2025-11
04How to choose the pipe diameter when designing the gas circuit?
Background Introduction
One of the most headache inducing issues in high-end manufacturing for gas path design is: "How thick should this pipe be
Selected carefully, the airflow resistance is too high, the pressure drops down slowly, and the end equipment cannot eat enough and strikes directly; Choosing too coarse, wasting materials, increasing costs, and occupying space, is really not worth the loss.
Where does the traffic come from?
Let's start with the basic formula of flow. For circular pipelines (in the vast majority of cases), the calculation of gas volume flow rate is essentially:
Flow rate=cross-sectional area of pipeline × flow velocity
Q=πd²/4·ν
This means that the flow rate is proportional to the square of the pipe diameter and proportional to the flow velocity. This is an exponential relationship:
Double the diameter of the pipe (e.g. 10mm → 20mm), and the flow capacity becomes four times the original.
If the flow rate doubles, the flow rate will also double.
Illustrate with examples
A pipe with an inner diameter of 10mm has a flow rate of approximately 47.1 L/min at a flow rate of 10m/s.
If the pipe diameter is changed to 20mm, the flow rate will jump to about 188.4 L/min at the same flow rate.
Note: This flow rate is the volumetric flow rate under operating conditions. To convert it to the flow rate under standard conditions (mass flow), it is
necessary to make corrections based on the pressure and temperature inside the pipeline.
Ubiquitous pressure drop
However, in actual pipeline systems, the above calculations cannot be simply carried out. Gas viscosity, pipe wall roughness and length, and various pipe valves can all have an impact on gas flow.
Gas viscosity
The higher the viscosity, the greater the gas flow resistance.
pipe length
The longer the pipeline, the greater the friction loss.
pipe valve fittings
Bends, valves, and other components can generate local resistance. A 90 degree standard elbow may have a resistance equivalent to 5-10 times the length of a straight pipe!
All these obstacles ultimately translate into pressuer dropes that we do not want to see. Excessive pressuer drop can directly lead to low efficiency, decreased control accuracy, and other issues, making it the "number one public enemy" in air circuit design.
How to quickly lock the pipe diameter with experience?
Faced with complex theoretical calculations, engineers have already summarized safe experience values. The "Process Pipeline Installation Design Manual" provides us with a recommended range of compressed air flow rate, which is of great reference value:
So, how do I use this table?
1. Confirm parameters
Clarify your system's work pressure and demand flow.
2. Check the table and set the speed
Select a suitable flow rate from the above table based on work pressure (it is recommended to take a middle or lower value for the main pipeline to leave room for excess).
3. Reverse calculation of pipe diameter
By using the formula pipeline cross-sectional area=flow rate/flow velocity, the required pipe diameter size can be inferred.
This flow rate range has fully considered safety margins and is a validated and highly reliable design starting point.
summary
Excellent gas path design is the product of theoretical calculations, engineering experience, and specific requirements. Only by ensuring safety, stability, and efficiency can the most economical and reasonable pipe diameter selection be made.