Graco 2K Ultra-Lite 249591, Instructions-Parts List Manual

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12 309000
System Setup
Mixer Selection
Disposable mixers are available from 3/16 in. I.D. to
1/2 in. I.D. in lengths from 12 elements to 36 elements.
In general, wide viscosity or mix ratios require more
mix elements. Small I.D. mixers produce lower flow,
higher back-pressure, and waste little material. Large
I.D. mixers produce higher flow, lower back-pressure,
and fewer lead-lag ratio errors. Different mixers can
have differing “snuff-back” characteristics.
Setting the Amount of Snuff Back
The 2K-UL valve uses two “snuff back” restrictor rings
(13) to set the amount of snuff-back. These two rings
are trapped between the main valve body and the nose
piece. When the fluid valve pulls back to close, it
enters the restrictions, stops flow, and pulls the fluid
back until the needle reaches its carbide seat.
Maximum snuff-back results when both restrictors are
used. Some snuff-back is still achieved without the
restrictors because of the pull-back action of the
needles.
When dispensing wide mix ratios, it is best to use a
snuff-back restrictor only on the high volume side.
This keeps the high volume side from being pulled
back into the low volume side.
In general, use only as much snuff-back as necessary
to give a good cut-off of flow. Too much snuff-back
pulls an air bubble into the mixer. This can cause a
drip, or cause the mixer to spit when the valve is
re-opened.