Standpipes and Gated Wyes

Today, we conducted a brief experiment to determine the pressure loss in a 2 1/2" x 1 1/2" gated wye when the use of 2 1/2" hose is desired. A 20' section of 2 1/2" hose was attached to the flow tube on the fire hydrant. We used adapters in place of a bushing on the outlet of the wye with the following results;

With gated wye. 1 1/8" tip, 250 GPM. The flow was verified with a flow meter and handheld pitot gauge. Pressure at hydrant was 83 PSI. Tip pressure 50 PSI. Pressure loss was 33 PSI

Without gated wye. Same tip, same flow. Pressure at hydrant was between 48 and 50 PSI with corresponding tip pressure readings, meaning the pressure loss was negligible without the wye.

Assume a loss of 25 to 30 PSI through the valve with a setup like this. As you can see, the old 10 PSI loss is a big underestimate here.