Application Assistance

[RonMed]

Can anyone help me with my application?

Here are the components and order that the DI water goes through:

I have incoming DI water (55 psi, 70 deg F) going through 1/2" teflon tubing that is regulated at 30 psi. Then there is a needle valve (H2O In valve). From the valve, it goes through the part and there are pressure transducers before the part and after the part measuring the pressure drop. Then there is another needle valve (H2O Out valve) and it goes to a rotameter. From the rotameter, it drains to a sink. The process includes adjusting the "H2O In Valve" to a certain flow rate (ranges from 0.8 to 4.5 LPM) and then adjusting the "H2O Out Valve" creating a back pressure on the pressure transducer (after the part) to 150 mmHg. My goal is to replace the rotameter with a digital gage to improve the repeatability (at least 3% accuracy). So far I have replaced the rotameter with a McMillian digital gage (3/8" OD fitting) and it produced a back pressure at the higher flow of 4.5 LPM (too high of a pressure at the pressure transducer after the part). Also, does the pressure drop of the gage that I purchase apply in this situation if I am measuring the pressure differential upstream? Can anyone recommend a digital gage that can work with these flows and pressure and not produce a back pressure? In addition, if there is an automatic flow controller out there where I would set the flow rate and I would only have to adjust to the correct pressure, I would be open to suggestions for that too.

 

[hydrae]

RonMed

If you have a large budget, I would look at a magentic flow meter, look at a 1/4" to 1/2" size range, mag meters have no internal parts to create restrictions, but they do require a small amount of contaminate in the process stream, verify with the manufactorer that your DI water is not to clean for their meter. The meter does require power 120VAC or 24VDC and will produce a 4-20 mA flow signal if you desire.

For back pressure, (I assume you require this at 150mmHg) is it possible to route the discharge up 7 ft above your process and overflow to atmoshere into a collection tube. This would create a very constant backpressure without the outlet control valve, this may also stabilize the flows so you can get the repeatability you are looking for.

For flow control I would need more information. Does the device actively change the flow path, or are the different flows an operator adjustment?

Hope this helps

Hydrae

 

[jmw]

Rotameters are not necessarily only available at 3% accuracy nor only read using viscual observation of the float against the scale. High precision instruments are available with regulators to control the flowrate and with analogue outputs which can be displayed using digital indicators. Try a search under KDG or under Rotameter.