Thanks EricS. I now fully comprehend the difference between balanced and normal bypass valves. That being said, why wouldn't a balanced be the stock on all models?

How can you visually tell the difference just from that photo?

Thanks so much, I appreciate the description.

OP: Glad you got it working correctly! Sorry that I was less than completely helpful.

karl_a_hall wrote:How can you visually tell the difference just from that photo?

I'm not 100% sure this is right, but I think it is. Eric can correct me if need be. It's based on my experiences here, where I initially asked for a balanced bypass valve on my rotary pump, only to find that I needed a solid, standard bypass in order to perform the necessary modification (read more @ the link).

Here's a typical exterior view of a balanced bypass (from my pump):


the adjustment screw protrudes a lot more and has a locknut on it (Flickr link)

Here's a typical exterior of a standard bypass (again, from my pump after I switched):


The screw is sunk almost flush with the body of the housing, and there's no locknut (Flickr link)

That's just the exterior difference. On the inside, the standard bypass is just a (usually brass or SS) shaft with a conical area that seals against the inside of the pump between the outlet and inlet, and it forced closed by the spring, whose tension is adjusted by the screw, and the inlet water pressure. Harder they press, the higher the output pressure is in operation. A balanced bypass operates similarly, but it is a series of little plastic parts and an extra spring that are arranged in such a way to make the pump less sensitive to inlet pressure fluctuation.

Why they don't use those exclusively on espresso machines, I don't know. This Giotto is one of the first I've seen that didn't. Obviously, in a confined space the standard bypass housing takes up a bit less space, so there's that. Eric?

Well, at least I said

The rotary pump in the Giotto Professional APPEARS to be fitted with a "standard" by-pass valve.

Here is a drawing made from one on the Fluid-o-Tech website in Italy:
http://www.fluidotech.com/Pages/fluidotech_english.aspx which can only further "muddy the waters."



I surely agree with Nicholas' pics of a standard by-pass valve and a balanced by-pass valve - that's how I identified each but without an autopsy, that could be an error.