Can I determine pressure loss by only using cfm & psi at 2 locations?

In summary, the consultant wants to install gauges in various locations to measure cfm and psi. These gauges are supposed to help determine pressure loss in the system. However, this is not a foolproof method and should only be used after the system has been analyzed by a qualified engineer.
  • #1
reedcj1
2
0
I work for a manufacturing company. We want to make some improvements to our compressed air system, but we want to establish a baseline of our current efficiency for cost justifications, etc. One planned improvement, is redesigning our current piping layout. We spoke with a consultant who wants to sell us several gauges to measure cfm and psi at various locations in the facility. He claims by measuring cfm and psi at the header nearest compressor, we will be able to determine pressure loss from header to point of usage. Is this possible or is he just trying to sell product? Are there not other variables that need to be considered (ie: temperature, distance in pipe, number of fittings, types of fittings, pipe diameters, etc.) ? I realize we only need ballpark figures for justification, but can we measure pressure loss by only knowing cfm and psi at two given locations?
 
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  • #2
If you can't measure pressure loss with two pressure gauges, it's time to start over.
 
  • #3
I’m sorry, I am not an engineer and know little about fluid dynamics, so I am having trouble with this. We are trying to determine pressure loss due to the facilities current piping layout (ie: undersized pipe diameter, multiple fittings, switchbacks, etc.) Let’s say I place gauge at a 4” compressor header (Gauge 1), and a gauge on a 1” line 300ft downstream (Gauge 2) at point of usage (sandblaster). Assuming we are at steady state, static pressure at Gauge 1 and Gauge 2 should be equal. Now if I start the sandblaster I will exhaust the compressed air through a 1” line at Gauge 2, and create a transient system. Is it as simple as taking pressure at Gauge 1 minus pressure at Gauge 2 to determine Pressure Loss? Pressure Loss = Total Pressure1 – Total Pressure2. Are there gauges that measure total pressure? Total Pressure = Dynamic Pressure + Static Pressure.
 
  • #4
If you are using compressed air in your system, the friction produced by the flow of the air thru fittings, valves, lengths of pipe, etc., will produce pressure drops in the system. Allowing the pressure to exit thru a sand blaster will create a temporary transient for a brief period after opening the valve, but any transient effects should die out after a certain interval.

I don't know how complicated your system is, and I don't know the qualifications of your consultant. If you want to improve your current piping layout, then the current layout should be analyzed by a qualified engineer. IMO, the engineer will provide his own tools, gauges, whatever is necessary for him to do his job. I would recommend that your management and the engineer understand beforehand what the engineer will do, what results he is to furnish, and what additional equipment or information he requires before the project commences.
 
  • #5
The dynamic pressure is related to the volumetic flow rate - ie cfm.

You can pre-analyze your system with some charts.

http://www.engineeringtoolbox.com/horsepower-compressed-air-d_1363.html
as it says add 10 to 15% fro friction of the air compressor

http://www.engineeringtoolbox.com/compressed-air-pressure-loss-d_1014.html
for a pressure loss in pipe. For each reduction or elbow, I think you add about 10 feet of straight pipe but I am not sure of that figure.

http://www.engineeringtoolbox.com/air-line-length-recommended-sizes-d_1537.html
for recommended sizes of pipe.

( right now the site is slow for some reason - just wait it out )
 

1. What is pressure loss?

Pressure loss refers to the decrease in pressure that occurs as a fluid flows through a pipe or other conduit. It is typically caused by friction between the fluid and the walls of the conduit, as well as other factors such as changes in elevation or flow rate.

2. Can pressure loss be determined by only using cfm and psi at 2 locations?

In most cases, no. Pressure loss is a complex phenomenon that is affected by many factors, including the size and shape of the conduit, the properties of the fluid, and the flow rate. While cfm (cubic feet per minute) and psi (pounds per square inch) can provide some information about pressure loss, they are not sufficient on their own to accurately determine it.

3. What other factors should be considered when determining pressure loss?

Other factors that should be taken into account when determining pressure loss include the length and diameter of the conduit, the roughness of the walls, and the viscosity of the fluid. Additionally, the type of fluid being transported and any changes in elevation along the conduit should also be considered.

4. Can pressure loss be calculated using mathematical equations?

Yes, there are various mathematical equations and models that can be used to calculate pressure loss. These equations take into account the aforementioned factors and can provide a more accurate estimation of pressure loss compared to using only cfm and psi at 2 locations.

5. Why is it important to determine pressure loss?

Determining pressure loss is important for various reasons. It can help engineers and scientists design more efficient and cost-effective piping systems, as well as identify potential issues or inefficiencies in existing systems. Additionally, understanding pressure loss can help ensure the safe and effective transport of fluids in various industries such as oil and gas, water treatment, and HVAC systems.

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