If a rotary pump is noisy, it is probably a vibration or your supply line/pressure is inadequate and the pump is causing cavitations. It is kind of like snorkeling and using a drinking straw to breathe through. You need a 3/8 inch line to adequately supply a rotary pump.

Sorry if I've picked up a dead thread, but I had to ask. The flow rate of rotary and vibe pumps are about the same. Why would you need 3/8" plumbing for rotary and get away with 1/4" for a vibe pump?

The VBM rotary pump is louder than I expected. However, it makes the same noise when backflushing as when brewing, so I don't think it's from cavitation. It could by vibration, as you suggest.

Gerry wrote:The flow rate of rotary and vibe pumps are about the same. Why would you need 3/8" plumbing for rotary and get away with 1/4" for a vibe pump?

They're the same during an extraction, but the unrestricted flow rates aren't the same during a boiler refill. The rotary pump will cavitate if the input is restricted.

And if the 3/8" line is particularly long or convoluted, even that might not be adequate. But it would have to be particularly long as mine is working fine and it is a good 20 feet from source to machine..

Thanks Dan and Randy. That all makes sense. I did a pressure drop vs. flow rate calc. when I put my plumbing in and decided on 1/4" for the ~10ft. run, not having your advice that 3/8 would be better. When the lever is up with no coffee, the flow is about 15 oz/min, which produces a drop in supply pressure at the regulator about 6' away from the machine of about 2 lb, from 27 to 25 lb, about what was predicted. The flow rate when the boiler fills is faster, but it seems to go smoothly even with 1/4" line. If I had it to do over, I'd probably use 3/8, but it doesn't seem worth the bother to change at this point.