Perhaps worth mentioning also is that on plumbed in applications where line pressure is used, a regulator could be inexpensively installed upstream of the pump. This would allow regulation of pressure into the pump at some level just below the line pressure fluctuation. And that would keep pump pressure very constant.

Also, I just took apart a procon pump head I had sitting here. The regulator in it is spring based, not diaphragm based. What this means is that regulated outlet pressure does not vary with inlet pressure. I have no idea why we have been hearing so long that inlet and outlet are related. Based on this pump I'm staring at, it does not appear to be true.

The related inlet-outlet pressure would only apply if the working pressure was below the regulator set pressure (as might be the case if it were an emergency / safety valve). I don't think that's the case though. Don't most machines use this regulator to adjust brew pressure?

There is another regulator in there too, but it allows flow to bypass the pump, presumably to protect the pump mechanism if inlet pressure rises too high.

Sorry if that didn't shed any light on the situation.

ciao

lino

Interesting discussion Lino and Andy. In practice, I've found that the inlet pressure definitely affects the output pressure, but not 1-to-1. I assume because the spring resistance isn't linear (?). Tweaking the inlet pressure regulator is an easy way of making small brew pressure adjustments without opening the espresso machine's casing to access the rotary pump bypass.

Hmmm...

So does this mean I should consider getting an inline regulator for my new rotary pump - flojet - bottle setup? (If so does Terry sell them?)

I wouldn't bother with an inlet pressure regulator for a Flojet -- the flow rate is so slow, it's certain to keep the pressure even (spec sheet).

lino wrote:Perhaps worth mentioning also is that on plumbed in applications where line pressure is used, a regulator could be inexpensively installed upstream of the pump. This would allow regulatiion of pressure into the pump at some level just below the line pressure fluctuation. And that would keep pump pressure very constant.

My experience with several different industrial water pressure regulator valves is different than yours. The valves I've used (Watts, Bell and Gossett, etc) are generally far less accurate than you imply, IOW, they reduce downstream pressure variation but do NOT keep downstream pressure "constant." I'm told that there exist high-end versions of these valves that are more accurate, but I haven't tried them. What have you used? Have you really put gauges on them to watch the outlet pressure as the inlet pressure varies? I have, and the performance was surprisingly bad.

I need to try one of the high-end versions.

lino wrote:Also, I just took apart a procon pump head I had sitting here. The regulator in it is spring based, not diaphragm based. What this means is that regulated outlet pressure does not vary with inlet pressue. I have no idea why we have been hearing so long that inlet and outlet are related. Based on this pump I'm staring at, it does not appear to be true.

This from Procon's website:

All relief valves are preset at the factory to your specifications (60 to 250 psi range available, 30 to 250 psi range also available on certain models, consult factory for details). At the specified relief valve setting, the flow will fully by-pass from the outlet to the inlet through the relief valve chamber. The specified relief valve setting is an average; individual pumps will vary both above and below the specified setting. The relief valve actually cracks and begins to by-pass flow at approximately 50 psi below the relief valve setting. Be advised that due to the design of the relief valve, the relief valve reacts to the difference in pressure between the inlet and the outlet. As a result, the highest pressure which the pump can develop at its discharge port is the inlet pressure plus the specified relief valve setting.

I actually haven't used regulators on my water line, so I don't have any direct experience. By very constant I had assumed that the regulators would hold to one PSI or so, which I would think in espresso context would be constant enough. However certainly wouldn't be the first time I was wrong... (heh, especially in the last post!)

Regarding the the in-pump regulator...
The regulator function is:

open pressure = inlet pressure + spring force / area of valve opening
where spring force is adjustable

so (if I can try to tactfully admit a "partial" error), outlet pressure is certainly not proprtional to inlet pressure, however there is an additive component. The higher the pressure increase produced by the pump, the lower the significance of the inlet pressure.

That said, in our application, a 30 psi swing in inlet pressure would give the same swing in outlet pressure, or about 2 bar...

Way more than we'd want, by a factor of 20 or so!

Also means that what I said before was more than "partially" incorrect...


ciao

lino

lino wrote:I actually haven't used regulators on my water line, so I don't have any direct experience. By very constant I had assumed that the regulators would hold to one PSI or so, which I would think in espresso context would be constant enough.

I've had no experience with pressure regulators in espresso applications. My experience with them in general industrial applications is that the outlet pressure varies more like 10 psi than one psi. But perhaps in espresso, with the very low flow rates involved, they may do a lot better.

BTW, I went back to Schomer's book and reread all 2.5 pages of the "Pump Pressure" chapter. It's pretty vague. It appears that he keeps the little 3 gal "static" tank nearly full of water at atmospheric pressure. When he says the rotary pump will "always have incoming water at one bar, or around 15 pounds of pressure," I have previously assumed that he piped in the static tank up on the third floor, and the water running downhill produced the one bar pressure.

But now I'm thinking Schomer simply has absolute pressure and gauge pressure mixed up. Now I assume that the static tank is right under the espresso machine. By definition his pump sees one bar absolute pressure, but in practical terms this is zero bars gauge pressure. His rotary sucks its water right out of the static tank and makes the entire 8.2 bars on its own.

AFAIK, zero bars gauge pressure is OK for LM machines, but I don't know about Mistrals or Synessos. Some of you guys have undoubtedly seen his installation firsthand. Comments?

HB wrote:Interesting discussion Lino and Andy. In practice, I've found that the inlet pressure definitely affects the output pressure, but not 1-to-1. I assume because the spring resistance isn't linear (?). Tweaking the inlet pressure regulator is an easy way of making small brew pressure adjustments without opening the espresso machine's casing to access the rotary pump bypass.

I use flojet with an everpure filter feeding a rotary pump and recently decided to do away with the flojet. I found the flojet to still be a bit noisy and I wanted to see if there would be an improvement in the cup given the pressure fluctuations with the flojet.

With the flojet, group pressure bounced around 9.5-10 bars. Without the flojet brew pressure is between 8.5 and 9 without any fluctuation. I also added a check valve to the supply tube. I have never adjusted the pump pressure on this machine.

The only difference I noticed was that the crema was a bit darker. I think the taste has also improved a bit but I don't know if that is more of a product of the varying quality of my home roasts. In any event, I'm probably going to leave it as it for a while... anyone else has experience with before and after wrt the flojet pump??

The goal of the static tank is not to provide positive inlet pressure but rather to isolate the pump from vagaries in line pressure (to provide a stable inlet pressure).

Works fine with Mistrals (based on LMs) and should work fine with Synessos I think (Procon pumps etc).

I prefer an accumulator that uses a bladder to provide stable positive pressure - but I'm crazy I guess.