Blocked pipe = increased air velocity?

In summary, the conversation discusses the impact of blocking the intake of an air flow station on the FPM (feet per minute) and vacuum levels. The measurements show that blocking the intake leads to an increase in both the vacuum and velocity, and the question is raised about whether there is a conversion factor to account for this in the CFM (cubic feet per minute) equation. The flow station is located between the damper and fan on the intake side, and the measurements increase as the blockage becomes more severe. The individual also mentions that it would be difficult to measure velocity on the exhaust side and asks about the type of instrument being used for velocity measurement.
  • #1
radonbc
4
0
Blocking the intake of an air flow station I built results in the FPM shooting up along with the vacuum. ie: wide open both ends 4" pipe with inline fan reads . 5" wc / -190 pa / 3700 fpm on instruments monitoring intake pipe. Blocking the intake increases both the vacuum to -470 pa and increases the velocity to 5400 FPM.
MY QUESTION: Is their a conversion factor to plug in at the beginning of a CFM equation to compensate for vacuum on the intake side. ie: .0873(4"pipe) x 3700 fpm = 323 cfm This answer seems like it should be smaller using the same equation with blocked intake but it actually increases unless some allowance for the blocked intake is factored. ?
 
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  • #2
Are you talking about a partially or a completely blocked inlet; and, how and where are you measuring your velocity and where are you measuring your vacuum?
 
  • #3
The flow station was between the damper/closure and the fan on the intake side. The measurements increase as the rate of blockage increases from partial to near full. ie: increasing damper angle, then blocking intake. It is a lot of work to change things around to measure velocity on the exhaust side so I was wondering if there was a conversion that factored in the higher vacuum readings.
 
  • #4
If I'm understanding your post correctly, you should be using the velocity pressure in the velocity calculation. It's total pressure minus static pressure.
 
  • #5
What type of velocity measurement instrument are you using?
 

1. How does a blocked pipe increase air velocity?

When a pipe is blocked, the available space for air to flow through becomes more restricted. This restriction causes an increase in air pressure, leading to an increase in air velocity to try to equalize the pressure inside and outside of the pipe.

2. Is increased air velocity always a result of a blocked pipe?

No, increased air velocity can be caused by a variety of factors, such as the shape and size of the pipe, the amount of air being pushed through, and the presence of obstructions or bends in the pipe. A blocked pipe is just one potential cause of increased air velocity.

3. How does increased air velocity affect the performance of a system?

Increased air velocity can have both positive and negative effects on the performance of a system. On one hand, it can improve the efficiency of airflow and increase the speed at which air is delivered to its intended destination. However, it can also create turbulent flow and increase the risk of damage to the system or decrease its overall effectiveness.

4. Can a blocked pipe cause a decrease in air velocity?

Yes, a blocked pipe can cause a decrease in air velocity if the blockage is significant enough to restrict the flow of air. This decrease in air velocity can lead to a decrease in system performance and potentially cause other issues, such as increased energy consumption or decreased air quality.

5. How can a blocked pipe be prevented or fixed to maintain optimal air velocity?

Regular maintenance and cleaning of pipes can help prevent blockages from occurring. If a blockage does occur, it can often be removed by using a plumbing snake or other tools designed for clearing pipes. In some cases, it may be necessary to replace the pipe entirely to ensure optimal air velocity and system performance.

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