We have 6 Air compressor connected to 8" header. the existing flowmeter we have is DP with orifice plate which does not give us the vendor reading.

So, please advise what is the best flowmeter technology to use for compressed air and if it has to be compensated by Pressure or Temperature or Velocity.

 

I cannot advise on the flowmeter technology, but i'm sure you checked and if not, have you check the sizing of the orfice and the range of the dPT? How about the installation if the orfice? Enough straight pipe up and downstream?

If so, please ignore this post and I look forward to responses to your request.

Good day.

 

Hi,

Various type and ranges of flow rate transmitters are available from E+H (Endrauss+Hausser) products.

 

Yes, your orifice plate needs to be compensated for pressure and temperature. Orifice plates can be quite accurate if installed corectly.

Other options:

Pitot tube (often called Annubar)
Vortex Shedding

Both of those need to be installed corectly as well. Why not describe your existing installation, I'm sure some-one can help.

Regards
Roy

 

Yes, Orifice Plates are quite reliable flow metering device but do have few disadvantages like Permanent Pressure Drop, Impact on accuracy due to wear & tear of orifice edges, Maintainance etc. There are better technologies including Averaging Pitot Tube, Vortex, Thermal Mass Flow Meter etc which can be alternative choice against Orifice Plate. If the operating pressure & operating temperature swing is very large it is always recommended to compensate it for better Mass Flow Measurement. It is always recommended to re-calibrate orifice plate over 3 years to find out the new flow co-efficient & use the new flow co-efficient for DP Calculation.

On a 8" line & provided DP is the choice, I would highly recommend use of Averaging Pitot Tube with integrated RTD to get Mass Flow Rates else you can also look at Vortex & Thermal Mass as an alternative choices.

 

the best meter for compressor air application is VORTEX flow meter with PT compensation .. KROHNE MARSHALL, INDIA (FORBES MARSHALL) is manufacturing vortex flow meter with inbuilt Pressure and temperature transmitter for online density compensation (PT COMPENSATION)...

if the meter without PT compensation will cause the error ... and leads the measuring error 10 to 20 % based on the pressure and temp variation.

 

First of all which type flow meter is used by you is very important. Normally for air flow meter venturi type is very good for high flow low pressure measurement. And you have to very careful about ur DP range.

 

Hi Aimo,

The best option is thermal mass flowmeter. Installation is very easy with minimum modifications (just insert inline) and you have the mass flow ready. You can also get the volumetric flow but you need to do some calculations. In case you have some field bus (Profubus or Foundation Fieldbus) you can do it at the transmitter itself.

Vortex flowmeters act funny specially if you have large variation in flow and high temperature changes.

Averaging pitot with temperature and pressure compensation could do the job but installation requirements are so much. You need quiet large straight line upstream the meter and they can be very tricky.

Forget about orifice as they do not have a good turndown ratio and very much affected by temperature and pressure changes.

In a word, go for Thermal Mass Flowmeter!

Good luck,
Hamid

 

i recommend forbes marshall vortex flowmeters. we r using it

 

Hi,

I have seen lot of compressed air application where turbine flowmeter with pressure & temperature compensation is very successful. The results are quite impressive. As far as reliability concern it's a good technology to measure volumetric flow provided it needs a proper installation.

Nayan Mishra

 

Thermal mass can be quite troublesome if there is any entrained moisture because a tiny drop of water will have a significant effect on the thermal sensor.

Hamid is correct in saying orifice plates don't have a large turndown however if you make a mistake a new size of orifice plate is a lot less expensive than most other technologies. You also need to consider the cost of maintaining the differential pressure, it could be significant in a large system.

On a large compressor installation you likely have pressure and temperature signals which you can use for compensation.

Vortex meters on gas have a turndown of about 40:1