Regulator "Chatter"

What is regulator "chatter"
-is excessive contact between the ball and the seat in the regulator, which is ultimately beating the seat out of the base.

This is not normal, nor is it a defect in the regulator, rather it’s a symptom of one of two conditions, either cavitation or chatter.  These are separate situations, with unique causes but with a similar end result, where the ball on the bottom of the diaphragm is striking the seat with significant frequency and force.  Technically, the only time the ball on the diaphragm touches the seat is when the pump is turned off.  It would take thousands of cycles to begin to create this level of damage.  What chatter and cavitation are and what causes this to occur can be a bit wonky/complex but we'll try to explain below:

--Cavitation is the transformation of a liquid to a vapor by way of pressure drop.  It’s not uncommon to see cavitation develop at the inlet of a pump, especially common when the fuel gets excessively warm in the tank and/or the pump is restricted on the inlet and producing abnormal levels of vacuum to get fuel.  However, cavitation is not limited to pump inlet issues and can occur anywhere in a flowing system where there’s a significant pressure drop.  This can commonly occur at a sudden/abrupt contraction/expansion point in a system, or on the trialing edge of a sharp/hard 90 degree transition.  The cavitation event can entrain bubbles in the flowing liquid which, when they attempt to pass between the ball and the seat in the regulator (the point where pressure is created and maintained by the ball and seat) the bubbles either split or collapse.  When this occurs the spring drives the ball toward the seat in the void, and if the bubbles are frequent/large enough the ball on the diaphragm will strike the seat, and if sustained will eventually damage the seat.

--Chatter is a condition where the fuel pump / flow volume is insufficient to keep the ball from touching the seat under full load (the regulator is attempting to prevent the pressure from dropping by closing the return path, which is the area between the ball and the seat).  On the test stand this can be easily demonstrated by flowing through the regulator to a flow meter with a ball valve used to simulate engine fuel consumption.  Typically the ball valve starts closed and all the fuel is running from the pump through the bypass and back into the test tank reservoir to start, then the ball valve to the flow meter is gradually opened to simulate increasing engine fuel consumption.  As this occurs the regulator adapts by closing the return (moving the ball closer to the seat) to maintain pressure.  However, as the flow rate of the pump becomes insufficient to feed the increasing opening of the valve to the meter the pressure will droop 3-5 PSI and then the ball will start to contact the seat in an effort to keep the pressure from dropping further.  At this point the ball will touch and the restriction will be complete, allowing the pressure to come back up, but as soon as that occurs and pushes the ball off the seat the curtain area at the smallest lift flows more fuel than remains and the ball is forced back onto the seat.  At this point on the test stand an audible chatter can be heard as the ball rapidly and repeatedly strikes the seat and, if allowed to continue, will progressively damage the regulator seat.