Flow meter selection help
Flow meter selection help
(OP)
I need to install a flow meter in our wastewater discharge. It is a small system and has an intermittent discharge rate of just under 10 gpm. The discharge pipe is 2" PVC.
The wastewater system treats rinse water generated in our finishing department and uses chemical flocculation to remove heavy metals in the water before discharging to the sewer. There is a very small quantity of solids (flock) in the effluent – we are allowed up to 500 ppm, but we always stay well under that, usually under 25 ppm. The few solids that do discharge usually end up sticking to the sides of the PVC piping. The piping is cleaned out monthly.
I am having a hard time finding a flow meter designed for low flow and I am not sure which type would work best for this type of effluent. I have called a few places and no one has really made me feel comfortable as to why they are suggesting the type of technology (paddle wheel, ultrasound, etc) they want me to buy. It's a lot of money so I want to make sure I pick one that will work for us.
Does anyone have any suggestions?
Thank much,
Kim
The wastewater system treats rinse water generated in our finishing department and uses chemical flocculation to remove heavy metals in the water before discharging to the sewer. There is a very small quantity of solids (flock) in the effluent – we are allowed up to 500 ppm, but we always stay well under that, usually under 25 ppm. The few solids that do discharge usually end up sticking to the sides of the PVC piping. The piping is cleaned out monthly.
I am having a hard time finding a flow meter designed for low flow and I am not sure which type would work best for this type of effluent. I have called a few places and no one has really made me feel comfortable as to why they are suggesting the type of technology (paddle wheel, ultrasound, etc) they want me to buy. It's a lot of money so I want to make sure I pick one that will work for us.
Does anyone have any suggestions?
Thank much,
Kim





RE: Flow meter selection help
RE: Flow meter selection help
If it is a pumped discharge application, your best option is a mag meter. The mag meter should be installed so that the pipe does not drain when the pump is shut off. Endress + Hauser makes a good one.
A paddle wheel is not recommended as it will foul with waste solids.
RE: Flow meter selection help
It is a gravity flow application. A diaphram pump, timed to 10 gpm, pumps the water into a large 10,000 gallon open top clarifier but from there it gravity flows out to the sewer through the 2" PVC line.
I have looked at a few ultrasonic types but so far none that I have seen will work at our low flow rate.
RE: Flow meter selection help
RE: Flow meter selection help
We have to sample our discharge monthly and send it to an outside lab to show compliance to set polluntant limits. We start an auto sampler once a month that collects a small amount of our discharge every 15 minutes for 24 hrs. The county says that using the timed proportional method is no longer acceptable (per EPA regulations) and wants us to start collecting samples using a flow proportional method. So, we need something to measure the water discharged and signal the autosampler to collect X amount of sample every X amount of water discharged.
Kim
RE: Flow meter selection help
RE: Flow meter selection help
RE: Flow meter selection help
RE: Flow meter selection help
If you have or install a basin/manhole to measure the flow at, you could install an ultrasonic level with a weir or flume or an A/V (area/velocity) meter in the pipe. Companies such as Sigma make these meters and can incorporate samplers into it as well.
RE: Flow meter selection help
I am moving on to investigate ultrasonics now.
Thanks.
RE: Flow meter selection help
The ultrasonic meters will have more or less the same issues ar the mag meters, full pipe required, etc. The ultrasonics are typically less expensive and less accurate than a mag meter.
RE: Flow meter selection help
Now you just have to measure the height of the water at the critical point. You will need to measure the water level in a 0- to 6" range.
option 1 air bubblier, reliable, low maintenance but the noisy compared to other methods
Option 2 ultra sonic level indicator, still on the noisy side in this low of a range. also low maintenance
Option 3 pressure transducer, cleaner signal than a air bubblier, the stilling well (order as part of the flume) will need to be cleaned out regularly. The pressure transducer will need to a high accuracy model. and in the low ranges you will see some drift and noise
Option 4 Vibrating wire weir monitor, with a 6" float cleanest signal that I have seen. But, again the stilling well will require maintenance and the float will need to be cleaned of the floc. I assume the monthly cleaning should be fine by hosing down the float, well and flume as the pipe is getting cleaned
Hydrae
RE: Flow meter selection help
USBR WATER MEASUREMENT MANUAL
http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/
RE: Flow meter selection help
Manholes, flumes, wiers were all suggested and would work, but I need something small as space is very limited and we also want something we can install inside, not outside the building - we didn't want to be digging up the parking lot to install flow equipment (no manholes).
Thanks everyone for your help