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Gaggia Classic brew pressure - OPV mod? Help


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Hello everyone.

I have recently bought a glycerine filled pressure gauge and fitted it to my portafilter. I have tried many times to read the pressure while brewing and something seems quite off with the behaviour of my machine.

Right at the start it climbs quite quickly at 14 bar and then very slowly gets to around 10 bar and it settles at that measurement. Why is that happening?

I have also taken out the hose attached to the OPV valve (in the video at 02:27) and no water is actually coming out of it, so I guess it has remained untouched from the factory.

Do you suggest me to adjust the OPV to around 10 bar? So as to remove that part at the beginning where it spikes at 14 bar? Should I maybe replace the pump because it cannot sustain 14 bar of pressure? should I try and fit the pump with a dimmer to manually control the pressure? 

I'd really much appreciate your help on this, thank you in advance.

 

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Water is dripping from your gauge connections, indicating it is losing pressure. My best guess is that it takes time for pressure to build because water needs to collect at the bottom of the connector piece to seal in the pressure. When it finally does, pressure spikes to normal pressures, the OPV cuts its off at 14 bar, and then pressure drops due to imperfect seal. The 14 bar measurement indicates what the pump/OPV are set for. The 10 bar measurement is more of a measure of your device's pressure integrity. 

Using modified springs from Mr. Shades, I've been running 9 bar quite happily. Others prefer the 7 bar spring. Since your machine is adjustable with a screw, you can pick anything between, above, or below and experiment.

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Try using some PTFE tape on the portafilter threads.

Wind it on the same way as the gauge screws on (clockwise!), a couple of turns should seal it ok and give you a true pressure reading of the closed system.

The pressure in the closed system will be approximately 0.5 bar higher than with coffee in the basket so if you set the gauge at 9.5 bar it should be 9 bar when extracting coffee

Edited by ratty
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7 hours ago, SirGrindsalot said:

pressure drops due to imperfect seal.

I honestly don't think that's really the case since the leakage is minimal. I have seen many other YouTube videos where water sprays out of the connection.

Of course I have used Teflon tape on the connections, and plenty of it also. I have also used some O-Rings.

The opv does not open at all in my case, not even at 14 bar. You can clearly see that in the end of the video where I put the opv hose into a cup and not a single drop of water is let out.

54 minutes ago, ratty said:

Wind it on the same way as the gauge screws on (clockwise!), a couple of turns should seal it ok and give you a true pressure reading of the sealed system.

I will give it another try and will make the seals even tighter and more leak-proof, in order to be sure it's not from the pressure loss at the connections.

 

The question is: should I also try to set my opv at 9 bar in order not to have spikes in pressure but keep it more or less constant while brewing?

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As Ratty said ref PTFE.   Remove the wad of tape then carefully tightly wind the tape clockwise around the THREAD only 4 to 6 / 8 turns, remove any excess past the threads..

If you OPV is not moving at 14 bar I suspect it has possibly seized in position. Remove the overflow pipe and the 107 mm nut, remove the adjuster, spring and seal thoroughly clean and the bore of the valve, lubricate and replace. Set to original position and check for pressure. If it does not release now slacken off the adjuster.

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1 hour ago, El carajillo said:

If you OPV is not moving at 14 bar I suspect it has possibly seized in position. Remove the overflow pipe and the 107 mm nut, remove the adjuster, spring and seal thoroughly clean and the bore of the valve, lubricate and replace. Set to original position and check for pressure. If it does not release now slacken off the adjuster.

Thank you. I will do that and will update this post, I am either way planning to tear every piece apart and clean it thoroughly, I am guessing there is quite a bit of scale buildup inside although I can't notice any sign of clogging. Do you know the Durgol Swiss Espresso descaler? I've got 2x 125ml bottles and I'm asking myself if it's enough. 

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