La Marzocco GS3 pressure ramp takes longer - Page 2

Need help with equipment usage or want to share your latest discovery?
User avatar
Peppersass (original poster)
Posts: 3690
Joined: 15 years ago

#11: Post by Peppersass (original poster) »

erics wrote:Something is obviously amiss with your flowrates and I would look at the pump's suction line or the internal bypass valve.
When I first spoke with John, he thought the change in ramp up rate might be due to the pump bypass valve breaking in. But as I posted, when I told him my flow rate was less than 50% of normal, he suspected something wrong with the check valve in the mixing block. I'm waiting for John to get back to me on best way to remove the check valve. Evidently, it's not as easy as it looks in the photo or parts diagram.

User avatar
erics
Supporter ★
Posts: 6302
Joined: 19 years ago

#12: Post by erics »

Well, pump bypass valve "breaking in" is a little off target as that condition would then exist in one heck of lot of machines.

"Inspecting" the pump's balanced bypass valve is one heck of a lot easier than accessing & diassembling that check valve. In fact, all of about 10 minutes.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

User avatar
Peppersass (original poster)
Posts: 3690
Joined: 15 years ago

#13: Post by Peppersass (original poster) »

It appears that my problem is solved. My flow rate is up to 420ml/min, which is a tad below spec but probably acceptable and a lot better than before. Pressure ramps up exactly like it used to, within 2-4 seconds, and the first drops of espresso are appearing in less than 5 seconds. That's pretty-much how the machine behaved when I first got it.

I worked with Chris Kramer at Chris Coffee to resolve the problem. Chris didn't buy John's theory of the checkvalve on the tea water mixing block being partially open, bypassing water into the steam boiler. He pointed out that if that were the case, the steam boiler would fill with water. I added that I'd probably see a pressure rise in the steam boiler as that was happening, which wasn't the case.

Before speaking with Chris, I rechecked pressure at the group head with my home-made pressure gauge, and while it's not a Scace, it is capable of measuring the blind pressure, which agreed with the built-in brew pressure gauge: 9.5-10 BAR. I also ran some tests where I got the needle valve adjusted pretty close to 2ml/sec and the pressure read 8.5-9 BAR, very normal.

Chris's reaction was that if the pressure at the group is normal, then it's unlikely that a pump problem could be causing the low flow rate.

One quick experiment he had me do was rotate the pump to see if varying the pressure on the input and output hoses would change the flow rate. It didn't (though it did affect noise, which is another thread.)

Note: All of the following tests required powering down, unplugging and draining the group boiler through the OPV.

Next, Chris had me disassemble the flow meter, check the propeller, check the check valve, check the orifices. I found no debris and the check valve seemed OK. Then he had me remove the group solenoid valve, which is mounted behind the group. You have to remove the pressure relief tube that comes off the back of the solenoid and leads to the drain box. Then you remove a nut and washer and slide the coil box off the valve (disconnecting the electrical leads first.) Then you use a 22mm deep-well socket to remove the valve assembly. Behind it, mounted in the group, are two openings. One leads to the dispersion block and one leads to the boiler water in the group. When the solenoid is activated, the valve is pulled back, which allows water to travel from the group to the tube that feeds the dispersion block. I didn't find any obvious obstructions or debris in the valve. I stuck a 22 ga. wire down the central hole and didn't encounter any meaningful resistance. Didn't push it all the way to the dispersion block however. Unfortunately, when I put everything back together (activating the continuous brew button to fill the boiler, bleeding the group, etc.), there was no change in the flow rate: still about 300ml per minute (the flow rate improved from the 250ml/min rate I got when the problem first surfaced to 300 ml per minute after a chemical backflush during which I let the machine sit for 30 minutes.)

I might add that disassembling the flow meter is not an easy job and requires removal of two tubes that block the way. Disassembly of the solenoid valve is easy.

Then Chris had me disconnect the pump cold water output from the tea water mixing block and remove the check valve behind it for inspection. I found no debris and the check valve appeared to work OK, though I noticed the circlip that keeps the spring and valve assembly in place wasn't fully seated in the groove on one side. I snapped it in. Then Chris had me remove the group solenoid valve again and blow compressed air into the dispersion block (I have a small, portable air compressor.) I also blew compressed air into the group bleed hole. I didn't see anything come out in either instance. During reassembly, as I began to screw in the dispersion screen screw, I felt a sliver of metal at the bottom of the screw threads that was a little over 1/8" long pointing straight down. Evidently this metal had sheared off the threads as the screw was being threaded in at some point. I hadn't noticed it before. I don't think it was blocking the opening, but it might have prevented the screw from seating all the way. I can't see how that would have slowed the flow rate, though. But I guess it's possible a piece of metal might have broken off from the threads and lodged in the feed tube. I removed the sliver and deburred the opening by manually twirling a drill bit in it. When I got the machine back together, the flow rate was OK.

Unfortunately, I don't know which of the things I did solved the problem. Filling and draining the brew boiler between steps would have been too time consuming. My sense is that blowing debris out of the feed tube did the trick, but I guess we'll never know.

One incidental thing I learned during this exercise (in addition to many things about how their machine is put together and can be taken apart), is that there's no water level probe in the group boiler. I had never drained the group boiler by itself, having always drained both boilers at the same time. Well, when the group boiler is empty and you turn the machine back on, it doesn't automatically refill. It just sits there pulsing the heater (!) You have to use the continuous button to run the pump to fill the group boiler until water comes out the bleed hole. The steam boiler does have a level probe, so when both boilers are empty they both refill automatically. Sometimes the group boiler will make it to all the way full before the steam boiler fills, and sometimes you have to run the pump to finish filling the group boiler. Once I understood how it works, it made sense: the group boiler is always refilled as the pump runs, so a level probe isn't strictly necessary. This is probably the way most DBs work, but something I didn't know.

Ken Fox
Posts: 2447
Joined: 18 years ago

#14: Post by Ken Fox »

First, congrats Dick on solving the problem. One always feels a lot more confident with a machine after one has done a little surgery on it.

I am assuming that your machine is not plumbed in, by your description of your startup observations upon restarting the machine with empty boilers.

If the machine is plumbed in, with the water hooked up to the water main with positive pressure, once you open your water valve to admit water to the machine, it fills up by itself. This is assuming that you removed the 6mm screw on the top of the group in order to allow it to be "bled." I've only started my machine up from empty once, at this point. I was told to have the screw ready to tighten down once the water starts to come out of the saturated grouphead. I did this rather quickly because a fair amount of water started coming out once the brew boiler was full. I am assuming that the autofill took care of the steam boiler after I turned the machine on.

Since my initial startup 2.5 weeks ago, I have drained the steam boiler once through its valve, but as far as the brew boiler is concerned I've just run a lot of water out the tea water tap in the same cleaning session as when I drained the steam boiler.

Did you remember to remove the 6mm screw on the top of the grouphead when you refilled the machine?

ken
What, me worry?

Alfred E. Neuman, 1955

User avatar
shadowfax
Posts: 3545
Joined: 19 years ago

#15: Post by shadowfax »

Dick, of course you know I sent you this info via e-mail, but I wanted to provide it here 'for the record.' I didn't post it before, but my GS3 does 420 mL/min, the same as your now-fixed machine. According to this old FAQ thread, you are looking for a free-flow rate (a.k.a. water debit) of about 6-9 mL/sec, with right smack in the middle being 'ideal.' Technically, that's 450 mL/min, not 500 mL/min, but of course I think that's just quibbling. The point is that 420 mL/min is a great flow rate. As you'll read in that FAQ thread, lower flow rates get you a type of preinfusion that will increase the 'forgiveness factor' of your machine and make it easier to get nice shots. I believe the general wisdom is that going TOO low gets you excessive preinfusion that can make your shots taste 'muddy,' but I am not sure that's a very hard-and-fast rule. In any case, you're very near the middle of the range and in great shape.

I agree with Ken 100% on the bit about how good it is to get into the bits of your machine: taking pipes off your machine and dismantling key parts forces you to REALLY understand how it works. And it builds character.

Enjoy your espresso.
Nicholas Lundgaard

User avatar
Peppersass (original poster)
Posts: 3690
Joined: 15 years ago

#16: Post by Peppersass (original poster) »

Ken Fox wrote:First, congrats Dick on solving the problem. One always feels a lot more confident with a machine after one has done a little surgery on it.
Yes, I've realized it's not made of glass :D This thing is pretty rugged. I feel like I can probably do most repairs on it, though getting to some parts, like the checkvalve between the tea water mixing block and the steam boiler (the one John thought might be the problem) looks quite difficult.

The process has also taught me a fair amount about water flow inside the machine, supplementing the parts diagrams and flow photos on Gs3cafe.
Ken Fox wrote:Did you remember to remove the 6mm screw on the top of the grouphead when you refilled the machine?
Oh yes. Makes for a nice mini-geyser if you take the screw all the way out :) Probably a little neater if you leave the screw partway in, but then it takes a little longer to squeeze the air out.
Ken Fox wrote:Since my initial startup 2.5 weeks ago, I have drained the steam boiler once through its valve, but as far as the brew boiler is concerned I've just run a lot of water out the tea water tap in the same cleaning session as when I drained the steam boiler.
Not sure I understand that. Tea water comes from the steam boiler (optionally mixed with the cold water feed), not from the brew boiler.

Best (only good?) way to drain the brew boiler is by unscrewing the OPV above the right side of the drain box. You also need to remove the 6mm screw so air will push the water out. It'll fill the drain box. The valve is a PITA because when it's opened enough to let the water out, you can't get the drain box out to empty it until you screw the OPV back in.

I found it's best to remove the right side of the machine when opening the OPV. I believe the factory or dealer marks the fixed and movable parts of the OPV with a Sharpie at approximately the right orientation to produce a max of 12 BAR, and this is visible when the right side of the machine is removed (mine was marked, as was the one in the photo on Gs3cafe.) When closing the valve after draining, screw it all the way in, then back it out until the marks line up again. Monitor the pressure closely as the group boiler fills, adjusting the OPV so the pressure reaches but does not exceed 12 BAR.

User avatar
Peppersass (original poster)
Posts: 3690
Joined: 15 years ago

#17: Post by Peppersass (original poster) »

shadowfax wrote:I agree with Ken 100% on the bit about how good it is to get into the bits of your machine: taking pipes off your machine and dismantling key parts forces you to REALLY understand how it works. And it builds character.
I don't know what you would have thought about my character (and language) when strugging with some of the more difficult parts to remove and reinstall. :lol:

Ken Fox
Posts: 2447
Joined: 18 years ago

#18: Post by Ken Fox »

Peppersass wrote:Not sure I understand that. Tea water comes from the steam boiler (optionally mixed with the cold water feed), not from the brew boiler. (snipped)

I found it's best to remove the right side of the machine when opening the OPV. I believe the factory or dealer marks the fixed and movable parts of the OPV with a Sharpie at approximately the right orientation to produce a max of 12 BAR, and this is visible when the right side of the machine is removed (mine was marked, as was the one in the photo on Gs3cafe.) When closing the valve after draining, screw it all the way in, then back it out until the marks line up again. Monitor the pressure closely as the group boiler fills, adjusting the OPV so the pressure reaches but does not exceed 12 BAR.
Oh, that's news to me. Silly me, I thought the tea water came from the brew boiler. Since I never use the tea water for anything, it doesn't matter other than that this would make for a much easier way to periodically drain the steam boiler than going through the valve. Just continue to dump water from the steam boiler via the tea spout until you are sure that the issue of accumulating minerals is a non-issue. Then, you could drain the brew boiler via the group, although that is much less of an issue as regards accumulating minerals for obvious reasons. During those periods of time when I am home for months on end (mostly the summer months) this would be easier than using the steam boiler drain valve.

Thanks for the above instructions. I'll have reason to drain both boilers in a few days, as I am heading to France for a month next week.

ken
What, me worry?

Alfred E. Neuman, 1955

User avatar
Marshall
Posts: 3444
Joined: 19 years ago

#19: Post by Marshall »

One begins to have more sympathy for Franke's decision to sell the GS/3 for $7,500 and include on-site, local dealer service. :D
Marshall
Los Angeles

User avatar
Yeti
Posts: 116
Joined: 15 years ago

#20: Post by Yeti »

Get a Silvia... :wink: