Noisy/faulty OPV and use of OPV in general

[dsc]

Hi everyone,

Recently I've been having several problems with my Andreja and think that one of them is the OPV. Two weeks ago the machine started making a weird high frequency noise when the brew pressure goes up to around 9 bars. I know that the OPV is set to 9.5bar so I'm guessing that the noise is simply generated by the opening valve, as the machine goes silent again after a few seconds. Could that be it?

In addition usually during a shot the stream coming out of the PF (not a naked one but with the spouts removed) is pulsating from around the 15s of the extraction until the very end. It starts quite slow, dripping and forming a thin 'tail', but when it gets thicker a bit it simply starts flowing inconsistently like it was choking or spitting out the coffee. Could that also be somehow connected with the 'faulty' OPV? Maybe the spring inside is a bit worn out or there's not enough lubrication, so the whole thing simply jams slightly while dropping below 9bars and going above it again.

On top of that all (like it wasn't enough:)) I was curious whether using the OPV to restrict brew pressure is really the way to go. Factory setting for the OPV is 12bars as most of you know, and this is for both cheaper and more expensive machines (pro HB ones). I know that the companies that produce those machines, at least the more HB oriented, are aware that most users turn them down to 8.5-9bars, although they still leave them set to 12 bars when they leave the factory. Have you ever wondered why they do that? I mean maybe the OPV is not supposed to be used for brew pressure regulations? A friend of mine was doing some tests that involved sticking a pressure gauge in a HX installation and came to a conclusion that the OPV is mainly used to release pressure build up when the water left in the tubes is heated and pressure raises. The OPV opens so that your machine is not blown up to pieces by that heated water. I started thinking about his discovery (which is pretty obvious) and wondered what would happen if I was to turn the OPV up to 12 bars again and control brew pressure simply by grind. When the pressure is too low, change the grinder setting to finer, when it's too high switch to a coarser grind. This of course complicates the whole routine, as you have temperature, pressure and volume to look at and I was curious whether it's possible to achieve an optimum of some sort to get 9bars of pressure, 60ml of espresso from a double basket, brewed at 90*C or so. The last thing is easy to achieve with the use of cooling flushes. Volume is also quite easy to achieve on it's own, but because it is connected with grind settings and that is connected with pressure, it gets a bit harder. I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV? I'm pretty sure it depends on the coffee (freshness, type) but even if that element is spot on, it might be a tricky task. You can always play with the dose changing that to further affect the output but that complicates things further. I thought of this method which might make it possible, although it can cause channeling with lower doses or higher pressure:

- turn your OPV up to 12bars
- dose normally, tamp, lock and brew checking the brew pressure and volume
- if brew pressure is above 9bars, grind coarser and check volume again
- if volume is too high compensate by dosing a bit more, so the flow is slower (although this might push the pressure a bit up)
- if volume is too low, dose less

You might need to correct your grind settings after changing the dose.

I'm curious if you can achieve anything drinkable with that kind of approach. Anyone ever tried something like this?

Cheers,
dsc.

[Randy G.]

Try adjusting the valve down to a much lower pressure- like around 7 or 8 bars, grind accordingly, and see how the machine reacts to that. Maybe even disassemble the valve to be sure that it is not caked with hard water deposits or other debris that could be affecting its operation. Examine the piston or sealing area (I do not know that machine) for signs of wear or corrosion, etc.

I would question the accuracy of your friend's gage. 12 bar is high and I do not think that you would find that many machines all set that high. Fooling the OPV would be difficult because the resistance to the flow of water can change during the extraction. That is just a guess. Also remember that if you are comparing the machine's gage which is plumbed to the internal pressures to the one mounted to a portafilter, you are measuring two different pressures.

The OPV would not (should not) be opened by internal pressures when the machine is idling. The simple heating of water in the boiler will not create the pressure that you get from the pump.

[lsf]

My Andreja started making exactly the same noise 3 months after I bought it. I brought it back to the shop twice and was told twice that my machine was ok and nothing was wrong with it. My machine still makes that noise and I'm now trying to convince myself that it's normal... I respoke to the seller and he offered me to come back and make some coffee with them to show them how the machine really behaves since they don't seem to find the problem.

I'm wondering if anybody I's going to find a solution...

[dsc]

Hi,

I will definitely disassemble the valve today to see what's going on. I'm pretty sure the noise is caused by the OPV, but I'm more concerned about the pulsating flow than the noise.

As for the pressure build up you would be amazed, but it does get to pretty high values. See this clip:

http://youtube.com/watch?v=nhg8mAhXfIM

The additional manometer (which shows the build up and you can clearly see when it opens) is installed in the HX. Pump pressure is not the only cause of OPV activation.

Cheers,
dsc.

[hbuchtel]

(...) This of course complicates the whole routine, as you have temperature, pressure and volume to look at and I was curious whether it's possible to achieve an optimum of some sort to get 9bars of pressure, 60ml of espresso from a double basket, brewed at 90*C or so. The last thing is easy to achieve with the use of cooling flushes. Volume is also quite easy to achieve on it's own, but because it is connected with grind settings and that is connected with pressure, it gets a bit harder. I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV? I'm pretty sure it depends on the coffee (freshness, type) but even if that element is spot on, it might be a tricky task. (...)

I really like this question! In my limited experience with it, a grind/dose that 'naturally' produces ~9 bar flows really quickly... I can't remember anything about the taste though... Something to play with this weekend!

Your question also reminded me of this thread

Henry

[JimG]

.... I mean is it at all possible to set a grind setting which would give you 60ml of liquid brewed at 9bars without touching the OPV?

Let's say you add the requirement that the extraction takes 25 seconds (approx. 2.4 ml/sec, ignoring the water absorbed by the coffee).

As I see it, without an OPV you can use the grind setting to control the pressure (9 bar) or the flow (2.4 ml/sec). But not both.

For a given voltage, the pump is going to discharge a specific flow at a specific pressure. For instance, the curve for the common Ulka vibe pump shows a discharge of around 4.3 ml/sec at 9 bar. So if this is the pump you have in your machine, and you want to extract 60 ml in 25 seconds, then your OPV will have to shunt the excess flow (1.9 ml/sec in this example) back to the reservoir.

In this particular example, the correct OPV setting would be the one that shunts exactly 1.9 ml/sec at 9 bar. And this is probably not exactly the same OPV setting that shunts 4.3 ml/sec at 9 bar, which generally means your so-called static pressure reading with a blind filter should be higher than the desired brew pressure.

To avoid the need for adjusting the OPV, and to control both the pressure and the flow using your grind setting only, then you must have a means of altering the basic pump discharge curve. For a vibe pump like the Ulka, this probably means controlling the voltage.

Jim

[Beezer]

The OPV on my Anita also squeaks a bit. This seems to be a common problem with the OPV used in Quickmill machines. See this video of pulling a shot. The pump noise is totally drowned out by the squeaking OPV.



I just spent the last couple of days readjusting the OPV to try to get rid of the annoying squeal. After tuning it up from 8 bars to 9 bars, the squeal is almost gone. Now it squeaks just a bit when it comes up to full pressure, then the machine is almost silent. Much more pleasant.

As for the pressure variations, I would expect those to have more to do with distribution problems than the OPV. But I'm not sure.

[dsc]

Hi,

well first test are not promising. I turned the OPV up to 12bars and no matter how I grind the coffee the OPV still activates.

Jim: yes that's all true but if you add a restriction in form of coffee the flow is lowered isn't it? Otherwise even with the OPV opening at 9bars you wouldn't be able to get a ristretto because it would flow with 2.4ml/s and I believe a ristretto is much slower (well at least at the start).

Beezer: that's exactly the sound I was getting until today when I took the OPV apart, cleaned it in some lemon juice (had no citric acid) and put it back together (lubricating the ends of the spring with some silicone grease).

Anyway I'm curious if anyone else tries it.

Cheers,
dsc.

[JimG]

Jim: yes that's all true but if you add a restriction in form of coffee the flow is lowered isn't it?

Total flow is not lowered, just the part that goes through the coffee.

With an OPV set at ~9 bar, the total flow leaving the pump probably stays about the same regardless of the coffee resistance. But as you grind finer and/or dose more, then a larger fraction of the flow gets shunted back to the reservoir, leaving a smaller flow to go through the coffee.

With no OPV, the total pump flow drops as a result of the pressure increasing, which moves you "up" on the pump curve. You can adjust grind/dose to move anywhere you like along the pump curve -- but you gotta stay on the curve.

Otherwise even with the OPV opening at 9bars you wouldn't be able to get a ristretto because it would flow with 2.4ml/s and I believe a ristretto is much slower (well at least at the start).

You still get a ristretto because more flow is being shunted through the OPV and back to the reservoir. Total flow might still be around 4.3, but now only 1.2 ml/sec (for example) goes through the puck, while the remaining 3.1 ml/sec goes back through the OPV to the reservoir.

Jim

[cafeIKE]

I just spent the last couple of days readjusting the OPV to try to get rid of the annoying squeal.

An OPV should not squeal. 15 minutes and a dollop of Lubrifilm is all it takes to make it silent.

Site sponsor Stefano's Espresso Care sells Lubrifilm in 1oz tubes, essentially a lifetime supply.

[erics]

An OPV should not squeal.

For sure, you are correct. Unfortunately, the OPV on the QM machines is a little different than others. All (well, at least within the past couple of years) QM machines equipped with vibe pumps have their OPV on the outlet side of the hx. When the flow of hot water goes past the OPV in just the "right" amount at just the "right" opening of the OPV the combination of the valve, the spring, the pump flow characteristics, and the mfg tolerances on the assy, together with any scale present inside exacerbate any vibration present and hence the squeal.

I can easily duplicate the effect on my laundry room faucets by reducing the flow to a small stream. Perhaps the quality of the faucet enters into the equation.

How to fix:

As dsc has done, soak the OPV valve internals in lemon juice, citric acid, vinegar, etc. It might not be a bad idea to remove the housing and soak it also but be advised that the straight threads at the OPV inlet need some form of sealant (loctite, teflon tape, copper washer, etc.).

Chris Coffee sells new inserts for the valve and anyone with a QM machine should add these to the "to buy" list along with an o-ring for the adjusting nut and food grade lubricant for same.

Reinstall the OPV and attach hardware store tubing to the OPV outlet. Plug the existing machine's OPV tubing line with a golf tee. This makes OPV adjust easy as you are not kinking and untwisting the PITA original short hose.

Run the pump with a blind filter in place and adjust the OPV with the heating element disabled. What pressure do I adjust to? Everybody has their favorite but I would suggest 9.0 bar. IIRC, this should give about 8.5 bar at the puck and a little less when the element kicks in during normal ops. If it squeals, make it 9.1 or 8.9 bar.

Reattach all original hoses, undo the disabling of the heating element and pull some real shots with the covers off. Readjust as necessary - hopefully NOT.

[Beezer]

Thanks for the tip Ian. I may have to order some of the Lubrifilm. That squeal is really annoying.

[cafeIKE]

QM machines equipped with vibe pumps have their OPV on the outlet side of the hx.

Coolish fresh water is not going to scale the OPV or wash out the lube.
Why feed hot water back into the tank. Enhanced operation in Siberia?
Any 'sensible' idea why they do this?

Seems like the perfect opportunity for another brilliant Eric Svendson kit.

[erics]

Seems like the perfect opportunity for another brilliant Eric Svendson kit.

Like this?

[mhoy]

Eric: Please say that's a quiet rotary pump that will drop into my Anita....

[erics]

Fortunately, no.

It is, purportedly, a very quiet and high quality vibe pump - the FOT 1106 - see above performance curves. It will be the subject of a separate post in a month or so.

[JimG]

It is, purportedly, a very quiet and high quality vibe pump - the FOT 1106 - see above performance curves. It will be the subject of a separate post in a month or so.

The cost to revise all of the "15 bar pump" marketing materials will doom it to failure.

Jim

[erics]

DSC -

I watched your video and noticed that your Andreja is an older model (?). Perhaps your hydraulic system is a little different than the current version, e.g. do you have the little bleed valve installed onto the snout of the Ulka pump and where does your brew pressure gage pick up its measurement? Is your machine even equipped with an Ulka pump?

[dsc]

Hi everyone,

When it comes to the way how an OPV works I understand it this way:

- coffee in the basket acts as resistance, sort of like a small hole that restricts the flow

- the pump it self, based on its characteristics, gives a certain flow rate at different pressures, for example 240ml/min at 9bars

- if the OPV is set to 9bars the pressure in the installation won't go above that value, well because simply the valve will open at pressures > 9 bars

- so basically 9 bars is the max we can get in the installation, meaning that with the OPV opening the flow rate will be what the characteristic shows = 240ml/min, which is 4ml/s

- with 4ml/s and nothing in the path of the water we would get 100ml in 25s

- well we all know that we get values even lower than 60ml in 25s (ristrettos for example), so I'm guess that coffee acts as resistance, lowering the flow, absorbing some of the water, etc.

Hope this makes sense:)

I turned the OPV down to 9bars again and it's still silent, so I guess that disassembly helped. I am however still having pulsating flows:|

Oh and as for the voltage of the pump I doubt it would change anything, as the vibe speed is dependant on the frequency (vibrating with 50Hz). It might be however possible to lower the flow rate by installing a flow restrictor, or making the existing one a bit smaller (sticking a small wire in the whole).

Eric -

you mean the video with the additional pressure gauge that shows how the OPV opens after a flush (the one I placed in this topic)? if that's the one you are talking about I have to clarify that it's not my machine and not my video:) That's not even an Andreja:) As for my machine I believe it's the newer model, it has got a CEME pump which is very loud and blue. I tried disassembling it once but there seems to be a metal clump around the pump's case which makes it impossible to remove. I will try to upload some picture of the inside so you can see how it's connected.

Cheers,
dsc.

[erics]

Hope this makes sense:)

Reread Jim Gallt's explanation to you of how the OPV functions in an espresso machine. It is correct and to the point. You could also do an HB search on "OPV" and while this would return many threads, the appropriate ones are easy to pick out. All of the manufacturers that produce pumps for our espresso machines provide pump performance curves that depict how an average production pump will perform with NO regulating/relief/bypass valve in the system. All other factors being reasonably equal, you can change the grind and/or dose all you want and that will NOT change the flow from the pump but will, of course, change the flow through the coffee puck.

Changing the voltage applied to the pump will alter the flow - look what happens to the pressure when the heater element kicks in and voltage available to the pump drops down about 5 volts. You may not experience that because you're operating at ~230V and your wiring is sized for 120V. Do an HB search on "Variac" and you'll find some posts by Jim Schulman wherein he described the application of a Variac to control the Ulka pump.

The flow characteristics of the CEME pump may be quite different than that of the Ulka - hence A need for the OPV to compensate for different pumps. Look at the rather dramatic difference between the Ulka and the FOT 1106. The OPV in a machine that has the FOT could easily "take a nap" and probably remain closed its entire life. And now that I see where CEME has purchased Ulka - http://www.cemeeng.com/index_en.htm , espresso machine pumps might have further developments.

Your pulsating flow MIGHT be as a result of a faulty "bleed valve" (if so equipped) on your pump/machine.