Selecting the Right Flowmeter?

[Hansen66]

Hi there
I need to find a precise flowmeter for a hydraulic system. The flow meter should meet the follwing:

1) The flow i need to measure is between 0.3 and 40 gpm

2) the accuracy should be aronund 0.3%

3)As the flow is measured continuous it has to pick up changes in flow rather fast

4)The pressure drop across the flow meter should be as small as possible (preferably under 14psi at 40 gpm)

The flow is measured on the returnline so the max working pressure does not have to be large. Im using an oil with a viscosity around 46 cSt and the temperature is around 100 F. I know this can be done with either magnetic flow meters or ultrasound but these seem to be very expensive so Im hoping you guys might know a better alternative

Best regards and thanks
Hans

 

[hydtools]

Have you looked at Webster flow meters?

http://www.webster-inst.com/

Ted

 

[IceStationZebra]

The only cheaper alternative would be a high end turbine flow meter with linearized output. I would get it calibrated with your intended straightening tubes to keep the accuracy.

http://www.ftimeter.com

ft series

You might also check out vortex shedding, but I have no experience with them.

ISZ

 

[micalbrch]

What is the pressure in your system (the pressure the flow meter will see)?

 

[Hansen66]

As the flow meter is placed on the return line hopefully it won't experience more than 0-70 psi

 

[micalbrch]

http://www.parker.com

They have flowmeters for hydraulic circuits and have a worldwide presence.

 

[faqs]

Your requirements are very stringent. I don't know if they can be met. Look closely at the turn down raio. The only meters I know of that will do a 100:1 are positive displacement.

These are 2 that we use.

http://www.maxmachinery.com/top.html

http://www.vse-flow.com/english/flow-counter.php

Another is:

http://www.aw-lake.com/

 

[ccfowler]

The combination of accuracy requirement and turn-down ratio are really very extreme. What is your accuracy standard? If by .3% you are refering to that level of accuracy at 40 gpm, the allowable error would be +/- 0.12 gpm at any flow.

I can't imagine any reasonable alternative to positive displacement flow meters for a turn-down ratio of 133 to 1. In order to maximize the accuracy of the flowmeter, you will need to minimize the pressure differential that the flowmeter will experience, so it would be best to locate it very near the reservoir with generously sized piping. Positive displacement flowmeters will usually provide very good response to flow rate changes, but even they will suffer brief deterioration in accuracy for very abrupt changes in the flow rate.

If this is being used for some sort of control function, and you are relying on this return flow being measured with such great accuracy, what about the effects of leakage within your system adversely affecting the value of the return flow for the control function?

You know what you are trying to do with your system, but such high levels of accuracy for metering in a hydraulic system seems a bit odd to me. Is it possible that measuring some other parameter(s) in your system could serve your needs better and more economically? Very high accuracy flowmeters need to be treated very carefully to maintain their accuracy. Avoiding impressed vibrations may be a serious problem depending on your application.

If what you actually need is excellent repeatability, rather than accuracy, you may want to consider using an excellent quality haydraulic motor rather than a positive displacement flowmeter. It could be installed anywhere in your circuit that would make sense for your purposes, but it would be operated without load, probably only having a toothed steel wheel on its output shaft to provide a signal for an electromagnetic sensor. I would probably prefer using a "Gerotor" type of motor for its relatively gentle internal flow patterns to assure the most consistent flow rate vs. shaft speed characteristics.

If you could provide more information about your system, that would make it possible for others to provide better assistance to you.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.