I built a proportioner for my soft wash system. I tested the ball valve on the water side to see if the draw is the same as the metering valve.

Updated 5/4/2024: Parts list for all fittings from Farmchem.com. Farmchem does not have the check valves so you need to get them from US plastics.com or another source. Just remember to make sure they are 1/3 crack pressure. You will need to purchase the metering valves separately. I went to my local pool company to purchase Pentair valves. I upgraded to the 1/2" Asahi valves from the Pentairs. You could also convert all the fittings to 3/4" for additional flow if needed.

3 HB050 (1/2" MNPT X 1/2" Hose Barb)
1HB050025 (1/2" MNPT x 1/4" Hose Barb)
1 CR050 (1/2" 4way)
6 NIP050SH (1/2" x 1.75" Nipple)
3 HB05090 You can use this 90 or a straight fitting depending on your set up (1/2" MNPT x 1/2" 90 degree Hose barb)
3 22210 (1/2" Check Valves from US Platics.com)
2 SL05090 (1/2" Pipe Elbow)
1 HB050075 (I chose to use this fitting from the proportioner to the pump. (1/2" MPNT x 3/4" Barb)