Pump is acting weird - how to test for steady pressure? - Page 2

by **LeoZ** on Fri Mar 16, 2007 9:25 am

cannonfodder wrote:Yup, that is the little monster. You can get uber precise certified gauges but they are very expensive and just not necessary for your application. I have made a couple of these as well as installing an on-board pressure gauge. While there is a slight discrepancy between gauges they are always within .1 bar of each other. That should be more than sufficient to tell you if your pump is going wacky. If you 8-9 bar you are ok, if it goes from 0 to 8 to 6 to 9.... Then you know you have a problem.

On a side note, if you are concerned about the pump suddenly going out, just purchase a spare. Vibe pumps are not very expensive and easy to replace, two wires, two hoses and you are finished.

i agree, i may just snag one..

im thinking about an onboard gauge as well, though, with it being so difficult to adjust the opv, the benefits of a gauge to easily watch adjustments may be outlived. :/

i thought you could connect the gauge to the 'dry' part of the line, and get just as accurate results? courtesy of dan, of course:

from http://www.home-barista.com/forum...sure-t153.html#889

this line doesnt have water in it, correct? at least ive never seen water in it, unless its the OPV line, which only sees water at max pressure?

by **LeoZ** on Fri Mar 16, 2007 9:30 am

erics wrote:Leo -

The gage you are holding in your hand looks like an automotive compression tester gage - perhaps it has seen a few bumps in its life

Here's a freebie you can do:

Measure the flowrate in the OPV line going back to the tank with a blind filter in place. Measure the amount of time it takes for, say, 4 ounces to flow into a Pyrex measuring cup and convert this to cc/minute. The best way to do this is to fill the cup with a couple of ounces to begin with and then simply measure the time it takes to go from the 4 ounce mark to the 8 ounce mark. Certainly a Pyrex cup is not "lab accuracy" but the delta may not be too far off the mark.

Use this formula to determine pressure in bars:

P = (-.02333)(cc/min) + 15

This is just a simple equation derived from this:

<image>

This should very closely approximate what a gage would read with zero flow from the PF. True brew pressure is about 0.2 to 0.3 bar less than what is calculated or measured with a typical E-61 group. Obviously, the better method would be to use an accurate, liquid-filled gage and a needle valve arrangement to measure the pressure at YOUR chosen flowrate as discussed in this HB resource topic:

http://www.home-barista.com/forum...-machine-t420.html

thx for the chart, interesting. so, you actually get less flow with higher pressures from this pump? i havent opened it up yet, again, but just took another 'air compressor gauge' (yes, it was bought new!) reading, and im getting 8.5bar during a backflush, and, when the heating element kicks in, its shoots up to a little over 9 bar. i may actually lower it to 8.25 or so, just to keep theoretical max at around 8.5. i guess the pump is holding out, just being quiet. guess i dont mind!

if i have time after working today ill open it and try your opv measurement..

btw, meant to ask, the pic on your site, HX04, is interesting. can you explain it? i dont understand why the bottom line (return/opv?) from the e61 goes back to the HX loop. can you explain, or should i start a new thread?

by **cannonfodder** on Fri Mar 16, 2007 9:09 pm

I had to dig back in the archives to find my old modification thread. Here is what I did to my Isomac Brew Pressure, Boiler Insulate, Preheat HX coil for Isomac

by **LeoZ** on Fri Mar 16, 2007 9:15 pm

cannonfodder wrote:I had to dig back in the archives to find my old modification thread. Here is what I did to my Isomac Brew Pressure, Boiler Insulate, Preheat HX coil for Isomac

i saw that post, and thats why i questioned the best place for a gauge, before or after the HX line..
you put yours before the group, the pic i posted appears to show it after.

by **cannonfodder** on Fri Mar 16, 2007 9:44 pm

I don't know how you could put a gauge on the hot side of an E61 style HX machine. You would have to chop into your thermosyphon line to mount one there.

I removed the HX input line, added a bit of copper, put on the T for the gauge and ran the HX input line down the side of the boiler, looped it under, back to the top and down the top keeping it nice and tight against the boiler. Then it goes into a 90 degree elbow and straight down into the boiler HX input. Then I over wrapped the works with some ceramic insulation.

If you add a gauge, or even make a portafilter mounted gauge, check the temperature spec on the gauge and make sure it is rated for the high water temperature or radiant heat inside the case.


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