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Autotrol 155 or 255 - Injector Size / Color - Why BLUE is sometimes used on 8 inch tanks
Last Updated: 01/28/2019
Often you will find a Blue Injector ( AP28F-BB, 1032971 ) installed in an Autotrol Valve used on an 8 inch diameter tank,

Most valves come from manufacturer with the BLUE injector installed ( since most common residential tanks are 9" or 10" diameter ).

And it's not "necessary" to down size ( White Injector has smaller internal holes for reduced flow rate ).
The slightly large internal ports ( holes ) of the BLUE injector will allow better / more water flow through the Valve and Tank.
And less likely to "clog" internally.

And this is beneficial when the Valve is used on well water that has lower pressure ( like 20 - 40 psi, or even 30 - 50 psi ).
It just makes sense to use the next size up, for better flow rate during the 50 minute Brine Rinse ( suction and rinse ) Cycle.
You don't want to leave any of the Salty Water in the Resin tank. You want it completely rinsed through and out of the tank.
That is the main reason for different Injector Size / Colors.
The larger the tank ( diameter ) the more FLOW is required to properly suck in the Salt / Brine water, and Rinse if all out, in the normal 50 minute cycle time.

It's been common practice in South Florida to do this on Well Water ( use BLUE instead of WHITE ), as the common above ground shallow well jet pumps often only reaches 40 or 50 psi.

But since you only "need" the White Injector, when pressure is good ( 50+ psi ), and all "city" water, and most submersible pumps provide this,
We install the Injector size / color as specified by the manufacturer in all Autotrol 155 ( replacements ), which is the 255.
When you order the APK5 or AP24NC.
And also, the Newer "logix" controlled versions, use matching sized injectors based on
tank diameter too.

Model 155...........................................................................................Model 255

How do I know if I have an Autotrol 155 ( 1550-TC ) or a model 255 Valve?

The Series 155 was replaced by the Series 255 late 1995 ( early 1996 ).
An easy way to tell the difference is, the brine control ( salt dial ) is located on the front ( just beneath the timer housing ) on the 155 and it has been relocated to the right side ( looking from the front ) on the 255.

Another noticeable difference is the Injector Cap, and Injector Screen/Cap are the size of a quarter on the newer 255. They are about the size of a dime on the older model 155.

Note: The Brine Control and the Backwash Flow Control plugs are identical in size on both the 155 and the 255. However, another difference is the location of the Backwash Flow Control Plug ( 25F )is on the right hand side ( looking from the front ) on the 155 and has been moved to the left side on the 255.

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