Flow Meters in Parallel

The spinning of the water in the chamber is used to divert a small portion of the fluid past the meter. (It is not known why it is called a Coriolis meter ). The accuracy of the split may be less at higher flows.

Using 2 I identical meters may result in better accuracy and in addition a difference in measurement may indicate other problems.

Different sizes can also be required to handle varying flows.

In water metering to buildings a big and small meter are often used in parallel. (big for bulk and small for the trickle flow)

Note that 2 identical looking meters may in fact have a different split ratio in the "Coriolis" chamber.

A Coriolis meter is called that because it uses the Coriolis effect, and actually measures that apparent force. G. Coriolis first described this psuedo force that is used to describe objects motion in a rotating reference frame. That is why the first coriolis flow meters had the liquid travel in huge circular paths. Some of the first ones, for just a 2" tubing run, were about 3' tall. now they suffice with just a small bow in them.

The direction of spin is caused by the construction and not by the Coriolis "force". If it was the meter won't work on or below the equator.

It should not be called a Coriolis meter.

Beg to disagree, the coriolis flow meter does work by coriolis effect. The coriolis effect unforturnately got linked to earth's rotation, but the application is beyond this.

Th coriolis effect is the apparant deflection of an moving object when viewed from a rotating frame.

The coriolis force is the force perpendicular to the velocity of body when the newtons laws are converted to polar (rotating) reference frame.

In coriolis flow meters, an ultrasonic vibration is passed throug the fluid (and in general case , the pipe/tube being circular, the vibration provides the circular reference frame. The changes in the frequency, phase etc of the signal are afunction of the flow rate.

This is from the literature of the coriolis flow meters we procure/

The only applications where I've seen two flowmeters in parallel were for those where continuous operation is necessary. If one flowmeter goes bad or needs to be calibrated (requiring physical removal), the operation may continue using the remaining one.

regards,

Vulcan

I disagree with your "the only applications ... were for those where continuous operation is necessary.

You can have several meters in parallel to cover a large flowrange.

You normally size a metering system this way :

2 times 100% of max flow

3 times 50%

4 times 33%, etc..

I didn't say that it can't be done.

Okay, the application says that the pumps have a capacity of 80,000 bpd. This means that the flow is usually below this point, maybe even half. Each flowmeter is rated at 84,000 bpd so one is more than enough to handle the flow.

If the flowrate is more than the biggest flowmeter available on the market, then, yes, you might be forced to use more than one. This is not the case here.

regards,

Vulcan

Welcome to Cr4.

GA from me,

It is simply to use one meter to do the job and the other as a spare, and as you notice from P&ID there are an isolating valves to fulfill that requirement.

Note: Refer to your P&ID drawing, the arrows of fluid flow downstream of meters must be reversed.

Vulcan is correct as far as I know, the only real way to calibrate these things is to take them out and send them to a flow lab. Therefore, you need two if you can't take your line down to fix a meter. Otherwise, all they can do is zero them by blocking them in (note if your block valves leak you will have issues).

If the intention is to detect if a meter is going bad, two meters connected in series is better for comparison than parallel meters. When connected in series, you know that the flow through them is exactly the same. In a parallel connection, the installation will have to be precise in order to assure exact same flow through the two flowmeters.

From your figures, the individual flowmeters have about the same flowrate as the pumps. Halving the flow between two meters will put the flow into the lower half of the meter's range. The upper half will never be reached, much less exceeded. That puts the majority of your flow in the less-accurate low-flow region of the meters.

So, no, I don't think the purpose of having two meters in parallel is anything other than redundancy.

regards,

Vulcan

I agree with your point "two meters in series" provides a better failure detection.

But if one meter is down, you must stop the flow to remove it unless you have a bypass line, which bypass flow will not be metered.

So meters in parallel provides a good compromise.

Best engineering is to have a Z config or a master meter.

Basically the Z config consists in having both meters in parallel most of the time. You can run a periodic control of your meters by rearranging the open/closed valves to set the two meters in series. In term of piping, you will need a bypass line with an isolation valve between the downstream side of the upstream meter and the upstream side of the downstream meter.

Master meter is used when recalibrating on the field the meters. It is a stand-by line. It allows you to move one meter for recalibration instead of two or three. Basically you run the same flow of fluid in the proved meter and the master meter, both running in series. You determine the new meter factor and reset it at the flowcomputer. Metering flowcomputers offer this feature.

In the present case, the piping arrangement doesn't plan for both Z and master meter config anyway.

Thanks for all the Inputs

Regards

Jose

hello my friend

maybe one flowmeter is for the control (fic) and the other one for the protection of the unit (trip). This situation is very common lately because of the safety.

I agree with Mr.Abdel Halem. Both meters have isolation Valves so anything goes wrong with one the other takes over to ensure constant & continuous flow data. In furnace oil pumps we install 2 strainers in parallel so that we switch over while cleaning one.