Initial Set-Up of Rotary Pump Pressure

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thomgonzales

#1: Post by thomgonzales »

Please indulge me with a novice question. I have recently received my new machine, a Rocket Giotto Professional (the plumbed in version of the premium plus). I have installed a water softener and filtration system from Chris Coffee. The John Guest fittings were a breeze, once I was able to find a 3/8" to 1/2" adapter. The regulator came set at 30#.

The issue centers on brew head pressure. At 30#, the pressure never surpasses 7 bars, regardless of the fineness of the grind. By tightening the regulator pressure to say 42#, I can bring pressure up to 8 bars. Can an expert let me know if this is the proper way to adjust? I am not sure what is the appropriate water pressure should be, as the manual does not address the plumbed in Giotto. Please advise.

Various websites suggest opening up the machine and adjusting the rotary pump. I don't want to void warranties, especially on a brand new machine.

Thanks in advance for your help,

Tom.

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karl_a_hall

#2: Post by karl_a_hall »

I am no expert, but Ill share my own experience.

Changing my set point pressure does not effect my pump pressure nearly as much as a one bar swing. If my input pressure dips from 5 bar to 3 bar (which is a fun way to play around with line pressure preinfusion), my pump pressure changes only about .2 bar, if that.

That being said, it does seem that your increase of 30-42psi input makes total sense with your 7 to 8 bar increase. 12psi = 1ish bar. It seems that a rotary pump has such a high capacity that the difference between 30 and 42 psi shouldn't be increasing your pump pressure that much, if at all. The pumps are easy to adjust, not sure if that would void your warranty though, I couldn't imagine that it would since that is a part that by nature is adjustable based on the needs of the consumer.

Maybe your issue has to do with supply volume... maybe your increase in pressure actually just increased the volume delivered to the pump, which is currently being starved?!

Just my experience, there are more educated experts that will no doubt give you better advice shortly.

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karl_a_hall

#3: Post by karl_a_hall »

PS: another Chicagoian eh? Me too, far north suburbs, Highwood. I enjoy sharing espresso with other aficionados, if you ever meander my way, just PM me or e-mail me.

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shadowfax

#4: Post by shadowfax »

You need to adjust the bypass on your pump. Just tighten it a little till you get it to 9 bars. It won't take much, and this is certainly not the kind of thing that voids your warranty: it is in fact the primary method of pressure adjustment on rotary-pump espresso machines.

Edit: also, re: the observation that inlet pressure changes output pressure by only a little. Rotary pumps in espresso machines come with "balanced" bypass valves rather than the simpler "standard" ones. The balanced bypass valves have some clever trick in them that makes them a bit less sensitive to inlet pressure. The idea is if your machine is in a place with crap water pressure and little johnny flushes the toilet, your shot pressure doesn't dip as much as it otherwise would. Of course it also makes them less sensitive to upstream adjustment, hence why it's probably a better idea to use the bypass valve adjustment screw. That said, it's convenient to fine-tune your pressure with the bypass valve, provided you don't run pressure too low or too high. Manufacturers may or may not give you specs on max/min pressure for the pump you have, but if I were you I'd stay under 60 psi and run at no less than 15. YMMV.
Nicholas Lundgaard

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karl_a_hall

#5: Post by karl_a_hall »

Quick question shadowfax... my point about the low pressure causing small changes seems to be exactly what you are saying. Therefore, doesn't the fairly large swing in brew head pressure that he experiences (a nearly 1 to 1 change, inlet pressure change to pump pressure change) possibly indicate a supply volume issue? Shouldn't a 12psi change not result in a 1bar brew head pressure shift?

That being said OP, I think shadowfax and I both agree that the pump adjustment should not void your warranty at all. Paul Pratt has a good description on how to make that adjustment here... http://www.espresso-restorations.com/pumpmotor.html

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shadowfax

#6: Post by shadowfax »

Well, depending on your perspective, a ~1:1 change might be pretty good. I've never seen the numbers for how bad a standard bypass is on inlet pressure changes, but I wouldn't be surprised to find it's worse. I really don't see any reason to suspect a supply issue. Excess pressure is regulated by the pressure regulator, and if there were insufficient supply, there would be pressure drops under load that would be visible on the regulator gauge and it'd be obvious.
Nicholas Lundgaard

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karl_a_hall

#7: Post by karl_a_hall »

I am legitimately confused. Doesn't a balanced bypass valve make them "less sensitive to inlet pressure change" acc to your first post? Isn't a 1:1 ratio mean that nothing is actually being bypassed?! i.e. that it is starved and not getting enough volume to the pump to even need to use the bypass valve?

So my proposed point (hypothetical as it may be) is this... if the output pressure of the pump increased approx 1:1 (inlet pressure change:output pressure change) then the bypass is not really being used due to a lack of volume getting to the pump... thus the real problem he has is not with line pressure but line volume.

Or, does the increased line pressure somehow make the pump operate more efficiently, the line pressure increasing by 12psi (or whatever) increases the output pressure by 2-3 bar (or 1 in this case)? I just don't quite get how increasing the line pressure on a pump with a bypass by x could end up with the pump output being increased by much greater than x (let alone 2x or more) unless the bypass was not being used due to the supply/demand being approx equal. Please correct my misunderstanding.

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erics
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#8: Post by erics »

The rotary pump in the Giotto Professional appears to be fitted with a "standard" by-pass valve. Adjustment procedures are contained here: http://www.sweetmarias.com/espresso_gio ... etails.php
Most definitely your pressure regulator should be on the downstream side of your filtration/softening system and (given a lack of recommendations from Giotto) should be adjusted to AROUND 35 psi under flow conditions.

KH - your balanced bypass valve is performing EXACTLY as intended - not perrrrrfect - but darn close. :)

Pump performance curves and specs are usually presented with fixed inlet conditions or are labeled as pressure developed across the pump, i.e. discharge pressure minus inlet pressure. Short of setting up a baby laboratory, pumps having a standard bypass valve will operate at about a 1:1 ratio whereas pumps equipped with a balanced bypass valve will see negligible change in discharge pressure with varying inlet pressures.
Skål,

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

thomgonzales

#9: Post by thomgonzales »

Thank you very much for taking the time to explain. I adjusted the rotary pump and pressure is dead on now. Thanks again.

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shadowfax

#10: Post by shadowfax »

erics wrote:pumps having a standard bypass valve will operate at about a 1:1 ratio whereas pumps equipped with a balanced bypass valve will see negligible change in discharge pressure with varying inlet pressures.
I stand corrected and clarified. Thanks, Eric!

Nice find, too! That pic of the Giotto seems to show a standard bypass. That clears that up for sure....
Nicholas Lundgaard