7cc/min flowmeter

How about considering the 'Lubricators' which are used in reciprocating compressors? They are capable of injecting very small quantity of oil and can be adjusted.

I was going to wait until I read up on SAE grades and viscosity equivalents but I'm too lazy now. I don't know how thick your viscosity is but you might try a peristaltic pump. I've seen them used for injecting fluids into patient's veins. The flow rate is very slow so this might be fine for your application. One other thing though. If your fluid is dirty, this might not be applicable.

.

I filled a glass with water and fixed my laser optical mouse to the outside. I moved a spoon over the area of the laser lense from inside the glass. There was no response. Would an optical laser similar to my mouse register movement if the laser lens was exposed to the water and spoon?

.y

7cc/minute is not that low. You can buy a rotameter from Brooks Instruments or others for this. You will need to do a viscosity correction of the reading, but if the temperature is constant, you can calibrate it out with your present system at first. Arrangements exist for measurement of the float position within rotameters, so you can do closed loop control (carefully) if you so desire.

Bernie Katz

Finding the right flowmeter with electronic output for your closed loop application is problematical.

However you could relatively easily fashion an closed loop system around a load cell based or other electronic weighing apparatus, performing dM/dt for rate, and outputting a control signal to a motor driving a peristaltic or positive displacement pump. Better than 1% accuracy over a minute should be achievable, and better accuracies over longer time periods.

The major advantage of a change in mass based system is that the longer it is running, the higher the total accuracy over the whole interval that can be obtained using the right algorithms, whereas errors in a flowmeter accumulate over time, (although you can calibrate them over a long interval).

But then, I'm biased, having a patent on a load cell rate monitoring device.

Greg

One of the ways of doing this may be to use a gear-pump and to control the speed of the motor to achieve the desired flowrate.

20-odd years ago this method was in use to control the flows of materials used in photographic film coating, and the flowrates were an order of magnitude higher than those in the posting.

Thanks everyone for replies.

The flowmeter will form part of a test rig that calibrates small oil pumps. The calibration will be done automatically by closed loop control (Labview and NI DAQ) on a small flow control valve that is already fitted to the oil pump. The acceptable flow rate being in the range of 6.9cc/min to 7.1cc/min. The total time given for each oil pump test and calibration is 7 minutes excluding operator load/unload time.

I have asked Brooks Instruments if they have anything suitable so fingers crossed,

Cheers John

If you're using a Labview programmed customized system, here goes a solution that works in a jet fuel test cell with similar equipment. It has less viscocity, so you'll encounter actually an easier application:

1. Choose a good flowmeter (turbine type one may be OK) from the lowest range. There are lots... Even if you're marginal in spec.

2. Instead of reading the frequency of the output signal a turbine gives, read the period of the wave, and calibrate your test stand based on it. You're gonna be able to get much more precise readings in the lowest range.

I've seen a system working from period reading in low flows, changing to normal frequency reading in high flows fro years without problem. Just make a good calibration manual for the folks...

But, actually, your original mass mesurement over time is by far the cheaper and most precise method.

Sorry, but I can't tell you a certain product to measure such tiny flow rate. But please be aware that the temperature dependent viscosity does not allow to use flow metering concepts suitable for water-like fluids without significant loss in precision.

From experience I would recommend flow meter designs based on "volume" measurement. Comfortable instruments transforming the rotation of the meter wheel in a frequecy counting. The actual frequency can be scaled as a flow indication directly or (more common) the frequency is transformed to a 4 to 20 mA Signal.

Those kind of "volumetric" flow meters can be of very high precision. So I guess, for the very small flow rates you are looking after you should find suppliers related with the chemical industry.

The other point is: do you need to ensure a (fix) flow rate of about 7 ccm, or do you need to clontrol such flow rate. In first case I would agree in already placed recommendations for injection systems (lubrication technology).

Albert

Yes the valve fitted to the oil pump will be adjusted automatically until it flows at 7cc/min. Then an anti-Tamper seal is fitted over the valve before being fitted to its host engine.

I did originally try searches for Lab equipment but had no luck. I will try again using volumetric flow in the search and also look at lubrication injection systems.

Cheers John

I feel you can monitor flow using MASS FLOW METER in which mass of the fluid is measured irrespective their densities / specific gravities.

Limbkar

Coriolis mass flow meters are highly accurate devices that would work great for your application. We used Micro-Master here in the states for paint flow monitoring. They had great engineering and field support. The meter will output the flow rate and provide automatic temperature compensation.

I would like to caution you on reusing the oil. If the reused oil has a lot of entrained air, it will need to be degassed via vacuum, or left undisturbed for x number of hours/days. We were discharging a fluid under high pressure into a tank for reuse and found the discharge fluid driving so much air into the fluid in the tank it was unusable for accurate results.

Hi all

Back to square one. Tried several flow meter companies and in all cases so far the support has been useless. All those contacted (including companies mentioned in this thread) said they had something suitable but seemed to give up with low flow rate and oil being the measured fluid.

So I guess the best solution would be to measure the mass of the oil flowed over a period of time whilst automatically adjusting the flow rate. Does anyone know if a commercial unit is available that can carry out this type of mass measument (not Coriolis, tried that route and technique fell over with the use of SAE 40 oil)

Cheers John