Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Restricted Orifice Working Principle.


This topic has been archived. This means that you cannot reply to this topic.
8 replies to this topic
Share this topic:
| More

#1 Faizan Wajid

Faizan Wajid

    Brand New Member

  • Members
  • 1 posts

Posted 31 January 2012 - 02:44 AM

Hi,

Can any one please explain me the working criteria of an RO. it reduces flow rate as well as pressure. how this is possible.?
A/C to relations pressure decreses with the increase of flow rate.
Can any one please give me the insight knowladge of it.

Regards

Mr. Faizan

#2 Dacs

Dacs

    Gold Member

  • Members
  • 387 posts

Posted 31 January 2012 - 03:30 AM

Restriction Orifice (RO) works by imposing pressure drop across the flow due to the constriction brought upon by the orifice.

It does not reduces the flowrate per se. It provides a pressure letdown and sized as such that for a given pressure drop, it will provide a certain flowrate.

Too large an orifice size, it will give you a higher flowrate than desired. Too small an orifice size, you'll choke your system and may even overpressure your upstream system.

#3 mohds23

mohds23

    Junior Member

  • Members
  • 13 posts

Posted 31 January 2012 - 07:22 AM

As name suggests, Restriction Orifice is used to create restriction in flow through a small opening and it restricts flow based on the principle of 'choked' flow.

When we say that flow is 'choked' means, further volumetric flow increment through opening is not possibly by increasing upstream pressure or decreasing downstream pressure.

I will try to explain the concept for RO application in process plants with following cases;

Case-1:Compressor scrubber liquid drain lines leading to condensate collection system: In such kind of application the purpose of RO is to provide a restriction in volumetric flow of gas(during gas blow-by condition), to avoid downstream system pressure buildup beyond a certain level.
RO opening is sized such that the back pressure at RO outlet during steady state condition of gas blow-by through RO and downstream system, remains within certain level to ensure choked flow condition (upstream press. / downstream press ratio between 1.7 to 2.1).

Case-2:Purge gas supply line to flare headers: In such application the purpose of RO is to provide nearly exact purge gas flow capacity ( which is difficult to ensure with pressure control valves) to maintain a required flow velocity in flare headers.
Adequately sized RO ensures back pressure at RO outlet within certain level to ensure choked flow condition (upstream press. / downstream press ratio between 1.7 to 2.1) and susequntly constant flow through the RO irrespective of upstream or downstream pressure fluctuations.

Case-3:Blowdown line of a pressure vessel: In such application the purpose of RO is to provide a restriction in volumetric flow of gas(during equipment blowdown condition), to avoid excessive depressurization and subsequent lower temperatures.

In all above cases, RO doesn't kill pressure directly but through restricting flow across it.
Hope this explanation is somewhat helpful.
For futher study of the subject you may refer to following topic in cheresources
http://www.cheresour...ual-conditions/

regards,
Sharique

#4 paulhorth

paulhorth

    Gold Member

  • ChE Plus Subscriber
  • 396 posts

Posted 01 February 2012 - 05:31 AM

Sharique,
While I agree with your comments I would add a couple of points:

When we say that flow is 'choked' means, further volumetric flow increment through opening is not possibly by increasing upstream pressure or decreasing downstream pressure.

That's not quite right. Even in choked flow, the mass flow is proportional to the UPSTREAM pressure, so raising the upstream pressure does increase the flow.

Second, restriction orifices are also used in liquid service, for example to provide a minimum flow recycle for a centrifugal pump.

To mohds: Think of a restriction orifice as like a valve, but welded at a fixed opening. That's all. The flow through it depends on the pressure across it, just like a valve.

Paul

#5 paulhorth

paulhorth

    Gold Member

  • ChE Plus Subscriber
  • 396 posts

Posted 01 February 2012 - 11:57 AM

Apologies, my comment

Think of a restriction orifice as like a valve,

was intended for Mr Faizan, the first poster, not mohds.

Paul

#6 sheiko

sheiko

    Gold Member

  • ChE Plus Subscriber
  • 732 posts

Posted 02 February 2012 - 07:34 AM

Paul,

Mohds was talking about volumetric flowrate....so he is right.

#7 paulhorth

paulhorth

    Gold Member

  • ChE Plus Subscriber
  • 396 posts

Posted 02 February 2012 - 08:49 AM

Sheiko,

For UPSTREAM volumetric flow, yes - for DOWNSTREAM volumetric flow, no.
But upstream volumetric flow is not usually what you are trying to limit.

Paul

#8 KIshor

KIshor

    Brand New Member

  • ChE Plus Subscriber
  • 7 posts

Posted 03 July 2012 - 05:05 AM


When we say flow is choked means only velocity is choked and not mass flow rate of gas.
Mass flow rate of gas can not be increased by decreasing downstream pressure but you can still increase mass flow by increasing upstream pressure.

#9 Jeff2013

Jeff2013

    Brand New Member

  • Members
  • 1 posts

Posted 02 August 2013 - 07:18 PM

Hi,

 

I came across this forum when searching for an answer to a question concerning LP Gas.

 

Some automobile systems (those with tanks located in passenger compartments); but, which have a sealed vapor box installed around the valving, require remote filling. Basically this consists of a fill line and a vent/80% liquid level line which are run to a remote double check and a spitter valve, respectively.

 

My question concerns the 80% fill line, and the use of a restricted orifice.

 

The 80% fill coupling includes a dip tube on the inside of the tank. The purpose of the dip tube is that at a volume of 80% during the fill process, liquid will enter the dip tube and exit the tank. In the case of tanks located in a truck bed, or in stationary configurations, that liquid will be discharged through a "spitter valve that is attached directly to the tank.

 

In the case of remote fill applications, a restricted orifice is required. In this case the liquid exits the tank, moves through a valve, through a high pressure hose, and out through the spitter valve located on the exterior of the passenger compartment. Typically the restricted orifice is located on the 80% dip tube coupling, in a separate nipple, or as part of the valve assembly attached to the coupling on the tank.

 

My question concerns the use of multiple restricted orifices in that system. Both orifices would be #54. One orifice would be located inside the tank and the other on the valve attached to the coupling leading from the tank. The orifices would be separated by approximately 1-1/2". The valve that threads into the coupling is 1/4" NPT. The approximate volume of the area between the two orifices would be 100 to 200 ccs. Normally the valve would be provided without the orifice due to the fact that there is an orifice inside the tank. In this case, however, the valve has a restricted orifice, too.

 

I have read that the purpose of the resticted orifice is to reduce flow by creating a pressure drop across the orifice. The purpose of this 80% arrangement is to alert the filling attendant that the tank has reached 80% fill (maximum capacity) and that the pump must be turned off.

 

Is this second orifice (the one in the valve) something to be concerned about in terms of restricting the flow too much. Or will the location of the two orifices within inches of one another be somewhat insignificant?

 

I was thinking about drilling the orifice out of the valve; but, I am afraid that the valve may not seat properly after doing that.

 

Thanks for any advice you might offer.

 

Jeff






Similar Topics