Backpressure and Hose Length in non-exhaust application.

In summary, the conversation discusses the need for a back-pressure system to simulate field use of a mechanic's machines in their shop. They use blowers and hoses of varying lengths and need to determine the back pressure for optimal material usage. The conversation also touches on the relationship between PSI and CFM in regards to blower selection and hose size and length. The mechanic mentions not fully understanding the engineering and physics behind this and expresses gratitude for any assistance.
  • #1
Joseph West
1
0
Hello,

First, thank you for any assistance. I am a mechanic and my Super want's me to design a back-pressure system that will simulate field use of my machines in my shop. We spray several types of fireproofing thru hose's that vary in length between 50 and 500 feet.

We use blower's that put out 15-20 psig and 300-25,000cfm.

I was told by the material manufacturer that the back pressure on a 50' hose with the optimum material in it should be between 3.5-4 PSIG but I can't seem to figure out how to relate that to a longer hose or if 3.5-4 PSIG of back pressure is (or can be considered) a lot of air pressure.

Can you have 5 PSIG with a 15,000 CFM? How does that work.

I am sorry I am not an engineer or physics specialist so much of this I just don't understand so any help is truly appreciated.

Joseph L. West
 
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  • #2
The resistance of movement of fluid in your hose dictates what pressure the blower will output. From the pump you will have pressure P and at the hose end you will have Patm = 0 pressure guage. Along the length of the hose, the pressure is a function of distance from the pump. If the hose is length L, then at the pump there is pressure P, one quarter the way down, the pressure is (3/4)L, all the way to the end where P=0, assuming you do not have many twists, turns and elbows of sorts.

Size and length of hose matters. Longer hoses have more pressure drop ( back pressure ). Smaller diameter hoses have more pressure drop.

To relate PSI and CFM of the blower, you have to look at the manufactuere's fan curve for your particular blower (and rpm). It should translate that if the blower is producing more PSI then it is outputting less CFM( ie longer or smaller hose), less PSI means more CFM (shorter or larger diameter hose).

Can you have 5 PSIG with a 15,000 CFM? How does that work.
Sure, why not. Depends on your blower selection and hose size and length.
 

1. What is backpressure in a non-exhaust application?

Backpressure refers to the resistance or force that opposes the flow of a fluid, such as air or water, through a system. In a non-exhaust application, backpressure can occur when a fluid is pushed through a hose, causing resistance and pressure build-up.

2. How does backpressure affect the performance of a non-exhaust application?

Backpressure can significantly impact the performance of a non-exhaust application. It can reduce the flow rate of the fluid, decrease the efficiency of the system, and potentially damage components due to increased strain and pressure.

3. How is backpressure measured in a non-exhaust application?

Backpressure is typically measured in pounds per square inch (psi) or kilopascals (kPa). This is done by using a pressure gauge at various points along the system to determine the pressure at specific locations.

4. What role does hose length play in backpressure in a non-exhaust application?

Hose length can have a significant impact on backpressure in a non-exhaust application. The longer the hose, the more resistance and pressure build-up there will be, resulting in higher backpressure. It is essential to consider the length of the hose when designing a system to avoid potential issues.

5. How can backpressure and hose length be managed in a non-exhaust application?

To manage backpressure and hose length in a non-exhaust application, it is crucial to choose the right size and type of hose for the system. Additionally, implementing proper fluid flow control and regular maintenance can help minimize backpressure and maintain optimal performance.

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