Flow Control

Hi

Since your question is very general the answer to it also can't be very specific unless more information provided.

First was wondering what N stands for beside your flow rate unit?

Second,your flow rate range as you have indicated is very wide, so the next problem encountering is the flow velocity and pipe diameter and friction losses.

Usually based on the allowable friction loss for different gases the pipe size vary based on differential flow rate( maximum and minimum).

so based on your end user required flow rate and the distance, as you have also mentioned provide required number of controller for each branch.

Good luck

If you want to measure the normalised volume of a gas I would suggest a mass flow meter as being the most suitable...

For the range of 1300litres/min down to 17 litres/min (80 m^3/hr to 1m^3/hr) there are several mass flowmeters which can easily cope with that turndown.

All that's needed is the accuracy or reading and loads of other effects to be able to select the right transducer for your application.

John.

One valve cannot work because of constant valve CV. Therefore make a split range final element where different valves are used each with the correct CV over a specific range. Adjust the controller to give the correct control force signal to each of the valves by splitting the control force signal (say 4 - 20mA) into (say) three ranges. Each valve is then sensitive to the appropriate range signal. Have used this succesfully.

To design control system also need to know ΔP across valve at both flows. Usually valve ΔP is higher at lower flow - reduced pipe friction, compressor running up curve, etc. Full range of Kv (or Cv in US) then given by min flow/max ΔP vs max flow/min ΔP, and is likely to be even greater than 1:80.

As you say, can't do this on one valve. I'd suggest 2 in parallel. If actual Kv range = say 100, design each for √100 = 10. Valve A for 1:10, valve B for 10:100. Control on A for low flow, with B closed. When A fully open, control on B up to max flow. Kv range 1:10 is well within range of a control valve.

Cheers....Codey

ARGON ===> REGULATOR ===> dP Flow Sensor ===> Valve ===> Rotameter

This set-up works well across a fairly good range if you size your orifice plate to cover the dP flow in your needed range. Bore sizes are available down to a very small diameter. Calibration and zero trim adjustments are quite simple to keep your process readings accurate. The rotameter will suit flow loops where the dynamics of the system are minimal, (ie SP adjustment is fairly uncommon). An alternative for dynamic control would be a dP secondary loop to control the flow in the primary loop in a cascade type set-up. Sizing will be crucial here again, and depending on the dynamics, you may be having to watch for stiction depending on pipe and supply distances as well as your control valve travel as you'll start to notice stem wear and slop over time. Another issue is you'll need more instrumentation. This can be done within a decent budget...Good Luck.

The flow rate has a turn down ration of 80 to 1....

You will be very lucky to get a turndown ration of 10 to 1 with an orifice plate and rotameter.

As the gas is reasonably pure i.e. Argon, a mass flowmeter would be ideal.

John.

I don't know if this will you, all you need is a regulator that can control the flow. You can surf on the web for more info.

Just another comment - some of the contributors appear to be answering a question that wasn't asked, ie about flow measurement, whereas question was about flow control. The flow controller could respond to various inputs, not necessarily a flow signal.

If you do need to measure the flow, as Electroman said, 1:80 can be done with a mass flowmeter. Spec sheet I have from FCI (1999 but if anything there'll be improvements since then) says 100:1 standard, 250:1 option. But if you use my suggestion of 2 control valves in parallel you could put a flowmeter in each leg, with lower turndown (and add the readings, naturally)

Cheers.....Codey