Happy thanksgiving to all.

Using a Scace 2, I'm wondering if there is more to measuring the pressure than locking it in to a clean machine, running the pump and reading the gauge? If anyone with experience using this tool could confirm or advise, I'd appreciate it as I can't seem to find any instructions for the version 2 and would like to ensure I'm not using it incorrectly.

When adjusting my machine's OPV valve, I can dial the brew pressure up to a reading of 110psi on the Scace 2. At this position, the machine's built in pressure gauge against a BF disk reads ~10.5 bar. The part that I'm confused about is that further adjustments to the OPV valve don't get me any > than 110 psi on the Scace 2 but, against the BF disk the machine's gauge continues to increase in pressure. With the OPV valve 1/4 turn from full pressure, I still get ~110 on the Scace 2 and ~14bar against the BF disk. I don't see anything leaking around the PF gasket with the Scace in place.

Am I doing something wrong or could this indicate a problem with my machine? (New pump, OPV and deaerator installed today)

Any suggestions or advice appreciated.

Thanks.


UPDATE 12/11/10: Summary with resolution.

Scace 2 pressure gauge instructions confirmed: Clean machine, load Scace 2, run pump, read gauge.
Pressure problems / quiet pump / surging pump: Resolved with new vibe pump.

Thanks to everyone for their help!

As a general rule, espresso machine gauges are junk. Trust the Scace. You are also measuring pressure with flow and with no flow when using a blind basket. The blind basket will read higher. The location of the capillary tube in the hydraulic system will make a difference as well. But all that said, in Scace we trust.

Tom_MN wrote:The part that I'm confused about is that further adjustments to the OPV valve don't get me any > than 110 psi on the Scace 2 but, against the BF disk the machine's gauge continues to increase in pressure. With the OPV valve 1/4 turn from full pressure, I still get ~110 on the Scace 2 and ~14bar against the BF disk.

This is normal. For a vibratory pump, the effective pressure is inversely proportional to the flow rate. More flow means less pressure. Against a blind filter basket, there's no flow, so you're measuring the pump's maximum pressure less the pressure reduction due to water escaping from the OPV. Using the Scace II, you're measuring the effective brew pressure under normal espresso flow rates, i.e., the pump's maximum pressure less the pressure reduction due to water escaping the thermofilter and possibly the OPV. The thread I still don't get it: Why adjust the OPV? and others linked from it elaborate on this point.

For the sake of completeness, Scace Thermofilter Temperature Device - Instructions covers the Scace I instructions and WBC Procedure for Measurement of Brewing Water Temperature documents the standard SCAA calibration procedure for commercial equipment.

Thank you all for the responses and links.

erics wrote:Operate the machine with the Thermofilter II in place and adjust the OPV until the machine's gage reads 9.0 bar. At this point, what does the gage on the Thermofilter II read and, if you can, provide a value for the flow from the device - ounces/minute or ml/minute.

This produces ~2oz in 25s while displaying a little less than 100psi. Thanks for the link to your post for cleaning the group. I cleaned out the upper part of my group using your post as a guide; thankfully, after ~3 years, I found very little evidence of scale or an obvious obstruction. And you're right, the machine's pressure gauge looks to be connected at the top of the brew boiler.

HB wrote:This is normal. For a vibratory pump, the effective pressure is inversely proportional to the flow rate.

OK, thanks. Ultimately I've left the OPV set to where the machine's gauge reads a touch over 9 while pulling a shot. This is about 10.5-11 against the BF disk.

cannonfodder wrote:As a general rule, espresso machine gauges are junk. Trust the Scace.

Agreed. This tool was incredibly helpful in providing water temp info to adjust the offset (installed a Gicar PID with the new pump). I'm still not quite sure I understand why my machine can't seem to produce 9 bar on the Scace; seems like it should be able to if the machine was working correctly. However, I believe I've dialed it in the best I can for it's current condition and its making good tasting coffee so I'll leave it as is for now and see how it goes.

Thanks again to everyone who contributes to this site; what a terrific source of information it is!

Hi tom:

email me at gscace@comcast.net with questions or phone at 240 252 zero two four two and I can pretty much answer everything Scace related.

-Greg

erics wrote:That aspect is good but I do believe you still have an uncovered problem.

I think so too. I paid careful attention to the four holes you mentioned, in addition to a smaller hole in the center of the part (the one covered by the screen) - all of them are very clean. I also took down the shower screen and removed and cleaned the hole in the brass screw in the group head.

I've actually ordered another pump and OPV as I'm suspecting I might have damaged the one I just installed by not respecting it's duty cycle after installation (re-filling the boilers, testing pressure etc). The more I've used it the last couple days, the more I can tell something is wrong. Mid shot, the noise from the pump goes very quiet and the pressure drops several bar on the pressure gauge, after a few seconds it gets louder again and regains pressure. This "surging" happens on every shot now. The reason I replaced the pump to begin with was that it was taking it 25 to 35 seconds to build pressure, which the new pump corrected, but this surging is new and doesn't seem like it can be normal.

Thanks for your continued feedback. If there is anything else I can check while I'm waiting for the parts... I'm getting pretty good at opening the machine )

erics wrote:That exact problem has been previously reported and the "solution" was a pump replacement, IIRC.

Thanks Erics, I'll post the results after re-replacement of the pump/OPV. Needless to say, I'll be more careful with it this time.