Standard Flow rate helps deciding pipe diameter | time saving

Flow rate
記事内に広告が含まれています。This article contains advertisements.

I will explain the approximate calculation of pipe diameter and flow rate that are useful on site.

If engineers can use this way of thinking in the field, it will be very useful when receiving consultations in the field.

If I go to the site without thinking about it, I will suddenly receive a consultation from the production manager saying, “It was just right!”

Most of the consultations are about driving troubles. There are many contents that “things do not flow”, and the pump is likely to be the cause.

Especially in old plants, there are many cases where troubles occurred because they were not properly designed, and they can be easily solved with the current solid design.

Just knowing the relationship between the pipe diameter and the flow rate, and the relationship with the pump flow rate, will make it possible to respond immediately, and the trust of the manufacturing section will increase at once.

It will make it easier for you to control your work, and it will also be advantageous for your career, so it is a content that you definitely want to keep in mind.

Approximate calculation of pipe diameter and flow rate

We will introduce the approximate calculation method of pipe diameter and flow rate.

It is a very important concept for batch chemical plants, and includes contents that can be used by memorization.

There are engineers who have been in charge of mechanical design for nearly 10 years but cannot immediately respond to troubles related to this way of thinking.

I can’t stress it too much, so I would like to explain it with various approaches.

Illustration of a water supply that is left out

Standard flow rate

The concept of standard flow velocity is very important in batch chemical plants.

Standardization and modularization will become trends in batch chemical plants in the future.

  • Use the same equipment on multiple production lines
  • Usage conditions (flow rate, pressure, temperature) are different on this production line

The important point of a batch-type chemical plant is that it must adapt to multiple patterns, unlike a continuous plant that can be individually optimized.

The concept of standard flow velocity is very useful in determining the diameter around the pump.

For liquids, consider 1 to 2 m/s.

The diameter of the gas line is also almost determined by the concept of standard flow velocity.

It is even possible to select 80 to 90% of batch chemical plant diameters based on the concept of standard flow velocity alone.

Standard flow rate

  • Liquid 1-2m/s
  • Gas 10m/s
  • Steam 20-30m/s

Diameter x flow velocity = flow rate

We will introduce how to calculate the flow rate from the diameter and flow velocity.

However, it is a very simple formula.

Q =PiFourA.v2

Just use this formula.

Since there are two parameters and it is difficult to use for immediate determination on site, the flow velocity is fixed.

This is the concept of standard flow velocity.

Memorize some standard numbers. Two is enough.

Basics of diameter and flow rate

  • 110L/min at 40A
  • 170L/min at 50A

That’s all there is to it.

After that, it can be applied with a little mental arithmetic.

  • 25A → 1/4 times 50A → Approx. 40L/min
  • 80A → 4 times 40A → Approx. 440L/min
  • 100A → 4 times 50A → Approx. 680L/min

As long as the standard flow velocity is determined, the relationship that the flow rate is proportional to the square of the aperture will come into play.

Applications will expand if only two numbers can be used at the field level.

Example of standard flow rate

Let us summarize the results of the calculations based on the example introduced above.


Flow rate problems are mostly liquids, and about 80% of them are solved with the main 40 to 50A.

Gas and steam can also be designed with the same concept, but I don’t think there is much frequency in relational calculations that are conscious of the standard flow rate.

Rather than that, more serious calculations are performed at the P&ID and equipment design stages.

Example of trouble at a batch chemical plant

Pumps account for more than 50% of the problems that occur at batch chemical plants.

The problem that the liquid cannot be sent by the pump occurs especially in trial production.

It can easily happen if you neglect a basic and easy part of pump design.

For example, the following example can normally occur at the user’s design site.

I want to send a flow rate of 10L/min with a pump of 100L/min and a bore of 40A.

I understand your needs.

But if you have a little knowledge of pumps, you should be wondering if you can secure a minimum flow.

With a normal 100L/min pump, the minimum flow is about 20-30L/min.

It is not possible to send a small flow rate of 10L/min.

In this case, we take the method of sending little by little while circulating.

Also be careful.

A 100L/min pump will be operated under the following conditions.

  • circulation 90/min? ? A.
  • Liquid transfer 10L/min 40A

Originally, the diameter of the line that sends liquid with a 100L/min pump is designed at 40A based on the standard flow rate.

If you try to send it at 10L/min here, almost no pressure loss will occur.

If you have a 100L/min pump, you have to think that 90L/min other than 10L/min will flow through the circulation line.

The problem here is the pressure loss balance between the circulation line and the liquid transfer line.

In reality, it is forced to adjust with a manual valve , but there is a limit.

However, even with an automatic control valve , the CV value is too high to control.

In such cases, impeller cuts and restrictive orifices are relied upon.

The difficulty of a batch-type chemical plant is that it is not possible to simply design for one product line.

If you want to learn a little more…

This rough calculation is very useful in practice.

If you want to know a little more details, but you don’t have to introduce calculation software, the following books will be useful.

created by Rinker
¥4,180 (2024/02/29 14:45:09時点 楽天市場調べ-詳細)

For the calculation, we use detailed piping shape settings and pressure loss calculations.

In order to confirm the correctness of the results obtained by calculation, we will return to the basic formula, which is the principle principle.

This basic formula is exactly the rough calculation of this time.

Related article

Related information


I explained the rough calculation of the pipe diameter and flow rate that is useful on site.

Calculate the flow rate from the standard flow velocity, diameter and flow velocity, and check the required flow rate and pump flow rate.

Just memorizing two numbers, 110L/min at 40A and 170L/min at 50A, expands the applications.

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.