Flojet and rotary pump questions - Page 2

[DavidMLewis]

1. Would you mind briefly explaining how the Flojet pump system works? I've never used one of them. My reason for asking is, of course, if the inlet pressure to the rotary pump varies, the outlet pressure will vary by the same amount. I'm just wondering if pressure control is poorer with this setup as compared to a typical plumbed in commercial machine.

Hi Andy,

Machines vary in this. Some, like the Astras, have an onboard pre-regulator. And some rotary pumps, like the Fluid-O-Tech Compact series and I think a number of others if ordered this way, have a balanced pressure relief valve that doesn't vary its output pressure as the input changes. Either one could have been used in this case, for all I know.

Best,
David

[AndyS]

...some rotary pumps, like the Fluid-O-Tech Compact series and I think a number of others if ordered this way, have a balanced pressure relief valve that doesn't vary its output pressure as the input changes.

I'm from Missouri (figuratively, at least). Can you provide the reference for this? Looking at a diagram of a Fluid-O-Tech Compact pump, it sure looks like the regular old dumb bypass valve.

[DavidMLewis]

...some rotary pumps, like the Fluid-O-Tech Compact series and I think a number of others if ordered this way, have a balanced pressure relief valve that doesn't vary its output pressure as the input changes.

I'm from Missouri (figuratively, at least). Can you provide the reference for this? Looking at a diagram of a Fluid-O-Tech Compact pump, it sure looks like the regular old dumb bypass valve.

I suppose there are a lot of soybeans in Missouri. If you look at this page, which describes the current ones, at <http://www.fluidotech.it/public/Download/brass.pdf>, you'll see the following text:

The pump is equipped with a built-in by-pass;
a special balanced by-pass (able to maintain
the set pressure for variations of the inlet
pressure) is available upon request.

That's what I was referring to. The older Compact series had it by default, I believe. How good a job it does of maintaining regulation in the face of input pressure variations, I have no idea.

Actually, if you look at <http://www.depcopump.com/datasheets/Fluid-o-Tech/compact%20rotary.pdf>, which is the description of the line as a whole, it says:

The pump is equipped with a built-in
balanced by-pass able to maintain the set
pressure for variations of the inlet pressure.

I'm just the messenger, as I said. If you look at the parts sheet for the brass series, which is available both ways, at <http://www.depcopump.com/datasheets/Fluid-o-Tech/brasss%20rotary%20parts.pdf>, you can see the differences. I've never taken a pump apart, but I suspect you have many times, so maybe this will tell you something.

Best,
David

[AndyS]

If you look at this page, which describes the current ones, at <http://www.fluidotech.it/public/Download/brass.pdf>, you'll see the following text:

The pump is equipped with a built-in by-pass;
a special balanced by-pass (able to maintain
the set pressure for variations of the inlet
pressure) is available upon request.

That's what I was referring to. The older Compact series had it by default, I believe. How good a job it does of maintaining regulation in the face of input pressure variations, I have no idea.

Actually, if you look at <http://www.depcopump.com/datasheets/Fluid-o-Tech/compact%20rotary.pdf>, which is the description of the line as a whole, it says:

The pump is equipped with a built-in
balanced by-pass able to maintain the set
pressure for variations of the inlet pressure.

I'm just the messenger, as I said. If you look at the parts sheet for the brass series, which is available both ways, at <http://www.depcopump.com/datasheets/Fluid-o-Tech/brasss%20rotary%20parts.pdf>, you can see the differences. I've never taken a pump apart, but I suspect you have many times, so maybe this will tell you something.

David, thanks for the links. I was unaware of this stuff from FoT. I'm skeptical of their claim, because I've tried too many other pressure reguation devices that didn't live up to their hype. But I'll try to get one of these balanced bypass doohickeys to try out.

[wildlyesoteric]

great thread; worth resurrecting

I'll use it for my own selfish means -- after what I've read, am I wrong in thinking that I could run a commercial machine like a Nuova Simonelli MAC2000 or Rancilio S series straight into a bottle? I'm about to bid on a flojet dispenser.

[erics]

Yes, as long as you keep the size of the inlet line to the pump equivalent to the 3/8" BSPP suction port on the pump. In any event, some machines NEED to sense a positive pressure before they become operational - some Cimbali's come to mind and there may be others.

IMO, the very best way to supply a rotary pump is with a static tank within a foot or two (elevation wise) and not more than, say, three feet from the machine.

I would certainly think you could get by w/o a flojet if you follow the installation guidelines from the particular pump manufacturer.