HB wrote:Allow me to clarify... they're called vibratory pumps for a reason:


Image courtesy of Made in the GARAGE

How much of the 60Hz back-n-forth is reflected in the gauge depends on the machine. For example, if it has a gicleur (orifice) in the grouphead, the gauge will vibrate significantly less. The sensitivity of the gauge itself also comes into play. To dampen needle flutter, manufacturers use a coil of thin copper tubing or snubber (e.g., an inline porous stone or dampening piston).

As an example, the needle on the portafilter pressure gauge I made from Ace Hardware parts vibrated like a hummingbird's wings when used on my Rancilio Silvia. It buzzed on La Valentina (E61 with gicleur), but was readable. Of course the Scace II has a quality liquid-filled gauge and its reading is rock solid.

Rotary pumps also generate pulses, but they're barely noticeable for most air gauges with no dampening.