~5 bar spring in grouphead of cheap espresso machines - rotary pump effect?

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marteccino

#1: Post by marteccino »

So just found out that besides the notorious spring in OPV valve that will direct the flow back to reservoir after it exceeds certain pressure, there is another spring in group head of machines like delonghi or Starbucks saeco venezia that only opens when the pressure builds up to approx 5 bars. This too may perhaps explain why there is 3-5 seconds delay after switching on group head without portafilter, where more expensive machines seem to have instant flow after switch on.

I am not versed in various group heads and don't have other machine to compare it with, but isn't this spring mechanism that opens up with 5 bar to the puck an attempt to mimick rotary pump? And if it was changed for harder one that would only allow 9 bar buildup, wouldn't it act like rotary pump altogether? Even tho there might perhaps be some flow differences...but that's different topic. Most other machines with vibratory pump, I assume build pressure almost from zero or they too have some minimum pressure to reach before it introduces water flow to the coffee?
Or perhaps this spring might be a design to stop boiler drip when it's switched on steam mode and double serves the 5 bar initial opening as added benefit...?

Further more, same as with OPV spring, it looks like changing the spring for softer or different length results in different initial pressure that hits the puck, which may perhaps be more suitable for dimmer mods, because the standard spring again won't let water out untill it builds ~5 bar....softer spring may reduce that to 2-3 bars, but it seems never zero and that connects to my next question, how about other machines such as gaggia c, rancilio s, or ubiquotous e61, they let pressure build up from zero or too have some kind of minimum pressure buildup mechanism before they open the flow in group head?

JRising
Team HB

#2: Post by JRising »

The only purpose of that brew valve is to stop water and steam from escaping when not brewing... semi-auto and automatic machines need a brew-valve.

If it were not there the boiler would boil dry and all your steam pressure would just blow out the group rather than displacing the milk when trying to froth. It's simply the cheapest way to make a brew valve, a rubber stopper on a spring, so that the machine can be manufactured for a very low cost. It doesn't really do anything to improve the pump, nor the ramp-up of flow when brewing. It just ensures that the boiler doesn't boil dry.

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mrgnomer

#3: Post by mrgnomer »

From what I've read stock e61 machines at their OPV to 11bar. The OPV can be adjusted by screwing one part in or out to either compress or open the spring for higher or lower bar pressure opening.

With a rotary pump machine the OPV acts as a safety feature. The rotary pump itself is adjustable, usually set from 8 to 9 bar. A 11bar set OPV doesn't open with a lower bar set than the OPV.

I think with vibratory pumps you use the OPV to set the high end bar pressure. Stock vibratory pump output isn't adjustable.

Any other brew bar pressure limiting design is probably an engineering decision to favour a more forgiving extraction. 8 to 9 bar is considered a standard and popular but the extraction quality at lower pressures are favoured by a lot of people.

E61 groupheads by engineering design have a brief preinfusion low pressure flow. My heat exchange pump lever has a delay as well for the open inlet to fill the grouphead enough for flow to begin.
Kirk
LMWDP #116
professionals do it for the pay, amateurs do it for the love

marteccino (original poster)

#4: Post by marteccino (original poster) »

Yes I thoughts so too, but interestingly by doing so, it only starts pouring once it reaches certain pressure 4-5bars. Still I don't know if it's good or bad, but I wasn't familiar with this, I thought vibe pumps build up pressure from zero, that's why I suggested this behaviour might be similar to rotary pump effect that hits those 8 bars instantly.
Anyhow, cheap or not, I think some of these cheap machines deliver pretty much similar cup as any other more expensive ones, but misleading is only the form and how they go about it. Of course materials are incomparable, but what matters is which materials come in contact with water, and I can tell you, the water was much more contaminated from all iron, brass, chrome it touched on my previous e61 machine ad I could smell it.
And they all break and require service, cheap or not, and for me now, it's all about convenience and result in the cup, but am still researching
JRising wrote:The only purpose of that brew valve is to stop water and steam from escaping when not brewing... semi-auto and automatic machines need a brew-valve.

If it were not there the boiler would boil dry and all your steam pressure would just blow out the group rather than displacing the milk when trying to froth. It's simply the cheapest way to make a brew valve, a rubber stopper on a spring, so that the machine can be manufactured for a very low cost. It doesn't really do anything to improve the pump, nor the ramp-up of flow when brewing. It just ensures that the boiler doesn't boil dry.

marteccino (original poster)

#5: Post by marteccino (original poster) »

Looks like you are focusing on OPV valve, but I meant the small plastic valve in the brew head that's held by spring too and basically serves as resistance in order for pump to build certain pressure 4-5bars, and only upon reaching that pressure it opens the water flow to the coffee puck.
It does that whether portafilter is in grouphead or isn't, and every time I start the pump, there is a delay few seconds only after which water pours out. I wasn't aware of that before but it seems some of these machines with boiler above grouphead have it and I think by changing that spring you can modify the initial pressure that hits the puck, same way as rotary vs the gradual pressure on vibration pumps. For instance my previous generic e61 machine had instant water flow from group head without pirtafilter, so I think there wasn't any pressure build up, but I might be wrong.
So therefore I thought that when brew head only opens up the water flow once that spring is compressed and builds 4-5 bars, it might have similar effect on extraction as when rotary pump hits the coffee with almost instant 9 or whatever bar pressure. But again my analogyight be uninformed and I am just brainstorming. I think these small machines don't get enough credit, but every coffee enthusiast having big expensive machine should own also some $100-150 delonghi 3240 or similar in their garage, because I think it is unjustly overlooked due to its materials and size, but It heats up crazy fast, like really crazy fast, have stainless boiler and espresso is pretty good. Maybe not perfect, but the rest is achieved by modding...
mrgnomer wrote:From what I've read stock e61 machines at their OPV to 11bar. The OPV can be adjusted by screwing one part in or out to either compress or open the spring for higher or lower bar pressure opening.

With a rotary pump machine the OPV acts as a safety feature. The rotary pump itself is adjustable, usually from 8 to 9 bar. A 11bar set OPV doesn't open with a lower bar set than the OPV.

I think with vibratory pumps you use the OPV to set the high end bar pressure. Stock vibratory pump output isn't adjustable.

Any other brew bar pressure limiting design is probably an engineering decision to favour a more forgiving extraction. 8 to 9 bar is considered a standard and popular but the extraction quality at lower pressures are favoured by a lot of people.

E61 groupheads by engineering design have a brief preinfusion low pressure flow. My heat exchange pump lever has a delay as well for the open inlet to fill the grouphead enough for flow to begin.

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Jeff
Team HB

#6: Post by Jeff »

The flow rate into the basket, no matter the pump, will be limited by the pressure differential and the orifice size and shape. I thought the distinction between a "brew valve" and an OPV was pretty clear.

marteccino (original poster)

#7: Post by marteccino (original poster) »

Ok I am confused maybe due to my lack of knowledge, but I understood OPV valve regulates the pressure that pump produces. Let's say pump does 15, so OPV reduces it to 8-9-10, depending on settings or spring, and then there is this second valve in brew head that I understand has lower limit pressure point ~5 upon which it only then starts to flow, so it hits the coffee puck by my understanding with that 5BAR and from 5 bars it then reaches the upper limit of OPV usually 8-9. but that initial hit is already 5, where in comparison I thought in e61 it's like almost from zero that gradually hits the puck and then it builds up to whatever opv limit is and thats what extraction pressure is.
So to summarize it
Both my cheap machine extract with let's say 8-9 as per OPV, but the difference is that this second spring in brew head starts extraction already with built up 5 bar pressure where let's say e6q or machine without that spring starts from zero or some minimal pressure

Not sure I am explaining myself correctly

JRising
Team HB

#8: Post by JRising »

You're kinda part-way there.

Pumps create flow, not pressure. Pressure exists when there's restriction to the flow. The pump operates like a piston, a magnetic field "cocks" the piston back and a spring pushes the piston forward. The spring is able to push the piston forward with the force that equates to 15Bar+ at the pump outlet. The piston being pushed forward pushes the water ahead of it forward and out the outlet.

If flow is completely blocked off, the pump will stall (the spring won't be able to push anything forward). Because there's an OPV or expansion valve in the circuit, any time the pressure in the brew circuit exceeds 9 bar it will forcibly unseat the OPV, flow will escape there and the pressure won't be able to exceed 9 bar (The amount of flow out through the OPV and other escapes will be equal to the flow in from the pump, pressure won't continue to rise). Of course, there's also the spring loaded brew valve in the head, so any time pressure exceeds 5 bar it will forcibly unseat that and flow through the brew head. The actual pressure drop through the coffee-prep is still dependant on the size and coarseness of the coffee-prep ans the rate of flow. Just because there's 5 Bar pressure inside the boiler, before the brew valve, it's only atmospheric pressure in your kitchen, under the brew valve. Rate of flow through the prep determines the pressure differential. The spring loaded brew valves don't open like solenoid valves and suddenly expose the prep to boiler pressure, they're simply a precisely weighted check valve, like any other OPV.

And lastly: "Yes" the little, affordable espresso machines are capable of forcing hot water over a prep of ground coffee, all things considered, they can produce a very good espresso alongside the expensive shiny machines. The coffee prep matters, the grinder's quality matters much more (or at least in more ways) than the device moving the hot water.