Taco SR501 Zone Valve Control - Wiring..

Folks,

I have the subject zone valve controller. I have 4 zones valves all splice together and connected to this Valve Control. I've been having issues with one of the valves so I started looking into the wiring and looking at the wiring diagram, According to what I've see, this zone valve controller (501) is only made for one zone valve. Is the way it's wire an acceptable way or should I get a 4 zone valve controller?

Thanks in advance

 

Sr501- exp-4 can be expanded for 4 zones with a sr504-4. Four zones parallel into one zone?
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Taco-SR501-EXP-4-Install.pdf

 

but I have a SR501, part number 9300-822. I don't think it's and exp.

 

Couldn't find the manual with that pt number. Must be a older control. Taco makes several different type ofzone controls some have domestic hot water priority if you need it. Plus honeywell and others make controls.

 

Some TACO units are expandable. Printed on the board or lable there would EXP next to the model number.

See page 14.
https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351091630832/85170_PROD_FILE.pdf