Hello. I am new to Survey 123. I would like to create a survey using the Collector app and Survey 123 for testing fire hydrant flows. I would like to use Collector to select the hydrant, have it open Survey 123 so the inspector can add some information about the hydrant and the flow data (Static, Residual, and Pitot flow data) and then have the capacity calculated automatically by Survey 123. This seems achievable but I am struggling getting the formulas to calculate the capacity and I fear it is something simple in the calculation that I am missing.

### HydGPM: Theoretical Discharge through Circular Orifices Formula

Computes a flow-rate in GPM given a psi and coefficient of the flow device.

**Q = 29.84 x √P x D² x C or 29.84 x [(√Pitot) x (Diameter²) x (Coefficient)]**

Q = flow-rate in GPM (Field = HydGRPM)

P = velocity pressure in psi (**Pitot** - measured at the hydrant in the field)

D = orifice diameter in inches (**Diameter** = 2.5 inches)

C = coefficient of flow device (**Coefficient** = 0.9)

### HydGPM_20: Equation for Determining Rated Capacity

Computes the flow-rate available at a specified residual

pressure (a.k.a. Rated Capacity). The example below enables

you to find the predicted flow-rate at 0 psi residual pressure.

Use this when fire flow testing hydrants.

**QR(20) = QF x (HR ^{0.54}**

**/ HF**

^{0.54}) or QF x [(Static -20)^{0.54}**/ (Static - Residual)**]

^{0.54}QR(20) = Flow-rate predicted at the desired residual pressure in GPM

QF(20) = Total test flow-rate measured during test in GPM (QF =

**HydGPM**calculated)

HR = Pressure drop from static pressure to desired residual pressure (

**Static**– 20 psi) (

**Static**measured in the field)

HF = Actual pressure drop measured during the test(

**Static**– Actual

**Residual**) (

**Static**and

**Residual**measured in the field)

I realize this is a big ask but I would truly appreciate any help with this. I have attached several screen shots.

Thanks

Doug Wenning

Hi Doug,

Taking a quick look at your screenshots, I notice the first line in ScreenCap2 is missing a set of brackets for the sqrt.

It should be sqrt(${Pitot})

You have the opening bracket before the sqrt text not after. See example here: New Mathematical Functions Make your Form Smarter

Once the brackets are fixed up, try and validate your survey again. Missing brackets or brackets in the wrong place in calculations will cause validation and pyxform errors that don't make sense or point directly to the problem in survey.

Phil.