Posted Tue Jan 21, 2014, 12:09pm Subject: Systematic approach to Low Pressure Low Flow, ULKA Pump Problems and Diagnosis
Several threads have asked about ULKA and other vibe pump problems, and diagnosis on multiple types and brands of machines. The conversations then seem to center around how to separate pump problems from machine outflow obstruction problems. Opinions vary and there does not seem to a clear path to separate the problems. Pumps are relatively inexpensive and fairly easy to change so that is often advised. Descale is reasonable, if is was not already not the preceding event, even then more descale may be needed. Open cleaning of the machine is at times advised. Of course the best thing to do is to fix the actual problem with the most cost effective and least labor intensive appropriate approach. A current thread illustrates that difficulty.
prove a good pump or find a bad one? Bad output suggests a bad pump, or at least one in need of service.
A baseline flow is 165 - 175 ml in 15 seconds by running the pump on a 2 year old Gaggia Classic through the brew group combined with outflow from an open steam wand. About 2/3 of that flow was from the wand and about 1/3 from the group. That is 660 - 700 cc/min or normal baseline for about 0 pressure. Does it help to have a baseline on your equipment? With a known baseline and now tested low output , and a “water debit test” back at baseline flow, then it might suggest obstruction in the machine.
In addition, if flow is only from the steam wand the output is about 155- 160 ml/15 seconds and if the brew group only, about 145 – 150 ml/15 seconds.
This is not a Gaggia specific thread and it seems that the information might help on any given brand and make of machine to know those rates. Normal wand flow but poor group or brew output seems to suggest that the pump works but the group is occluded or puck too tight. Of course that assumes normal flow at low pressure reflects a healthy pump. How far off of the given baseline flow rate suggests a pump problem?
If OPV outflow is also collected all output is accounted. Of course an unobstructed system should not backflow through a normal OPV.
Does it make any sense to measure pressure at the group, or if no gauge, measure OPV output against a blind basket at the group, and then compare to the flow versus pressure chart?
If low flow, low pressure or low output the pump may be suspected, but not the culprit. The problem can be approached by best experienced guess or somewhat more systematically. If the machine is primed and water will flow with the wand and group open, that seems a good place to start.
Flow can be measured with and open group, preferably with the screen off, and an open wand. If the machine output pathways are clean of scale coffee debris, the expected outflow from a good pump would be about 650 - 700 ml/minute. That is easily calculated with a 15, 20, or 30 second run. A couple runs should be done and averaged. If that flow rate is not normal, then the pump may be bad, or the outflow pathway not clear. A WDT as described above should differentiate pump versus outflow problems. WDT is not necessary if the flow is normal. Differential flow can be done with just the wand or just the group to see that they are individually clear.
If the pump is at low flow, it may improve with cleaning as noted.
The OPV can stick in the closed position and cause problems with high pressure and could harm the pump as there would not be pressure relief.
Not documented so far is normal low pressure flow and a bad pump.
Posted Sat Feb 8, 2014, 3:20pm Subject: Re: Systematic approach to Low Pressure Low Flow, ULKA Pump Problem/ Diagnosis
Also, it should be noted that normal function of the 3 way can easily be documented. Adequate drip tray discharge and blockage of the group with use of steam switch and brew switch and high flow through the wand.
Quick and simple tests for pump pressure and flow problems.
For Gaggia with 3 way and OPV a few minutes of non-invasive, non disassembly testing will help.
With a primed pump and full boiler measure flow from the group and wand together.
Measure flow through the group, and then flow through the wand only. Wand only is brew switch + steam switch with an open wand. Note that this is 3 way dependent.
If all normal, then the pump is working and the 3 way, and the outflow passages.
Finally the OPV should be tested with an occluded group and separate "tank" and collection containers.
Those quick and simple tests should help make a systematic approach to what is needed to improve flow before any disassembly needed.
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