Unreliable Ulka pumps - Page 2

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Nate42 (original poster)
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#11: Post by Nate42 (original poster) »

Voltage at the pump is fine. I'm an electrical engineer, been there and done that. :)

dsblv
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#12: Post by dsblv »

The pump's duty cycle and pumping duration are keys to longevity. I believe these pumps can only handle a 50% duty cycle. I don't know the limit on run time, but it's probably well under a minute. These limits work okay for pulling an espresso shot. But, you can easily exceed the limits when back flushing or descaling your machine.

The Ulka pumps are used in many machines from different manufacturers and you hear of very few problems. So, if you're experiencing short life, then you're very likely exceeding the recommended pump specs. If you want to avoid worrying about pump usage, then a rotary pump is the way to go.

Nate42 (original poster)
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#13: Post by Nate42 (original poster) »

Nope, I'm not breaking the rules. In fact, as I continue to burn out more and more pumps, I have only grown increasingly anal about making sure I'm not abusing them.

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Spitz.me
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#14: Post by Spitz.me »

I had a machine with an ulka pump and since January 2010, mind you it came with a new one, I went through 3 myself. They're horrible and I'm glad I no longer have a machine with an ulka.
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erics
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#15: Post by erics »

Here is an updated drawing of the Ulka pump. I BELIEVE that the cause of the problem is a less than robust suction check valve (shown in red). This is a spherical plastic ball (the exact plastic is unknown) that has a nominal diameter of around 0.156".



Water travels through a bored passageway in the piston (shown by the dashed lines) and unseats the red ball as the piston moves rearward, filling the forward chamber with water. As the piston moves forward, the red ball seats against the piston and water gets pumped to the destination.

As the ball deteriorates (acidic descaling operation?), it can seat further into the piston and potentially "stick", resulting in zilch water delivery. With an ever poor memory, I seem to recall measuring one ball that was undersized by a few hundredths . . . enough to cause the problem. Recent measurements of used balls were all within a reasonable tolerance of 0.156".

Note that Ulka was purchased by CEME about 6 years ago. This sorta tracks with older pumps having long lives and newer ones . . . somewhat less.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com

Nate42 (original poster)
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#16: Post by Nate42 (original poster) »

Thanks guys, I was beginning to think I was nuts. I'm familiar with the ball highlighted in red, as I've disassembled these pumps before. I cleaned it with the other parts to no avail, never tried to measure it though. I would be interested to know if there is a source for the plastic balls, as it seems crazy to replace an entire pump if that's the only problem.

I've been reviewing the specs for the pumps on CEME's website. My machine came with an EAX5, which is what I've always used as a replacement. I assumed the duty cycle was 50/50, but its actually rated as 1 min on 1.5 minute off. I wonder if I'd have better luck with the EX5, which is lower power (which would actually help thermally, but might struggle with flow rate at high pressure) but is rated for 50/50 duty cycle (1 minute on 1 minute off).

danaleighton
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#17: Post by danaleighton »

Nate42 wrote:I assumed the duty cycle was 50/50, but its actually rated as 1 min on 1.5 minute off. I wonder if I'd have better luck with the EX5, which is lower power (which would actually help thermally,but might struggle with flow rate at high pressure) but is rated for 50/50 duty cycle (1 minute on 1 minute off).
Interesting. Maybe this explains why my machine's controller box shuts down the machine if the pump is running for more than a minute, which happens when I am doing a descaling.
Dana Leighton
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Nate42 (original poster)
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#18: Post by Nate42 (original poster) »

Don't know if your controller box is that smart or if its just your thermal fuse kicking in (which would be a bad thing). At any rate, I don't recommend running it for a full minute ever, as that rating assumes 25C or less water, and in reality your input water temp is almost always going to be higher than that.

Nate42 (original poster)
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#19: Post by Nate42 (original poster) »

erics wrote:
As the ball deteriorates (acidic descaling operation?), it can seat further into the piston and potentially "stick", resulting in zilch water delivery.
BTW, although I HAVE noticed some correlation between pumps failing and descaling, that wasn't the case this time. This pump started acting up before it ever got used in a descale. I went ahead and descaled my machine again AFTER it started acting up, because it was time and I figured even if it does damage the pump its already on the road to failure. I wonder if its worth the effort to hook up an old pump during descale operation? Of course if you do that the pump itself doesn't get descaled. Then again it shouldn't need it since the pump is on the cold side of the heat exchanger.

danaleighton
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#20: Post by danaleighton »

Nate42 wrote:Don't know if your controller box is that smart or if its just your thermal fuse kicking in (which would be a bad thing).
I think it has to be the controller because the heating element is disconnected during this part of the descale operation (the pump refills the boiler after being emptied). The water I use for descaling is cool water.

(edit) Oh - I see you mean a thermal fuse for the pump. I don't think mine has one. In any event, the whole circuit shuts down, including power to the rest of the machine. If I power the machine down and back up it resets the controller and will pump again. I'll make sure to wait a few minutes after the controller cuts it off before restarting to give the pump a break.
Dana Leighton
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