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Flow Transmitter for Cooling Water
Proper Flow transmitter for Cooling water

What is the best choice for measuring flow in 36" cooling water pipe?
Also, I have another question about what is the best choice for flow measuring of high viscosity fluids (600 cST)?

By Bob Peterson on 7 June, 2017 - 10:31 am

"Best" is a very subjective term. I think you would need to define what you mean by the term before anyone can give you any serious advice.

There are all kinds of technologies that would probably work adequately.

Pricing is all over the place from relatively inexpensive paddle wheel or turbine type sensors to very expensive technologies.

What level of accuracy you require may also have an effect on the choice, as could the range of flow velocities that will be encountered.


The best choice for cooling water would be a magnetic flow meter. However in 36" it would be expensive. We usually use a pitot tube and DP transmitter for that reason. You want to avoid DP instruments like orifice plate because the losses are so great.

Propeller type flow meters can be purchased quite cheaply with weld on saddles for large lines, they measure the line velocity which you can then calculate Velocity x Cross Sectional Area to work out flow.

I don't have much experience with high Viscosity liquids but I would avoid anything mechanical like a turbine. If it's conductive a Magnetic flow meter would be a safe choice. Time of Flight Ultrasonic should work.

I had to back out to see what corresponded to 600 cST. it seems to fit somewhere between 30 and 40 weight motor oil, some sort of positive displacement meter perhaps, Not a turbine.

If it's just a rough reading you need an orifice and DP cell will give quite good results and surprisingly not effected too much by temperature. I used to do a lot with Mill lubrication systems supplied by a gear pumps the DP cell worked better than anything else I could find.

Hope this helps

In my previous project, we use Pitot Tube Flow Element with DP Transmitter for 56 Inch Cooling water line and so far is good.

I do not have much experience about high viscosity flow measurement, but based on Liptak book that I have read, you can use Coriolis & PD Meter.

we can not suggest you about what is the best choice because is depend on yours.
Best about accuracy, price, delivery time etc.


Thank You all for your replies.

Generally in this plant, orifice is used. But at these two services because of the size of the line for cooling water (36"), and the viscosity for the vacuum residue, I think about other solutions, and of course the price is important.

Does anybody know the limitation of viscosity for orifice plates? Also, what do you think about wedge type DP meter for high viscose service?
About cooling water, what about ultrasonic? how much does it cost for this service to use ultrasonic instead of annubar (pitot)?

Time of flight ultrasonic should work well if you have a good spot to install it, lots of straight run.

I wouldn't even consider Doppler ultrasonic.

By John Catch on 9 June, 2017 - 1:56 pm

There are a number of high quality insertion turbine flow meters (not paddle wheel type) that would do an excellent job on this application. Vendors such as Vortek, Spirax-Sarco, Hoffer, Flow Technology, and InFLOW, INC. all have products that will give years of service, generally with virtually no maintenance and performance is field verifiable.

Although "no moving parts" meters may sound attractive, in actuality all meter types have their weak points. Also, insertion turbine meters typically are the most cost effective in this type of application.

For high viscous fluids positive displacement meters are very attractive. However, there are special orifice designs that can be used for high viscous or low Reynolds number applications. So if you are comfortable with DP measurement this may be an attractive option, especially if the flow rate turn down is not too great.

John Catch