Does a vibe pump fail suddenly? - Page 2

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cannonfodder
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#11: Post by cannonfodder »

another_jim wrote:You can get relief in two ways:

1. Finding an outlet close to the circuit breaker panel (not always possible). If you are really incensed by this, run a 12 gauge extension cord to a close outlet.
2. Replacing the existing 18 (!) gauge power cord of the machine with a 12 gauge cord (the wiring on Italian machines is never changed compared to the 220 models -- a very bad practice, albeit within code, since they spec very fine wire gauges for "within panel" wiring). This fix got me from 1/2 bar down to about 1/6th bar change during heating cycles.
Interesting. My machine is on a very low use circuit but it is at the end of the loop, about 38 feet from the breaker box, 20 amps I believe. I will have to check the power cord gauge next time I crack the case.

I believe pressure stability/adjustability will be the next target of the market. PID's have really tightened down thermal stability, but if you cannot control the pressure, your returns are limited. Some days I can pull incredible shots using my lever machine, part pressure control, part luck (Probably more luck than skill) :oops: .
s_m_k wrote:I don't doubt that you've seen this, but it doesn't make sense to me. I thought that pumps typically operate well above the required pressure (15 bar or so) and the OPV regulated down to the "working" pressure.

Is this a false assumption? After all, I am a newbie.
Jim would be better than I at explaining, he is the process controls master. Regardless of how much pressure your pump can generate, it requires X watts to operate at that level. If I am supplying a pump with X watts, then suddenly turn on a hair dryer in the circuit in front of the pump, that device will pull Y watts out of the circuit. So if my 500 watt pump (just grabbing a number out of the air) pumps at 9 bar at 500 watts, but I drain off 250 watts of power on that circuit, my pump now only has 250 watts to work with, so it slows down. Now my 9 bar pump can only muster 4.5 bar.

My new machine (check out the Faema rebuild thread) is a rotary pump 220. The machine only draws 13 amps, has a 20 amp rated power cord, and I am supplying that with a 30 amp circuit (10/3 wire), so power should not be a problem any longer.
sunnyu wrote:cannon,
Would be most interested to read the results. Thanks.
And the answer is....

From a cold machine (no heat induced line pressure) with no portafilter I fill a Pyrex one cup measuring cup in 29 seconds. Keep in mind that the heating element is on while the machine pumps, so it may be a second quicker with that off. But that should be close enough for government work.
Dave Stephens

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another_jim
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#12: Post by another_jim »

s_m_k wrote:I don't doubt that you've seen this, but it doesn't make sense to me. I thought that pumps typically operate well above the required pressure (15 bar or so) and the OPV regulated down to the "working" pressure.

Is this a false assumption? After all, I am a newbie.
Unfortunately, the OPV is not a perfect device, but depends on the inlet pressure. This is why if one sets it at 9 bar against a blind filter (15 bar inlet pressure from the pump), it'll drop to 8.5 or so bar at espresso flow rates (12 bar inlet pressure). The same applies when there's a voltage drop because the heater kicks in.

In control terms, the OPV does operate on feedback (the spring balances at the pressure set). However, it works like a pure proportional controller without integral action, so that changes in the pump (input) pressure create the typical proportional band error.

s_m_k

#13: Post by s_m_k »

Of course! It acts like a single-stage regulator, not compensating for drops in inlet pressure.

Thank you for the insight.

sunnyu

#14: Post by sunnyu »

There is a world of difference between 500watt hair dryer vs a 50watt vibe pump. The latter is virtually no load compared to the 1400watts your heating element pulls. The drop in pressure and the element kicking in could be coincidental. Besides the pump operates on a different principle, one of revolutions and not direct torque. Your hypothesis could be true if the output of the pump was only 9bar, but it is 40% more and a drop in current should not effect that adversely.

Dan, replacement is not the issue but knowing when and if to spot early failure. For instance regular alkaline batteries are not linear, they gradually lose performance, thus to keep output optimal one must replace long before they completely die. i have been trying to ascertain that about vibe pumps. Is there a gradual decline that should be observed and the pump replaced or wait till there is no flow?

So far i have been unable to see any obvious wear parts inside the pump. The piston is not a tight fit by design. However if it is the springs then the OPV should be the first to go but remedied via tightening????? :?

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another_jim
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#15: Post by another_jim »

sunnyu wrote:There is a world of difference between 500watt hair dryer vs a 50watt vibe pump. The latter is virtually no load compared to the 1400watts your heating element pulls. The drop in pressure and the element kicking in could be coincidental. Besides the pump operates on a different principle, one of revolutions and not direct torque. Your hypothesis could be true if the output of the pump was only 9bar, but it is 40% more and a drop in current should not effect that adversely.?
I'm not sure I get you. The pressure drop on espresso pumps when the heater kicks in is quite universal; it happens to good pumps, and has nothing to do with the OPV or anything else inside the machine. The pump is electrically in parallel with the heating element, and both are in series with the wiring to the circuit breaker. The heater is 8 to 15 ohms, depending on the wattage (at 110), while the house wiring can easily amount to to 1.5 to 2 ohms if the run is long. The use of thin wires meant for 220V (4 times the resistance in the element) doesn't help either, and I urge people who have this problem to rewire the entire run from espresso machine plug to the heater with 12 gauge wire.

If the house wiring is 2 ohms (worst case) and the heater is 8 ohms (worst case -- 1500 watts), then the voltage can drop from 120 to 96 volts for the entire machine, including the pump. This will mean the pump pressure drops dramatically (about 3 bar). Mostly, it's a bit less dramatic, but drops of 5 to 10 volts, and 1/4 to 1 bar, are pretty much unavoidable depending on the state and length of your home's wiring.

You can confirm this for yourself by playing with the voltage drop calculator on Powerstream's wire size page:
http://www.powerstream.com/Wire_Size.htm

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cannonfodder
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#16: Post by cannonfodder »

I know Mark over at CG has talked about the 'universal' lack of power in 110 home machines several times. Like I said, that was my 4th grade attempt at an explanation, but Jim is the authority in process controls. Now if you want to know the 7 layers of the OSI model, that I can do.

Regardless of the reason, it is a common problem from what I discern.
Dave Stephens

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Psyd

#17: Post by Psyd »

cannonfodder wrote:Interesting. My machine is on a very low use circuit but it is at the end of the loop, about 38 feet from the breaker box, 20 amps I believe. I will have to check the power cord gauge next time I crack the case.

I believe pressure stability/adjustability will be the next target of the market. PID's have really tightened down thermal stability, but if you cannot control the pressure, your returns are limited. Some days I can pull incredible shots using my lever machine, part pressure control, part luck (Probably more luck than skill) Embarassed .




Jim would be better than I at explaining, he is the process controls master. Regardless of how much pressure your pump can generate, it requires X watts to operate at that level. If I am supplying a pump with X watts, then suddenly turn on a hair dryer in the circuit in front of the pump, that device will pull Y watts out of the circuit. So if my 500 watt pump (just grabbing a number out of the air) pumps at 9 bar at 500 watts, but I drain off 250 watts of power on that circuit, my pump now only has 250 watts to work with, so it slows down. Now my 9 bar pump can only muster 4.5 bar.
Your switch with the Isomac Millennium (The Faema isn't done yet, yeah?) at the end of 38' of twelve gauge THHN (I'm guessing, but its pretty standard for homes nowadays) on 117V (I picked the middle) is that you'd get a voltage drop of about one and a half percent. And that machine has a fifty two watt pump, and the heater is a 1400W draw. The distance is going to be a source of a *constant* voltage drop, the heater is going to be an intermittent source of a drop in the available power. Ohms law (Amps are equal to Volts times Resistance) says that the amperage is going to change with either the load or the voltage. Supposing that the voltage (for all intents and purposes) is going to remain at 117, as the resistance increases (the heater comes on line) the amps are going to drop in correlation. So, if the heater were on and the pump kicked in, you'd get a drop in the amperage going through the heater, but it would be almost unnoticed, while the heater coming on during the pump cycle shows a huge drop. Pump is 52W, heater is 1400W.

The amperage drop is going to represent a percentage of the available pumping power. If your pump is capable of 15 bar and the available power doesn't fall *below* the operating pressure of the OPV, you shouldn't notice a difference. It's when the OPV closes and the power falls below that threshold that you'll see a drop in pump pressure. Theoretically...
Espresso Sniper
One Shot, One Kill

LMWDP #175

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HB
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#18: Post by HB »

Psyd wrote:If your pump is capable of 15 bar and the available power doesn't fall *below* the operating pressure of the OPV, you shouldn't notice a difference. It's when the OPV closes and the power falls below that threshold that you'll see a drop in pump pressure. Theoretically...
The pump may be rated at 15 bars max, but its output is inversely proportional to the flow rate:

Image
Performance charts from www.ulka.it

In other words, when pulling a shot, it is operating much closer to its maximum than the no-flow rate suggests. The OPV is nothing more than a valve held closed by a spring that opens under pressure. I've not plotted it out, but I believe the amount of water it allows to escape is not directly proportional to the system pressure.
Dan Kehn

sunnyu

#19: Post by sunnyu »

another_jim wrote:I'm not sure I get you. The pressure drop on espresso pumps when the heater kicks in is quite universal; it happens to good pumps, and has nothing to do with the OPV or anything else inside the machine. The pump is electrically in parallel with the heating element, and both are in series with the wiring to the circuit breaker. The heater is 8 to 15 ohms, depending on the wattage (at 110), while the house wiring can easily amount to to 1.5 to 2 ohms if the run is long. The use of thin wires meant for 220V (4 times the resistance in the element) doesn't help either, and I urge people who have this problem to rewire the entire run from espresso machine plug to the heater with 12 gauge wire.

If the house wiring is 2 ohms (worst case) and the heater is 8 ohms (worst case -- 1500 watts), then the voltage can drop from 120 to 96 volts for the entire machine, including the pump. This will mean the pump pressure drops dramatically (about 3 bar). Mostly, it's a bit less dramatic, but drops of 5 to 10 volts, and 1/4 to 1 bar, are pretty much unavoidable depending on the state and length of your home's wiring.

You can confirm this for yourself by playing with the voltage drop calculator on Powerstream's wire size page:
http://www.powerstream.com/Wire_Size.htm
Not debating the drop in pressure, but suspect it is slightly more complicated than voltage drop, moreover solely due to wire gauge. Anyway, the numbers and logic don't add up. lets assume your worst case scenario. 120 to 96....i.e. 20% drop. and as you correctly cite 3bar drop in pump output. The user should see absolutely no difference, because the pump continuously and indiscriminately outputs 15bar that is regulated down to 10 bar. or in this case it would be 12bar that is cut down to 10.

I did not mean or want to get into a gauge measuring contest. i am merely trying to find out if there is any wear susceptible part in the pump that causes the output to diminish over time like an automobile engine!! And it sounds like all this stuff is already established and accepted. To which end, i am in your camp, why skimp on wiring.

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another_jim
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#20: Post by another_jim »

Not debating the drop in pressure, but suspect it is slightly more complicated than voltage drop, moreover solely due to wire gauge. Anyway, the numbers and logic don't add up. lets assume your worst case scenario. 120 to 96....i.e. 20% drop. and as you correctly cite 3bar drop in pump output. The user should see absolutely no difference, because the pump continuously and indiscriminately outputs 15bar that is regulated down to 10 bar. or in this case it would be 12bar that is cut down to 10.

I did not mean or want to get into a gauge measuring contest. i am merely trying to find out if there is any wear susceptible part in the pump that causes the output to diminish over time like an automobile engine!! And it sounds like all this stuff is already established and accepted. To which end, i am in your camp, why skimp on wiring.
Once again, the OPV is a simple **proportional** device, it is not a $5 mechanical PID controller. That means if the pump pressure drops, the regulated output pressure also drops. The drop is not in proportion, but damped according to the quality of the OPV (basically how much spring travel it has, the more the better). The Isomac OPV is, like all its other features, middling in this regard.

I've used a variac to pressure profile my pump in conjunction with the OPV, and it works just fine.

On the problem with your pump -- i.e. the water debit (the amount of flow in 10 seconds unobstructed) getting less. It could be the pump, but it could also be increased resistance in the pipes, for instance, a slightly jammed ball valve at the heat exchanger, grit in the gicleur, etc. etc. If you use a softener, it could be overpacked and the pump is dropping pressure by sucking harder. Finally since the pump is basically a half wave rectified solenoid bouncing against a spring, and pushing water through a plastic valve, it's quite likely to slowly lose oomph over time.

The water debit rule of thumb is that you want at least 50mL in 10 seconds or you need to clean something or fix something, as the case may be.