I would like to calculate the flow of my system, and as far as I can tell I can get this two different ways. The first is to install a flow meter on the return pipe to measure the actual flow in GPM. The other is to use a vacuum gauge on the the pump (perhaps replace the basket drain plug with the gauge), and and use the pressure pump from the filter. Then use the pump's head curve to determine the flow in GPM.
Now the flow meters tend to be a bit expensive, so I was thinking of just buying a vacuum gauge, but would like to know how accurate the results would be if I did this. I don't need to know the flow down to the last GPM, but if I could get an accuracy of about +/- 5GPM, that should work good. So how accurate would the flow rate be using the vacuum and pressure gauges along with the pumps head curve?