Has anyone tried taking the pressure measurement from the steam wand? You may only need a VERY STRONG hose, two hose clamps and a pressure gauge. The advantage is that you could see the pressure while brewing.
i used a car tire pressure guage, some hose clamps.
and for the hose..... du du dah dahhhh.. i used some fuel line hose that was padding my knock box. :D
later on i went to auto zone and got a "scrap piece" of fuel line for free..
put the guage on one end and clamp. take off your steam tip and clamp hte other end of the fuel line to the steam wand. open the steam wand all the way and watch the pressure cycle with the heater element.
I followed your instructions and now I have an inexpensive portafilter mounted pressure gauge also. I have a problem though: 1) the dial face of the pressure gauge fills with water when the machine is in brew mode .....is this normal? Or do I have a defective gauge?
2) the reading I'm getting on my stock Gaggia Color is approx. 130 psi or 9 bar ( which is the pressure I was hoping to set my machine to after adjusting the opv. ) Is it at all possible that this machine was already adjusted to 9 bar when it shipped from Wholelattelove three months ago? I expected that it would be closer to 14. Perhaps the gauge is defective and is coincidentally giving me a readibng that is perfect for well brewed espresso.
Depending on the gauge you have, it's pretty normal for the dial to fill up with water (though it is annoying).
Is any liquid flowing when you are measuring 9 bars? I don't own a "Color" model but I believe that is one without a 3-way solenoid valve. So if your PF gauge is watertight (nothing dripping from the Portafilter at all when you are measuring pressure) I would expect the pressure reading to drop substantially when flowing the equivalent of a double shot.
Ideally you would be able to flow 1oz of liquid in 25 seconds to simulate a ristretto or single shot and still read 9-9.5 bars while that amount of liquid is flowing from the PF. And to simulate a double (depending on what you generally like to pull as a double) you should be able to flow 1.5oz to 2.5oz while the gauge continues to read 9-9.5bars.
This is controversial (many people don't believe my results) but I found in my testing that machines without a 3-way valve have a varying pressure in the PF depending on how much they flow during the shot (because of the tension of the spring loaded valve in the group). I found that depending on how strong/weak that spring is you may get 9 bars when flowing 1oz in 25 seconds but only get 6-7 bars when flowing 2oz in 25 seconds. I found that I could stretch (or compress) the spring a little and tune the valve to get the 9 bars for my preferred shot volume and it works pretty well.
I didn't have a needle valve to adjust for precise volumes of flow when testing ... but I found I could simply loosen the fittings a little so a little water dribbles when testing. I captured all that water in a bowl underneath the Portafilter and weighed it. It was fairly easy to simulate a 1oz and a 2.5oz shot in 25 seconds and see the effect on the pressure gauge.
I manage to get very good shots on Gaggia machines without the 3-way valve ... but I really prefer the Gaggia with the 3-way valve because the pressure is more consistent regardless of shot volume so I can switch between a ristretto and a normale or lungo and know I will get the same brew pressure ... without the 3-way, I stick to the shot volume that the machine is able to hold 9 bars (and testing 3-4 different identical model Gaggias shows each of them different)
No there is no liquid flowing when I check the pressure. I'm using a store bought gauge that I attached to the portafilter creating a closed pressure system. I had expected to 'pin' the gauge all the way! But It barely got to 120 psi which I believe corresponds to approx. 8.5 bar. There was some leakage of water around the gasket above the portafilter which leads me to believe the pressure must be much higher than what I've seen reding on the gauge because it's never leaked there. Only when closing the entire system for a reading like this. It's a new machine which functions normally in every respect.
I'm having trouble getting my pressure gauge to work. I built one according to the parts list you gave and it's reading 8-9 Bar and leaking a bit from the Group Gasket even though it's a new machine and the portafilter turned in very tight. I'm proceeding now simply tightening the pressure gauge parts and going a little tighter (if that's possible) on the portafilter engagement. Any thoughts?
Did you remove the basket? If not, it leaks between the basket and PF. Normally the pressure is in the puck in the basket with the bottom open. With the bottom occluded water comes back up and over the lip. I did not read the whole thread, sorry if this was already covered.
Ah hah! That is quite a satisfactory and useful answer. I will check that out. Yes I did have the basket in when I took the reading.I will now remove it before attempting another reading. I'm also in possession of a bit of news from another CG member which states something to the effect of a group valve spring which must open for water to flow from the boiler to the group thereby reducing the effective pressure emanating from the pump by quite a substantial amount! ( Oh the things one can learn about an espresso machine!)
Yeah ... once you take the basket out, the handle will swing further before it tightens up but it should then seal against the gasket and I expect you'll see closer to 11-12 bars when there are no drips at all.
Once you get to that point, try loosening the fittings a little until you are leaking about 1oz - 2.5oz in 25 seconds (or whatever volume you consider to be your desired shot volume) ... notice what pressure you are reading then and let us know your results.
I happen to like my doubles to be ristretto - I find that pulling 1oz shot from 17-18 grams of coffee is about perfect to my taste. I'm able to get very good shots of that volume from the cheaper Gaggia machines ... but I find the pressure to be lower than 9 bars when trying to pull the more common 2oz in 25 seconds.
But they are all a little different (based on how strong the pump is and how strong the spring is in your group valve) ... so it'll be interesting to see what yours delivers since I've never tested those newer models.
I too am interested in what someone else sees for pressures. I don't think I'm having any issues just always curious.
I put about 16g in my basket, with a bottomless PF. About the time I see blonding I cut the shot off, and yield roughly 2oz in roughly 25sec (slight variations depending on my tamp and as the beans age, but around that). I see right around 130 - 135psi during these shots, and just over 140 when I use the blank basket to backflush. So maybe 8psi-ish (1/2 bar-ish) loss for me when making a shot vs. the system sealed up. This is with a glycerin filled gauge attached full time between the pump and boiler, by the way.
When I was setting my OPV I cracked open the steam wand just a tiny bit so that I got about 2oz over 25 seconds out of it, and had the blank basket in to seal things up there. I figured that approximated flow through a coffee puck and set my OPV that way. It was a lot of fiddling - taking the cap off, adjusting it, putting it back together, trying again... but after 3-4 tries I got it close enough. Seems to have worked.
You have a 3-way valve in your machine though, right?
Pittsbri's machine doesn't have a 3-way valve ... instead his has a spring loaded valve that resists 3-4 bars of pressure. These behave very differently and the pressure change can vary a lot based on the shot volume. These type machines usually don't have an OPV (and IMO don't need one). They also interact much more with the resistance of the coffee puck than the OPV does (with a 3-way, the OPV is in parallel with the resistance of the coffee puck while the spring loaded group valve is in series with the coffee puck).
Going from a 1oz shot to a 2oz shot might result in 2 bars difference with a group valve where it might only result in 1/8 bar difference with a 3-way valve/OPV type machine. And going from blind filter to flowing 2 oz might be 5-6 bars difference vs the 1/2 bar difference you see ... so they are really two very different animals in this regard.
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