Accurate Volume Flow measure 1

[gt6racer2]

Can anyone advise on best way to accurately measure the volume of fluid passing down a pipe ?
Particulars :
Fluid : Mineral Oil - Viscosity 10 cSt at 40C.
Volume to measure 4 L, accuracy to 1cc
Flow Rate 10 L/min
Pump Pressure 1000PSI
Fluid will be solid - no foam.

 

[jmw]

Most usually positive displacement meters are used for oil flow measurement though in some applications mass flow meters are used.

However, you seem to suggest a batching or dosing operation as you wish to dispense 4 litres in 24seconds.
An accuracy of 1cc seems rather ambitious i.e. 1 part in 4000 and you not only have to contend with meter accuracy but control accuracy as well. You not only need an exceptional meter but a very fast acting and very accurate and repeatable shutoff valve even if using multistage shutdown, which hardly seems practical in a 24second duration batch.
This will take exceptional control using a flowmeter and a shutoff valve/pump stop due to cycle times and the repeatability of the valve and meter. 1cc seems an ambitious target at this flow rate.
Also you will need to include temperature and viscosity corrections for a PD meter to get anywhere close and for a mass meter you will need very good density measurement to get back to volume flow.
I am not sure what accuracy you would get using a metering pump but you may find this will provide a solution.

Might be best to use a calibrated piston displacer i.e. a piston with a precisely calibrated volume of 4litres per stroke.

JMW

http://www.ViscoAnalyser.com

 

[unclesyd]

I have to concur with jmw that a metering pump is the way to go. With you require accuracy it is going to take a very precise metering pump to achieve this kind of accuracy. You will have to have a precision speed control on the pump.
This is a very high flow for a lot of these pumps. I would suggest that you contact the following companies and discuss your requirements.

The highest capacity precision syringe/plunger type pump is 1L and even in tandem I believe the flow rate is too high.

We have both companies pumps in routine service.

http://www.zenithpumps.com/product.htm

http://www.mmscusa.com/products/precisionpumps.asp

 

[gt6racer2]

Thanks for the input. I should have added that this isn't really a control issue. I'm filling a known volume and the measure is to check that the volume went in.

Some more detail.
I have a closed hydraulic system which is to be filled by evacuating to 5 Torr and then pumping in fluid. ( Which has also been evacuated to remove air ). The measure is to confirm that the fill process worked.

 

[StoneCold]

You might want to look at an ISCO syringe pump. They work just like a giant syringe so you would be sure that all your fuid went in. Just a thought that you might have better results if you could slow down a bit.

Regards
StoneCold

 

[gt6racer2]

The comments are in line with my thoughts. Long term I will use a two stage cylinder delivery - a large one to quickly pump just less than 4L and then a small one where I can accurately measure the volume from the piston position. Unfortunately, my need is urgent and I have to get something off the shelf to measure my existing set-up (pressure controlled servo pump) output. I've done more research, but still not found a positive displacement meter better than 0.5%.
I can slow down the fill rate, but the meter's I have found all state accuracy as percent of volume delivered - so the accuracy is not affected by flow rate.
Thanks for your input..

 

[jmw]

My appologies for my original garbled reply, it must have been a late night coffee fuelled posting.

The most accurate PD meters are usually the Avery Hardol (part of Cobham Engineering or Flight refueling) or possibly the Tokheim, Gilbarco etc multi-piston meters used for petrol/gasolene forecourt metering.

You will get PD meters suitable for better than 0.5% but you are going to pay for them and I couldn't say if you are going to get close to your accuracy.

Most PD meters are toleranced for a range of fluids or specificially engineered for one fluid which is where they deliver the best accuracy.

I think your best bet is to forget PD meters or revise your accuracy requirements.

Most PD meters do exhibit a flow dependent accuracy but the figure quoted is often the "envelope" value.

Piston gear and vane meters will all give you good accuracy dependent on the manufacturer and the working tolerances and for that you may have to specify the viscosity. SO though you see 0.5%, the repeatability is often significantly better at constant conditions of temperature and viscosity.

The variation in performance with flow is a function of the working tolerances and the fluid viscosity. Increased temperature not only reduces the viscosity it also usually opens up the tolerances and increases the swept volume.
PD meters often have a mechanical register so there is only one scaling factor used in the gear train. Their accuracy will be affected by temperature and viscosity. If you do use a PD meter you should choose one with a high resolution pulse output and have it calibrated on your fluid over a range of different flowrates to linearise it. This will get you much closer to what you want. Of course, you can calibrate yourself if you do follow this route.




JMW

http://www.ViscoAnalyser.com

 

[gt6racer2]

Thank you for the responses. I have made a solution based upon the constraints as follows : As I'm looking to check for good fill ( ie how much air is in the system ), I can measure the fluid going in and compare to known system volume as was the original plan. However, as I have a closed system I can also measure the air volume directly. I'll do this by filling the system under pressure, but then venting to atmospheric. I can then study the volume introduced /pressure relationship to deduce the air volume. As I'm looking for 1% of air or less, this volume will be only 40cc, and a meter with even 0.5% accuracy would be adequate.
Thanks for the advice ( to find a less demanding measure )which helped me find the solution. Andrew

 

[ApC2Kp]

gt6racer2,

If you are needing to confirm that volume was filled, is it possible to consider a weigh system for the hydraulic unit?

The extreme accuracy flow test sytems will use weigh tanks.

Some process vessels will have a weigh tank to precisely measure ingredients for 'exact' reactions to minimize any un-reacted hazardous chemical. Weigh systems are sensitive to vibrations (motion), wind loads, piping thermal expansion, and even a mechanic sitting on vessel during his lunch break. A weigh system might not be applicable for your equipment configuration.

 

[gt6racer2]

Thanks for the idea, but the system will already be a part of a vehicle when we fill it, so my system mass is insignificant.

 

[unclesyd]

Can you weight the oil supply tank before and after filling?