It comes down to this question. I don't believe this can be done with our vibe pumps. Please do an experiment and let me know.

In my case, the minimum I can pull 2oz in the correct pressure range is 40s. How about you?
Last edited by haroldo_psf on Thu Mar 19, 2015 2:15 pm, edited 1 time in total.
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chas
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Re: 2oz in 30 seconds or less at 9 bar. Minis and Dream Ts: can you do it?

Post by chas »

Adjust the pump pressure up so you can grind coarser.
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

The group pressure gauge taps into the plumbing near the output of the pump. The only time the gauge will give you the same reading as you see at the PF is when you have a blind basket installed. As soon as you have coffee in the PF and water is flowing, the pressure at the puck can be quite a bit lower than the pressure seen on the gauge. So if you are seeing a pressure lower than 9 bar while pulling a shot the pressure on top of the puck is even lower.

On my machine, in order to get 9 bar at the puck when pulling a ~30s shot of 2 oz, I need to set the pressure so that the gauge actually reads 10.5 bar.
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Post by haroldo_psf »

Thanks chas. The pressure adjustment on my machine, from what I understand, is not a pump adjustment, but merely an adjustment of the pressure relief valve, so that wouldn't help.
I'm considering returning the machine :(
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

The pressure adjustment on tank models uses the same part as the expansion valve used on the plumbed models. However, on the tank versions it attaches via tubing to the output and input of the vibe pump. The valve is adjusted to open at whatever pressure you want to use. When it opens it shunts water from the output to the input of the pump. As soon as the pressure falls it closes. Rinse and repeat. This is why the pressure needle vibrates on the tank models. It is vibrating at the rate that valve is opening and closing. IMHO, they should have used a dampening gauge to get rid of those oscillations.

Most vibe machines either do it this way or else they shunt the water from the adjustable valve back to the tank rather than to the input of the pump.

Even though the adjuster is built into a rotary pump, the basic control mechanism is the same, just a more complex design.
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haroldo_psf

Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

Chas,

Still, adjusting this valve would limit my maximum pressure, correct? I already know my max pressure is set at around 9.5 to 10 bar from testing with a blind filter.

With this adjustment in place, if I can't get 8-9 bars in a certain reasonable flow rate (2oz/25s), there is nothing more this adjustment can do for me, is there?
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

You have plenty of leeway, just tighten up the adjustment nut until you get the pressure you are looking for at the puck. Set it to 10.5 bar with the blind basket in place and see how that works.
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haroldo_psf

Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

I'll try this in a bit, Chas. But theoretically, I don't see how that could help. If I already read a higher pressure on the blind, and if I can't achieve that pressure at flow, increasing the OVP setting won't change the pump output capacity, just raise the pressure release limit, right?
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

The pressure adjustment works by shunting water from the pump's output back to the input. You increase the pressure and the water flow by shunting less water back to the input. Therefore you get more pressure and more flow at the group.
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

But Chas, doesn't shunting occur only if the line pressure overcomes the pressure threshold of the OPV, which now is 9.5?
I just tried really hard now to pull 2oz in 30 seconds. I went all the way down to 14g in a double basket (kept grind the same as my 18g normal dose in the triple).
My normal 18g 2oz pull lasts 40s at 8 - 9 bar. At 14g, the pull took 30 seconds, and the pressure was in the 6ish bar. In this scenario, assuming the answer to the question above is yes (shunting only if line pressure > OPV threshold, which now is 9.5), I don't see how it would help...

Now, if the shunting is not discrete, but continuous and (non) linear, then I can see how it could help. What do ya think?
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by jfrescki »

Something doesn't seem quite right. For instance the video of the shot I posted yielded 24g from a 15.5g does in 28 32 seconds. If I let it run, I would have had 31g, a technical normale, in about 35 seconds. Most of the shot was about 8.5-9 bar, and never went below 8 bar. I'm not sure why you need to grind so tight that you need 40 seconds to keep the pressure up.

I believe all shots run faster as they progress, even with a rotary, and as you pointed out in a post, the rotary machines read pump pressure, or they wouldn't show 9 bar with no portafilter. So even though a rotary may read 9 bar, I can't believe 9 bar is making it's way through the puck the whole time, right? Or am I way off base. Maybe Chas can chime in.

EDIT: Don't get caught up with 2oz either, that's likely to be way off base. The accepted way to quantify your shot is weight of dose vs. weight of output. 15g does yielding 30g in the cup is your starting point, adjust to taste.
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Post by haroldo_psf »

Guys, thanks a lot for the input. I figured for a $400 difference, it's not worth the headache of being in doubt. So I just placed an order for the Dream plumbed rotary version, and set up an rma for the Dream T. In a week when it gets here, I'll unbox one, box the other, and carry on :)
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

If you live in a situation where you can plumb in an espresso machine, then the Dream is the machine you should have started with. Once you've plumbed in you'll never go back. I'm not sure I agree with the specific rationale behind your decision, but you won't regret it.

Are you also going to order the Chris Coffee Filter system with John Guest connectors plus water pressure adjuster/gauge? Unless your water line pressure is 45psi (3 bar or less) already, you'll want to reduce it to 3 bar to get the most out of the preinfusion should you opt to use it.
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haroldo_psf

2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

Hi Chas
I can plumb the machine, but I decided to run it off 5 gallon bottles (one for supply, one for drain), plus a flojet and accumulator tank. No need for filter that way. I'm also out off my wife's kitchen that way with a whole cafe bar room just for myself
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Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by chas »

The way the Flojet works is that it senses the suction from rotary pump coming on and immediately powers up the flojet pump. Therefore, preinfusion may NOT work since the pump is not on during preinfusion. Of course, if there is enough residual pressure in the accumulator during preinfusion, you may be OK.
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haroldo_psf

Re: 2oz in 30 seconds or less at 8-9 bar. Minis and Dream Ts: can you do it?

Post by haroldo_psf »

chas wrote:The way the Flojet works is that it senses the suction from rotary pump coming on and immediately powers up the flojet pump. Therefore, preinfusion may NOT work since the pump is not on during preinfusion. Of course, if there is enough residual pressure in the accumulator during preinfusion, you may be OK.
hmm. I thought the way the accumulator (pressurized to 20psi from factory) and flojet combo worked was in the range of 20 to ~45psi (cut off pressure of the flojet).

I don't know the minimum threshold of the flojet, I thought it was in the viscinity of the 20ish psi? Meaning, does it actually have to sense negative pressure to activate? I thought it sensed a pressure lower than a positive threshold, about 20psi give or take.
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