How to Calculate Pressure Drop in a Multi-Valve Air System?

In summary, the main question is whether or not it is possible to calculate the drop in pressure when opening a valve in a system with multiple smaller lines attached to a main steel pipe. The answer is yes, but it depends on the precision desired and there are many factors that may affect the pressure drop, such as the type and dimensions of the pipes and valves. To get a general idea, it is recommended to consult resources such as Wikipedia or the Engineering Toolbox website. The key to calculating the pressure drop is determining the flow rate, which can be found through the ideal gas law or by referring to the specifications of the compressor.
  • #1
5150racecar
2
0
Hello, I’ve seen a few posts regarding this topic but I can’t seem to grasp the concept of it. I have a main steel pipe x diameter providing 100psi of air to 6 smaller lines attached to it. At the end of these lines are valves. Is there a way to calculate the drop in pressure if I opened up 1 valve ranging from 0-60% if I know the orifice diameter? Moreover, could I find the drop in pressure if I open up multiple valves? Much help is appreciated.
 
Engineering news on Phys.org
  • #2
I am new to this forum and I do not know what has been posted as yet. Out of my practice as mechanical engineer I would answer your question with a clear yes and no and it depends...

Yes means, of course you can compute the pressure drop, provided you have all the data needed. And it depends on the precision you want to achieve.

There are a lot of textbooks around, that give you equations and parameters for the loss in pressure for flow through pipes and T-pieces of pipe other connections, valvesand such. But I found the results give some idea on what to expect for the actual pressure loss you see in real life depends on many params that usually are not modeled in the textbook's params. Like make of T-pieces, their radii, their finish. Or the power of the source to maintain the nominal pressure at increased flow. And ... and ... and...

I guess to have some minimum precision you will have to perform some tests on the pressure loss coefficients of the components of your system.
 
  • #3
Thanks for your reply NdotA. I'm not necessarily looking at absolute numbers. I'm just looking to see what effect opening and closing valves have on the system, and the other pipe lines. I unfortunately do not have access to textbooks, I was hoping to find a good website talking about this topic, if you could please direct me to one that would be very helpful.
 
  • #4
If you do not have access to printed books, I think best would be to start in Wikipedia. Look for the article 'Pneumatics' there, which gives anumber of leads to other references.
 
  • #5
Someone correct me if I'm wrong, but I think this summarizes the general approach:

Lets say you have a pressurized cylinder or a compressor up the line. If you just turn it on without letting a valve open, it will just build up pressure until it can't do any more. When you let a valve open, you'll get some airflow through the pipe, and some friction resisting it. The more friction, the more pressure loss. Friction ultimately depends on the flow rate of air, and the type and dimensions of the pipe. That flow rate, in turn, depends on the amount of pressure you've got in your system. Now, if you've got different sized pipes in series, then you just figure out the pressure drop in each section, then add up all the respective pressure drops.

You can find a lovely chart here:
http://www.engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html

The key is figuring out what flow rate to use. The units of flow rate will be CFM (english units). Flow rate is loosely governed by the ideal gas law PV=mRT (where V is flow rate, m is mass flow rate, T is temperature, and R is a constant, found on a chart), but in all reality you just have to look at the specs on the compressor. The compressor should have a rating on it telling what the flow rate is at each pressure. You can probably use the starting pressure (100) to figure that out. If the resulting pressure drop is more than about 5%, you may want to use that answer to back-calculate the flow rate, and re-calculate.
 

1. What is air pressure in a pipe system?

Air pressure in a pipe system refers to the force exerted by the air inside the pipes, which helps to move the fluids or gases within the system. This pressure is created by compressing the air and can be measured using a pressure gauge.

2. Why is air pressure important in a pipe system?

Air pressure is important in a pipe system because it helps to maintain the flow of fluids or gases and prevents them from becoming stagnant. It also plays a crucial role in the operation of pumps and other equipment in the system.

3. How does air pressure affect the flow rate in a pipe system?

Air pressure has a direct impact on the flow rate in a pipe system. Higher air pressure can increase the flow rate, while lower air pressure can decrease it. This is because air pressure helps to push the fluids or gases through the pipes.

4. How do you calculate air pressure in a pipe system?

Air pressure in a pipe system can be calculated using the ideal gas law, which states that pressure is equal to the product of the number of moles of gas, gas constant, and temperature, divided by the volume of the system. Other factors, such as elevation, pipe diameter, and fluid density, may also affect the calculation.

5. What are the common causes of changes in air pressure in a pipe system?

Changes in air pressure in a pipe system can be caused by various factors, including changes in temperature, elevation, or the addition or removal of fluids or gases in the system. Other factors such as leaks, blockages, or faulty equipment can also contribute to changes in air pressure.

Similar threads

Replies
2
Views
154
Replies
5
Views
909
  • Mechanical Engineering
Replies
5
Views
1K
Replies
3
Views
190
Replies
1
Views
2K
  • Mechanical Engineering
Replies
2
Views
793
Replies
16
Views
2K
Replies
3
Views
876
Replies
3
Views
1K
  • Mechanical Engineering
Replies
28
Views
2K
Back
Top