# Pressure, diameter and flow in a pneumatic system

• Simple_One
In summary, the author is looking to determine the impact of changing the internal diameter of the hose/fitting system in a compressed air system. The starting information is as follows... Compressed air tank outlet diameter: 3/8" ID (9.525mm) Compressed air tank pressure: 160 psi (1,103.16 kPa) Compressed air tank size: 1.94231 cubic feet (55L) Piping and fitting size: 1/4" ID (6.35mm) Hose length: 20m The system is fitted with a 1/4" ID pressure regulator, straight after the outlet from the air reciever, and this regulator is set to 90 PSI. The question is, since
Simple_One
Hi everyone,

I have a problem (which is likely to be fairly simple), which I need a hand to resolve. I'm trying to determine the impact of changing the internal diameter of the hose/fitting system in a compressed air system (in this case a portable compressor, with an inbuilt air receiver).

The starting information is as follows...
Compressed air tank outlet diameter: 3/8" ID (9.525mm)
Compressed air tank pressure: 160 psi (1,103.16 kPa)
Compressed air tank size: 1.94231 cubic feet (55L)
Piping and fitting size: 1/4" ID (6.35mm)
Hose length: 20m

The system is fitted with a 1/4" ID pressure regulator, straight after the outlet from the air reciever, and this regulator is set to 90 PSI.

The question is, since the receiver has a 3/8 outlet but is being constricted by the air hose and fittings 1/4 ID, how much extra air flow could I expect to gain by moving to a 3/8 ID hose and fitting system?

Somewhat more specifically, I'm looking at this from the point of the peak torque output from an impact wrench. I'm not certain what factors influence the torque output of these tools, but most of them list a peak air requirement (in L/min or cubic feet per minute) which I assume would correlate with the published peak torque (up to the devices engineered safety limits etc). Most have a maximum operating pressure of 90 PSI, hence the regulator setting.

All other things being equal (and assuming i don't exceed any engineered limits on the pneumatic tool), I would anticipate better performance from the tool if the air hose and fitting system all the way from the receiver outlet was of a larger ID (3/8 vs 1/4), the real question is, how much better...?

So, should I take it from the lack of response that it's not possible to calculate what I'm seeking with the information provided, or that it is unclear what I'm asking?

To calculate the pressure drop vs flow you need the friction factor for the hose. This is something I don't know. Have you looked at the compressor / hose / tool manufacturer's websites? They should have charts or tables or at least "thumb rules" for system design. These might be in the form of recommended hose diameter vs hose length. I think a 20 meter hose is on the long side, if you really need hose that long it would be better to use a larger diameter. Another option is to use hard pipe for most of the length, and put the regulator and hose connection closer to the work. This allows higher pressure closer to the work and shorter hose.

Hi, thanks for the advice. Unfortunately this system is a portable one so fixed tubing isn't an option, otherwise I would be doing it :)

I'm going to get a small pressure gauge that I can fit inline at the end of the current system so I can measure pressure drop across the current setup. If it seems to be a significant drop, then I'll just suck up the cost and upgrade the whole show to 3/8" or maybe even 1/2" all the way through. Then I know that the air delivery system is as good as it can be (within practical limits for portability etc) and if more air is needed, I can just swap the whole show on to a larger compressor.

I'll do a rudimentary calculation based on this data as well:
http://www.airtx.com/recommended-air-hoses.htm

Thanks!

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Air tool hose size
Got lots of hits. I'd say some of the advise is good and some is misguided. But if you read thru you can make up your own mind. Me, I'd get some 3/8 hose. You don't necessarily have to change all the fittings since a lot of the losses are in the hose.

Similar question, no real answers, more focused on the air tool than the flow/pressure, despite what the OP asked. I'm going to stick with the obvious theory that larger diameter equals more goodness. How much extra goodness I still haven't determined; but definitely extra goodness.

I'll also cut the existing 20m hose in half and add another quick connect, at least that way I'm only incurring the extra pressure drop when it's necessary with that hose.

This link has some handy tables relating to hose diameters, flow and pressure drop:
http://www.airtx.com/recommended-air-hoses.htm

Looks like 1/2 ID would always work fine for my purposes. I'll save some pennies and then go for that in the longer run.

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## 1. What is the relationship between pressure and flow in a pneumatic system?

Pressure and flow in a pneumatic system are inversely related. This means that as pressure increases, flow decreases, and vice versa. This relationship is described by Boyle's Law, which states that in a closed system, the product of pressure and volume is a constant.

## 2. How does the diameter of a pneumatic system affect its performance?

The diameter of a pneumatic system can greatly affect its performance. A larger diameter allows for a greater volume of air to flow through, resulting in higher flow rates and faster response times. However, a larger diameter also means a larger volume to pressurize, which can lead to increased energy consumption. It is important to carefully consider the diameter of a pneumatic system to balance performance and efficiency.

## 3. What is the maximum pressure that a pneumatic system can handle?

The maximum pressure that a pneumatic system can handle depends on its design and components. Most pneumatic systems are designed to handle pressures up to 150 psi, but some specialized systems can handle pressures up to 3000 psi. It is important to always check the specifications and limitations of a pneumatic system before use to ensure safe operation.

## 4. How do you calculate the flow rate in a pneumatic system?

The flow rate in a pneumatic system can be calculated using the following formula: Q = (A * V * C) / t. Q is the flow rate in cubic feet per minute (CFM), A is the cross-sectional area of the system in square feet, V is the average velocity of the air in feet per minute, C is a coefficient of flow (typically 0.9 for a well-designed system), and t is the time in minutes.

## 5. What factors can affect the pressure and flow in a pneumatic system?

There are several factors that can affect the pressure and flow in a pneumatic system. These include the size and design of the system, the type and condition of the components, the air supply and source pressure, and any restrictions or blockages in the system. It is important to regularly maintain and monitor a pneumatic system to ensure optimal performance and safety.

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