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Thread: Over Pressure Valve OPV

  1. #1
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    Over Pressure Valve OPV

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Yes, Ive gone back and re-read OPV threads.

    http://coffeesnobs.com.au/YaBB.pl?num=1143118905/0
    http://coffeesnobs.com.au/YaBB.pl?num=1175171794/0

    Story:
    I have a Gaggia Espresso espresso machine. *Ive loosened on the OPV before because of what I think is a high-pressure problem of the "blonde gusher" pour. *The first 5 seconds of the pour are great with coffee beginning to dribble from every part of the naked portafilter, but then it changes to an instantaneous striped gush of espresso with a perfect (but too large) funnel, no squirting sprays, no voids. *The shot ends in about 15 seconds. *It starts to look similar to a coke-a-cola from the fountain.

    So, anyway, today I unscrewed the OPV fully, dislodging the spring and screw. *But no ball fell out. *I cut some plastic food wrap to fit the bottom of the portafilter basket to seal it up. *With the sealed PF in, I flipped the pump back on and *Bzz...zzzzz...zzzzzzzz...zzzzzz...zzzz.....PLOP! The stuck ball finally shot down into the water resevoir.

    I cleaned, then lubed the ball and threads with some olive oil (instead of petrolium jelly) and screwed it back in just a little bit. *This time the sealed PF forced water back into the resevoir, so the OPV is working now. *Pulled a shot with same grind and tamp as before and noticed the coffee sweeter than before, with more crema. *This is good!

    QUESTION:

    Shouldnt the OPV operate during EVERY SHOT on espresso machines with vibe-pumps? Since theyre rated much higher than needed for pulling shots.

    CHAD

  2. #2
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    Re: Over Pressure Valve OPV

    QUESTION:
    Shouldnt the OPV operate during EVERY SHOT on espresso machines with vibe-pumps? Since theyre rated much higher than needed for pulling shots.
    CHAD
    The OPV valve only opens when the pressure in the chanmer or line to which it is connected meets or exceeds the force needed to push the spring back and open the waste pathway. If your grind is too coarse or the distribution is poor, and the water can pass trough the coffee at a lower pressure than the set pressure of the OPV, then no, it will not open. Just because e pump is capable of producing 15 BAR does not men that it produces 15 BAR every time you turn it on.

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    Re: Over Pressure Valve OPV

    Hey, Randy, thanks for such a quick reply! *Im still confused, though. *Before this adjustment, the OPV has never operated on this machine. *I thought that my 17 bar pump would always produce more than 8.5-9 bar thats required for espresso, and therefore always have high pressure, hence operation of the OPV.

    CHAD

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    Re: Over Pressure Valve OPV

    I did a bit of enquiry and tinkering around with the OPV issue as I was concerned that I might not have been brewing at the right pressure and this is my finding:
    Prior to the OPV adjustment, I measured the OPV setting and it opened at 12 bar. I wasnt getting gushers but was concerned that the brew pressure was a little high. The taste wasnt bad by any means but i was looking to improve on it.
    Adjusted the OPV until it was about 9.5 bars now, didnt change the grind setting or tamping (the tamping pressure is pretty much constant as Im using the espro tamper). After this adjustment, I didnt notice any significant difference in the pour rate or taste. It didnt taste "sweeter" as was mentioned in some posts and Im half wondering if the "sweeter" taste coudl be more psychological than actual. Then again, the brain interpretes tastes and if one is happier with the taste, then let it be.
    My conclusion the whole exercise is that given the OPV pressure is really dependent on the back pressure exerted back by the tamped coffee, even when my OPV was set at 12 bars, my tamping and grind (and dosing) was pretty much providing a back pressure of less than 9.5 bars anyway.
    If I had to guess, even when your OPV was stuck, I reckon your brew pressure wouldnt have gotten near as high as 17 bars unless you were putting your whole weight behind the tamp and the grind size to fine...

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    Re: Over Pressure Valve OPV

    Quote Originally Posted by seedlings link=1224528430/0#2 date=1224533608
    Hey, Randy, thanks for such a quick reply! *Im still confused, though. *Before this adjustment, the OPV has never operated on this machine. *I thought that my 17 bar pump would always produce more than 8.5-9 bar thats required for espresso, and therefore always have high pressure, hence operation of the OPV.

    CHAD
    The small vibratory pumps produce a pretty small volume of water. To be able to reach their maximum pressure they need some pretty good resistance at the output end somewhere. Think of it like holding your thumb on the end of a garden hose. The more the resistance from your thumb the closer you get to reaching the maximum pressure that the hose can deliver.

    If you think of the packed coffee as your thumb you begin to get the idea. If the coffee is coarse ground or there is not enough of it or there is a channel that the water can get through easily, the pump does not have to work that hard to cause the water to flow so it will not reach maximum pressure. If you packed the coffee really tight with a Turkish grind then the pump will approach or reach it maximum possible force... either that or it will blow a seal, pop off a hose or do some other damage like overheat the pumps windings or burn out the diode in the pump.

    Now this brings up another point, and an important one that I have never thought of previously.... Stick with me on this one... Its time to play... "What If?"

    What if....
    1 - the OPV is set a bit too high at the factory
    2 - the user never chokes the machine using a too-fine grind
    - or -
    the machine has a crema enhancing device that allows the
    user to use a too coarse grind all the time?

    In either of those situations the OPV may never have to open, and so, over time, it can corrode/rust/get gunked with minerals.. whatever. It is now rendedered non-functioning— it cant open.

    Now... Time goes by, our user advances his/her/its skills and decides to uprade grinders and go from the Cuisinart to a Mazzer SJ. Finally able to grind fine enough and consistently enough, the machine is now called upon to really go to work. A beautiful, thick stream of espresso begins to flow and after about five seconds it becomes a blonde gusher (no wise cracks.. this is serious!).

    Our user now thinks, "What the FireTruck just happened!?" Tries again and the same result. Adjusting the grind only results in either thin, watery under-extractions or the gushers described above. Our user now assumes that there is something wrong with their new grinder. "If I could get good pulls with the Cuisinart, there must be something wrong with this stupid, expensive Mazzer." In this case, ignorance is NOT bliss.

    It would not occur to the user that the problem lies in the over-pressure relief valve (OPV). What is the solution? BACKFLUSH REGULARLY! By doing clear water backflushes on a regular basis (even once a week) will force the machine to open the OPV, forcing the seal (whatever it might be) off its seat and thereby "exercising" the device so that it has a far smaller chance of becoming stuck.

    Now if the machine has a pressure gauge, and the user is paying attention, then there should be little doubt as to the problem. Happened to me when I first got my VBM DS as it had an OPV spring that was out of specs. I replaced it (furnished by the US importer) and all was well. But had I not had a pressure gauge on the machine (or at least a PF gauge of some sort) I think I would still be chasing my tail trying to find a solution.

    Hope that helps clear things up.. a a bit.

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    Re: Over Pressure Valve OPV

    Quote Originally Posted by NewToEspresso link=1224528430/0#3 date=1224542213
    ...
    My conclusion the whole exercise is that given the OPV pressure is really dependent on the back pressure exerted back by the tamped coffee, even when my OPV was set at 12 bars, my tamping and grind (and dosing) was pretty much providing a back pressure of less than 9.5 bars anyway.

    If I had to guess, even when your OPV was stuck, I reckon your brew pressure wouldnt have gotten near as high as 17 bars unless you were putting your whole weight behind the tamp and the grind size to fine...
    I think you have made some excellent points.

    The only way to be sure what is going on with the OPV is to pull the return line (if the machine has one) and watch the flow from it while an extraction is taking place. And/or, insert a blind filter and see what the gauge reads. The valve is not binary and may even trickle a bit below the maximum pressure depending on how close that is. For the life of the machine it is a good idea to have it properly adjusted, if for no other reason than when you are backflushing.

    One thing to be aware of is that the pressure gauges that are used on a lot of machines are pretty basic and their accuracy is certainly suspect. Cheap gauges sell for $8 to 15 or so. Quality ones of reasonable accuracy can be $80. Guessing at the numbers, but it would certainly add a lot to the price of a machine to be equipped with quality instruments.


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    Re: Over Pressure Valve OPV

    OPV 101 class was in sesson today! Bravo!

    Im beginning to see clearer now. At first theres a thick forest. Then I could make out a little path entering the thick forest. Then I notice there are mostly Cedar trees, with some White Oaks sprinkled here and there. Now, I see birds nesting and deer prancing in the meadows beyond the first few trees.

    What youre saying is the back pressure could be potentially infinity, but if I grind distribute and tamp well, the pressure will only make it up to +/-9 bar. I get it now. The potential created by the pump is flow current limited by the resistor of the puck.

    Dont look for my puns to be at a club near you soon.

    Does the puck present a constant resistance? Could it be that the boiler pressure levels off at 9.5 bar for 5 seconds, but back pressure builds up to 13 bar behind it, followed by the gush?

    Also, the "Gaggia Espresso" model that I have does not have a 3-way valve, and I thought backflushing was advised for machines with a 3-way valve. I guess youre really recommending an OPV flush, though, which is good advice.

    He can be taught:
    CHAD


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    Re: Over Pressure Valve OPV

    Now youre going to 102 territory. Without a pressure gauge in line with the pump (that comes standard with most commercial machines), it is difficult to really measure what your brew pressure will be. The OPV is really only a pump protection device, not so much a brew pressure control device. Unlike steam machines like the Breville Bar Italia, the boiler pressure doesnt provide the brewing pressure, that is provided by the Ulka pump pumping the water. The boiler pressure provides the steam pressure though when you activate the steam switch in a dual purpose single boiler machine like the Gaggia.
    The Ulka (vibratory) pump is capable of pumping out water at 15 bars but the higher the pressure, the less water it will pump out. There is a graph in the ulka website showing this. But again how water actually gets pumped through the coffee puck and how much escapes through the OPV is a bit hard to determine. If you follow the Ulka graph, at 9 bars the pump pumps out 260ml per minute. In a 25 second shot, that comes to 108ml. Dont know much of that is trapped in the puck saturating it, dont know how much of that which comes out are the oils that make up the crema... I suppose thats why eventually the advise is: go by your taste.
    As a starting point, aim to get 30ml shot in 25-30 seconds, and tweak from there according to taste.

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    Re: Over Pressure Valve OPV

    The resistance to the flow of water can be "infinite," or total, or whatever the correct term is. Its the same as when you use a blind filter.

    The pressure between the pump and the puck will be roughly the same throughout the system most of the time, once it is all filled with water. if there is air in the boiler it could affect that to a small extent, and water flowing through a pipe will suffer from pressure loss due to friction, but the difference should be minimal. There are exceptions, such as with teh E-61 brewhead which builds pressure at the coffee more slowly than other systems, and some of the newer computer-controlled machines will build the presssure the same regardless of the coffees grind and tamp compaction, but neither of us can afford such a machine. ;)

    If a machine is not equipped with a 3-way valve it should not be backflushed. Additionally, there were some machines with a 3-way valve located at the pump side of teh boiler (iirc) and these should not be backflushed either. Any machine with a 3-way valve located between the boiler and the brwhead should be backflushed. I have some very detailed articles and lessons on my website related to the 3-way and backflushing.

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    Re: Over Pressure Valve OPV

    Quote Originally Posted by NewToEspresso link=1224528430/0#7 date=1224557608
    Without a pressure gauge in line with the pump (that comes standard with most commercial machines), it is difficult to really measure what your brew pressure will be.
    Quote Originally Posted by Randy G. link=1224528430/0#8 date=1224559108
    The pressure between the pump and the puck will be roughly the same throughout the system most of the time, once it is all filled with water.
    NTE or Randy... There is plenty of room between the OPV and the boiler on my Gaggia. If a pressure gauge were installed there, would that be an acceptable place, and provide helpful information? Beyond that, would the gague just vibrate back and forth when as the pump vibrates, providing useless information?

    Pump -> OPV -> Pressure Gauge -> Boiler -> Brewhead

    CHAD

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    Re: Over Pressure Valve OPV

    Quote Originally Posted by seedlings link=1224528430/0#9 date=1224595540
    NTE or Randy... There is plenty of room between the OPV and the boiler on my Gaggia. If a pressure gauge were installed there, would that be an acceptable place, and provide helpful information? Beyond that, would the gague just vibrate back and forth when as the pump vibrates, providing useless information?

    Pump -> OPV -> Pressure Gauge -> Boiler -> Brewhead
    Gday Chad,

    Just so happens that Im still up and about at this late hour here in Oz and maybe I can help out a bit.... ;)

    Fitting a Tee-Off downstream of the high pressure line from the OPV IS an acceptable place to connect in a Pressure Gauge. You might notice a slight buzz of the indicator needle with the line under normal operating pressure but at 60Hz it should be barely discernible and of no consequence. Most gauges of this type will damp out high frequency fluctuations and if you opt for a glycerine-filled gauge, the damping effect should be almost total.

    Something worth mentioning and something that Chris Natoli has observed with all the machines that he has bench-tested over the years, and referred to in passing by Randy above, is that there will be measurable losses in a dynamic system such as this. As a result, Chris has determined that a pressure setting of 9.5 Bar upstream of the Group, will result in an almost perfect 9 Bar at the PF Basket when pulling a shot. Ive never carried out this test myself but Chris findings are more than good enough for me. 8-)

    Anyway mate, hope some of the above helps you out. All the best, :)

    Mal.

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    Re: Over Pressure Valve OPV

    There is plenty of room between the OPV and the boiler on my Gaggia. *If a pressure gauge were installed there, would that be an acceptable place, and provide helpful information? *Beyond that, would the gague just vibrate back and forth when as the pump vibrates, providing useless information?

    Pump -> OPV -> Pressure Gauge -> Boiler -> Brewhead
    When adding a pressure gauge you would want the gauge to be plumbed as close to the brewhead as possible, but you are limited by your ability as well as the machines design and the amount of room you have to work. For example, when the brewhead if mounted to the boiler, you could drill and tap the boiler for a fitting, or drill and tap into the brewhead itself, but the amount of effort it would take is great, and the benefit over mounting it in the supply pipe to the boiler is minimal. So plumbing it anywhere after the pulp, and preferably after the OPV should be fine.

    When choosing a pressure gauge, get one that is oil filled. These are specifically made to mount in systems that either have fluctuations as in an espresso machine, or when mounted to vibrating surfaces. Also, get a good one. If you are planning on punching a hole n the face of your machine then you want one that is highly functional, easy to read, long-lasting, and as accurate as possible. Also, when choosing a range, try to find one with the desired pressure as near the center of the range as possible.

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    Re: Over Pressure Valve OPV

    How do I know if its oil / glycerine filled? *On this page, http://cafeparts.com/listCategoriesA...CategoryID=780
    How about the "Pump Pressure Gauge Gaggia Ele 49mm"
    Or the "Pump Pressure Gauge Gaggia Ele 52mm"

    Or, for $8 less, theres
    http://www.espressoparts.com/product...ure_Gauge.html

    Will any of these work?

    Ive read some threads about drilling out the group for a pressure gauge. *If* I were to do that, where on this machine would be a good spot? The water inlet is in the block at the bottom of the boiler.





    CHAD

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    Re: Over Pressure Valve OPV

    None of those looked like they were oil filled. When they are, the case is literally filled with oil and there is a large bubble at the top of the face. Your concerns abut dampening are real, and another way to deal with that is to run a very small diameter of copper pipe between the gauge and the source. The narrowness of the tubing will effectively dampen the pulses. The VBM uses that method. Another way is to put a valve in between and just crack it a tiny bit. Yes, this slows the response a bit, but not enough to matter.

    The oil filled gauge I got was a surplus item and not originally intended for espresso machine use. I hooked it to a PF.

    Quote Originally Posted by seedlings link=1224528430/0#12 date=1224613337
    How about the "Pump Pressure Gauge Gaggia Ele 49mm"
    Or the "Pump Pressure Gauge Gaggia Ele 52mm"
    Thats the one I thought looked best. The very wide flange will hide cutting mistakes better. ;)

    Ive read some threads about drilling out the group for a pressure gauge. **If* I were to do that, where on this machine would be a good spot?
    I give up... Where WOULD be a good spot? ;)


    Since I do not know that machine I cannot recommend exactly where to do that. Unless you find specific instructions on how and where to drill the boiler, that would be my last choice, particularly since it is aluminum wit an embedded heating element. My first choice would be the most easily reversed or repaired. That would be in a water line that can be easily disconnected at both ends and replaced. if the machine is fed with the teflon type of water lines, that would be my first choice. If you do that, you could even used an extra-long length and put the gauge in an external box so that you dont have to drill the case (if there is even room for a gauge in there)...

  15. #15
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    Re: Over Pressure Valve OPV

    Quote Originally Posted by Randy G. link=1224528430/0#13 date=1224623648
    Your concerns abut dampening are real, and another way to deal with that is to run a very small diameter of copper pipe between the gauge and the source. The narrowness of the tubing will effectively dampen the pulses.
    This would need to be bordering on "capillary tubing" such as that found feeding fridge evaporator coils from the compressor.

    To be honest though, Ive never found 50Hz pulses to be a concern with most industrial gauges Ive tried and the effect would be even less with a 60Hz supply. If you have a hydraulics supply & service store near you somewhere Chad, I imagine you would be able to look at a few gauges (glycerine and air damped) of the right size and scale that would do the job quite well. You can get them with fascias in polished brass, chrome-plated, nickel-plated, stainless steel and painted and with dial faces in either black or white. They wont have a high-lighted section between 8.5-9 Bar though but the better overall quality of the gauge should make up for that. ;)

    Cheers :),
    Mal.

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    Re: Over Pressure Valve OPV

    I think this will work! *Mal, the needle does bounce around a little. *Found this non-oil gauge for only $6 at a local tractor supply store, replacement gauge for pressurized tanks for spraying water/chemicals. *Its in PSI... 9 bar = 130 PSI. *Adjusted the OPV to get about 150PSI, but havent tried shots yet.




    Very short video:
    http://www.youtube.com/watch?v=HCGnYGts3NI


    Wound some copper tubing around the boiler to preheat the water. Thread with more info:
    http://www.homeroasters.org/php/foru...thread_id=1037

    Thanks, all!
    CHAD

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    Re: Over Pressure Valve OPV

    Doesnt look too bad installed. 135 PSI = 9.3 bar.

    CHAD


  18. #18
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    Re: Over Pressure Valve OPV

    Nice job Chad, [smiley=thumbsup.gif]

    Will be a great tool re: instant feedback on your dose, distribution and tamping (after taste that is).

    If you know someone who works in the Instrumentation Trade, you may be able to source a new gauge dial that is graduated in Bar. Or, you could remove the cover glass, the dial and identify the section referring to 8-10 Bar, then reassemble. Not really necessary but means that you know exactly whats going on at a glance.

    All you need now mate is a Brew Water Temperature gauge and youre Smokin.... 8-)

    Mal.

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