Flowmeter Placement Questions

[BigDave]

Three quick questions:
Can I install a pitot tube type flowmeter in the straight section of pipe leading to the pump inlet?
Will it work on the suction side?
Does the inlet pipe have to be the full size of the pump inlet?

[Manslick]

I say yes to all three.

What type are you using?

Like this? http://www.keyinstruments.com/images...ucts/pr/PR.pdf

[BigDave]

Yep like that, Ben had pointed me to this http://www.bluwhite.com/Products/Var...roductpage.asp.
Thanks!

[mas985]

Keep in mind that you need 14 times the pipe diameter of straight pipe for the flow meter to remain accurate. Most pumps don't have that much pipe on the suction side. Also, on the suction side of the pump you have to deal with debris clogging the flow meter. I would recommend a pressure side install after the filter.

[BigDave]

Good point, junk in the water.
Thanks

[waste]

Keep in mind that you need 14 times the pipe diameter of straight pipe for the flow meter to remain accurate. Most pumps don't have that much pipe on the suction side. Also, on the suction side of the pump you have to deal with debris clogging the flow meter. I would recommend a pressure side install after the filter.

How would it effect the accuracy, would it read higher or lower? What would the effect be on 2" pipe if the flow meter was installed ~ 6" from a 90 or 45?

[mas985]

I haven't seen any data regarding that but the manufacture's specify the length for a reason so I would assume it is important. If the meter is too close to a fitting it could read higher or lower. Close to fittings, the pressure varies considerably in different locations of the pipe. I think the specification are set to ensure that there are no local eddies or pressure differentials. Any closer and there is no guarantee.

Venturi type flow meters are not all that accurate to begin with. They usually have an error which is 10% of the maximum reading so if your flow meter goes up to 100 GPM, that is +- 10 GPM. Unless you spend a lot of money for a paddle wheel flow meter, the accuracy is probably worse than a direct head measurement.