Proper orientation of restricting orifice | think principle

restricting orifice
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It is quite a maniac content that explains the orientation of the restricting orifice.

When you think of an orifice , you probably think of flow calculation, but there are also scenes where you worry about the installation direction at the construction and site level.

Surprisingly, many people do not know that there is a concept of orifice direction.

This applies not only to mechanical engineers, but also to those who have mastered chemical engineering.

On the contrary, it means that you have a certain amount of engineering power just by being able to properly explain the orientation of the orifice.

It’s your chance.

Restrictive orifice for head delivery

In this example, it is assumed that an orifice is attached to the head liquid transfer line.

Such is the case.

flow restricting orifice

A typical example of adding an orifice would be the following case.

  • continuous plant
  • pump circulation line
  • Secure minimum flow

This is a textbook example.

Batch-type chemical plants do not often have this example, so I will introduce this example as an occasional example.

You want to keep the flow rate constant when dripping the liquid with the head, but it is difficult to control with just a control valve.

This is the pattern.

The essential cause is that the pipe or valve diameter is too large for the required flow rate .

In batch operations with many switchovers, there are troublesome cases where the same chemical is fed from the same tank, but the flow rate is completely different depending on the production item.

Here, instead of trying to match the flow rate with the pipe diameter, you may try to rely on the orifice.

Some production plants may support manual valve opening adjustment. This is where there is a technical difference.

Here, the orifice has a “mounting direction”, and the problem is in which direction it should be mounted.

Direction of the control orifice to the expanding side

In conclusion, the orifice should be oriented in the direction of ” expansion “.

It looks like below.


An orifice is a device for narrowing the passage of liquid, and consists of the following parts.

  • Piping diameter
  • Orifice diameter
  • Tubing and orifice sizing taper

In principle, there are two patterns to attach this “taper” on the upstream side or on the downstream side.

Here, it is common to taper “downstream” or “in the direction of expansion” .

Expanding and contracting pressure loss

Why is the orifice oriented in the direction of expansion?

This is related to pressure loss .

Let’s take a look at two cases: the “reducing” side with the orifice taper on the upstream side, and the “expanding” side with the taper on the downstream side.

enlargement and reduction (orifice)

In terms of pressure loss , the right “expansion” side is higher .

Is this easy to understand if you imagine a flow pattern?

There is a swirling flow in the flow pattern when expanding .

This vortex is in the direction of flow and in the direction of counterflow, and acts as resistance.

This resistance appears in the form of pressure loss.

Actually, changing the direction of the orifice and letting the liquid flow while the liquid level in the tank is fixed makes it easier to understand.

The valve opening of the control valve changes slightly.

If the taper is installed with a contraction flow on the upstream side, the throttling of the control valve will be strong.

In this case, the valve opening of the adjustment valve may not be sufficient and adjustment may not be possible.

Considering the role of the orifice to intentionally create pressure loss,taper downstreamYou should put it on!

Precautions for installation

Although the restriction orifice is oriented, it can be misplaced in the field.

In order to lower the probability even a little, let’s mark the orifice.

Anything that makes the flow direction stand out is fine.

It is a good idea to attach a handle to the side and indicate the direction so that it can be checked even if it is set in the pipe.

Humans make mistakes when there are 2 pattern choices.

The restriction orifice must be installed after properly observing the piping flow, but it is quite difficult to see the piping flow during construction.

There are many cases where the flow itself written in the piping diagram or P&ID is wrong.

The construction company will be very skeptical about that area and will do the construction, but it is natural to worry if the original materials are wrong.

Super application of orifice

The orientation of the orifice is usually on the side with less pressure loss.

However, sometimes it is better to put it in the opposite direction.

That is dripping at a small flow rate .

If 20A is too large a flow rate and glass lining or fluorine resin lining piping is used due to corrosiveness, there is a limit to control with a regulating valve.

I really want to make it 10 mm or less, but it’s a pattern that I can’t.

In such a case, an orifice is added, but it does not always work well.

If you have an orifice in a suitable flow but it doesn’t work and you want to reduce the flow further, try installing it in the opposite direction .

You may end up with something.



Introduced the installation orientation and pressure loss of the restriction orifice.

Orifice for head liquid transfer ・The orifice direction expands to the downstream side.The orifice direction expands to the downstream side.

Considering the role of the orifice to intentionally create pressure loss, the taper should be on the downstream side.

Please feel free to post your worries, questions, and questions about the design, maintenance, and operation of chemical plants in the comments section. (The comment section is at the bottom of this article.)

*I will read all the comments and answer them seriously.