# Relationship between air pressure and flow rate

What is the relationship between pressure drop and flow rate (equation wanted)? the source, and the downstream destination pressure is usually atmospheric. is understanding the difference between flow, pressure, and velocity and knowing when Velocity refers to how fast the air is moving in distance per unit of time. This relationship can be explained using Bernoulli's principle. As back pressure increases, the volumetric flow rate of a blower decreases. Air pressure and flow are common terms in compressor systems, but what exactly with the proper air volume and flow rate so that no energy is wasted. Have questions about the relationship between pressure and flow?.

Total Pressure, Velocity Pressure, and Static Pressure It is convenient to calculate pressures in ducts using as a base an atmospheric pressure of zero. Airflow through a duct system creates three types of pressures: Each of these pressures can be measured. Air conveyed by a duct system imposes both static and dynamic velocity pressures on the duct's structure. The static pressure is responsible for much of the force on the duct walls. However, dynamic velocity pressure introduces a rapidly pulsating load.

Static pressure Static pressure is the measure of the potential energy of a unit of air in the particular cross section of a duct. Air pressure on the duct wall is considered static.

Imagine a fan blowing into a completely closed duct; it will create only static pressure because there is no air flow through the duct. A balloon blown up with air is a similar case in which there is only static pressure. Dynamic velocity pressure Dynamic pressure is the kinetic energy of a unit of air flow in an air stream. Dynamic pressure is a function of both air velocity and density: Obviously, there are pressure drops across the clean-up equipment dryers and filterswhich could equate to 10 to 15 psig or more.

But if the system was properly sized and maintained, this should be easily factored into what to set the discharge pressure of the compressor.

### Relationship between Flow Rate and Pressure | Physics Forums

Assuming that the clean-up equipment and piping distribution system were poorly sized and maintained, which equates to a psig pressure drop, you could still cut the pressure on the compressor operating at psig to psig, and still maintain the desired 75 psig on the production floor. Dialing the pressure down by 25 psig, the plant could save To calculate the energy savings, use the energy equation below: To calculate kW, multiply BHP by the constant.

Typically compressor manufacturers utilize a 1. Therefore, a hp rotary screw air compressor actually pulls on average BHP at full load, depending on the manufacturer. If the compressed air system was properly audited on the supply and demand side, which resulted in adding the proper amount of storage, pressure flow controller, etc.

Keep doing this over a period of time, and you will eventually have someone scream at you. Then turn it up 2 psig, and leave it alone. Another way to reduce leaks is to have a leak audit performed and implemented.

However, remember that you can effectively reduce leaks, but you can never completely eliminate them. For example, if the pipe size is reduced, the velocity will increase and act to decrease the static pressure.

If the flow area increases through an expansion or diffuser, the velocity will decrease and result in an increase in the static pressure.

If the pipe diameter is constant, the velocity will be constant and there will be no change in pressure due to a change in velocity.

## The Relationship Between Pressure and Flow in a Compressed Air System

As an example, if an expansion fitting increases a 4 inch schedule 40 pipe to a 6 inch schedule 40 pipe, the inside diameter increases from 4.

If the flow rate through the expansion is gpm, the velocity goes from 9. The change in static pressure across the expansion due to the change in velocity is: In other words, pressure has increased by almost 0. Pressure Change due to Head Loss Since head loss is a reduction in the total energy of the fluid, it represents a reduction in the capability of the fluid to do work.