La Marzocco Brew Pressure Issue

December 27th, 2012, 8:12 am

Hello, I'm new to the forum...would appreciate some advice. I have a La Marzocco Linea 2 group. My question is about the dispensing pressure. Is it suppose to stay steady? When not in use it can be anywhere from 3 bars to 12 or so bars. When it dispenses it only goes to about 7 or 8 bars. My shots are only at about 120 degrees once pulled. So all that being said.... Is it ok to adjust the valve so that get a 9 bar pull and not worry about where it is when not in use? I don't want to blow anything up!! I hate dealing with pressurize things!

Thank you so much for your time!
Cindy

#2: Post by HB » December 27th, 2012, 9:13 am

The brew pressure gauge reading should be steady when pulling a shot at around 9 bar. When idle, the brew pressure gauge shows the pressure of a closed system. I elaborated on this point in another post:

HB wrote:The pressure reading when the machine is idle isn't important.

To elaborate, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the boiler warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water into the driptray to avoid subjecting the hydraulic system to excessive pressure. It only needs to let a few drops of water escape to reduce the pressure sufficiently.

So, as you assumed, there's no need to worry about the gauge reading when the machine is idle as long as the reading is < 12 bar. For your reference, below is a reminder on how to adjust the brew pressure.

HB wrote:You should find a pressure adjusting screw similar to the one shown below:

From Procon exploded view; also see Adjusting espresso machine's rotary pump brew pressure?

Counter-clockwise = more water passes from outlet to inlet through the bypass valve = lower pressure. Clockwise = less water passes from outlet to inlet = higher pressure. The adjustment is fairly sensitive, i.e., one-half turn should produce an immediate increase in pressure. If not, the relief valve could be stuck; it's also possible there's an obstruction along the way to the brewhead (e.g., the gicleur could be clogged with scale). To confirm or eliminate the pump as the cause of the problem, tee in a pressure gauge immediate after the pump. It will show the pump's output directly.

#3: Post by **shawndo** » December 27th, 2012, 12:12 pm

Some other discussion on adjusting the pump:

La Marzocco Espresso-only Shot Brewer

erics wrote:This is how you do it . . . with the water supply to the machine SHUT OFF, slightly loosen lock nut (2), turn adjustment screw (1) about 1/4 turn counterclockwise and retighten lock nut only finger tight. Open water supply and brew into a blind basket, adjusting pressure to your desired value.

Now hold adjustment screw stationary and gently snug up locknut past fingertight - maybe 1/12 of a turn. Recheck pressures with the machine fully warmed up and while brewing a typical shot.

BUT . . . something seems amiss . . . your pressures should not have varied like that. You should be feeding this machine with a pressure regulated water supply of ABOUT 2.5 bar (~35 psi). It has a balanced bypass valve on the pump that is designed to accommodate varying inlet pressures but 35 psi seems very reasonable.

December 29th, 2012, 7:12 am

Thank you gentlemen for such detailed responses. I appreciate you taking the time for me. I'm still lost. Nothing I see in my machine looks like the pictures you have posted. I too have found the tech manual, but see nothing that resembles the pictures. I have a suspicion that it is behind the back panel and not accessible through the top of the machine. Your thoughts are greatly appreciated!
Cindy

UPDATED: Added photos.

#5: Post by HB » December 29th, 2012, 8:17 am

The pump on a La Marzocco Linea is located outside the machine, usually near the water stopcock for the mains supply line. Most shops put them in the cabinet directly beneath the machine. As for the photos you wish to post, feel free to send them to me via e-mail.

By the way, if you don't have a service contract for your espresso machine, I recommend you consider one. It's a big investment and needs regular service. Adjusting brew pressure and temperature are easily handled by the shop owner, but it's only a matter of time before it needs descaling or repairs and that is best done by a La Marzocco certified technician.

#6: Post by HB » December 29th, 2012, 11:26 am

This is the rotary pump. The bypass valve for adjusting the pressure is on the right (see "acorn nut" and "pressure adjusting screw" in the previously posted diagram). Turn off the water supply per Eric's instructions and turn the adjustment in small increments (clockwise = higher pressure, counter-clockwise = lower pressure). And be careful not to unscrew it too far or you'll have water spraying out.

CrumbTopJava wrote:

December 29th, 2012, 11:49 am

ok...I'll give it a try after we close today! Wish me luck!

Thank you gentlemen!
Cindy

January 3rd, 2013, 2:27 pm

I DID IT!!! It is now Dispensing at just shy of 9 bars

Woo Hoo

Now...next question!!
What about the water temperature? What I have read is that the temperature should be between 190 and 200. My water is at about 170. When I pull the shot, the espresso is at around 140. Anything I can do about that?

Also what I have read is that the boiler temp is preset from the factory and we can not do anything about it. Other people seemed to have complained about the same thing with the LaMarzocco Linea.

Any thoughts???

Again...thank you for the previous help!!!!
Cindy