Relation between flow and pressure

How do Flow and Pressure Relate to One Another?

People who operate hydraulic equipment frequently make careless adjustments to hydraulic circuits, which can severely compromise the integrity of the equipment or even lead to catastrophes with tragic human consequences. As such, it is helpful to provide specific formulas and information for reference while adjusting hydraulic circuits.

When the pressure in a pipe increases, does the flow rate also increase? Does the diameter of the pipe matter when calculating the flow rate? Qualitative investigation suggests a proportionate link between pipe pressure and flow rate. This means that the relationship between stress and flow rate is linear. It is multiplying the velocity by the cross-section yields the flow rate. Assume a pipeline with a single pressure source at one end. The amount of Water flow meter that shoots out of a faucet depends on the pressure in the pipe. The closure of the valve prevents any flow from the tube.

Flow Rate, Pressure, and Pipe Diameter

The term “pipe diameter” is used to describe a pipe’s overall size when the wall thickness of the line is small enough that the outer and inner diameters are nearly identical. When referring to a tube made of a synthetic substance or metal, the diameter is often calculated as the mean size of the inner and outer diameters. DN is a unit of measurement based on the metric system (mm) (metric units). The pressure inside a pipe is the force exerted by the fluid inside.

Relation Between Flow and Pressure

First, the formula for calculating the flow rate is: flow rate = flow rate x pipe (ID) x tube (ID) x π ÷ 4. Thus, knowing one’s flow rate can help one determine the other.

Is it possible to estimate the flow rate if one only knows the pipe’s internal pressure P and diameter D?

There currently needs to be a reliable means to measure the speed or volume of the fluid in the pipe.

You make up a scenario in which the final piece of the pipe is a shutoff. The line is entirely devoid of any current. The internal pressure of a sealed tube always remains at a fixed value, P.

Accordingly, the pressure inside the pipe has no bearing on the flow rate; instead, the pressure drop gradient along the tube does. To determine the pressure difference at each end of the pipe, the pipe length and flow rate must be known.

Let’s pretend we take a qualitative analysis of the scenario. Pipe pressure and flow rate are proportional to one another. This means that the relationship between stress and flow rate is linear. It is multiplying the velocity by the cross-section yields the flow rate.

Only one end of the pipe is pressurized at any given time. Said the flow is one-way. When the pressure relief valve is closed, liquid cannot leave the tube in that direction upon activation of the switch. When the pipe pressure is high enough, it flows.

Experiments using hydraulic models allow for quantitative analysis. Put in a pressure gauge, meter the flow rate, or calculate the throughput. It is also possible to determine the flow rate in a pressurized pipe. A breakdown of the procedures used to arrive at your final answer follows.

It is required of you that you calculate the specific resistance of pipe S. In the case of corroded steel or iron pipelines. The Severe formula for determining the resistivity of a pipe is s=0.001736/d^5.3 or s=10.3n2/d^5.33.

Find the pressure differential at each end of the pipe using the formula H = P/(g)

Hence, H=P/(g+h)


H: in meters

P: Pressure difference between pipe ends 

P in Pa

Using the formula Q = (H/sL)^(1/2), you can determine the volumetric flow rate.

Calculating the velocity V = 4Q/(3.1416 * d^2)


Q = the quantity being measured

H = the vertical distance in meters between the pipe’s origin and its termination.

L = total length of the pipe in millimeters.

Calculating flow and pressure

Daniel Bernoulli initially introduced the concept of low-velocity high-pressure in a stream in 1726. A low-pressure situation occurs when the velocity is high. That’s what Bernoulli’s principle is all about.

Before developing the continuous medium theory in fluid mechanics, this was the guiding concept of hydrodynamics. The fundamental principle is the principle of energy conservation in fluid mechanics. That is, the sum of the energies of motion, gravity, and pressure remains unchanged.

As a result, it can only be used with perfect fluids with an infinite density and zero viscosity.

The following is a common statement of Bernoulli’s principle.


Bernoulli’s equation describes this phenomenon.


p is fluid pressure.

v is the fluid’s flow velocity.

ρ is the fluid density.

g is gravity.

h is the point’s height.

C is constant.

What are the pressure drop and the flow rate?

Technically and economically, the pressure drop (or pressure loss) indicates how much power the gadget needs to operate. Total fluid differential pressure between the device’s inlet and outlet is the unit of measure. Essentially, it indicates the amount of mechanical energy the fluid expands as it travels through the dust removal system (or other devices). Power Plant consumption of the respirator has a direct correlation.

This total considers the pressure drop along the route and the pressure decrease at the target site.

The pressure loss experienced by the fluid as it moves through a straight conduit is known as the along-range pressure drop.

The term “local pressure drop” describes the loss of pressure due to alterations to the flow cross-section as the liquid passes through a valve opening, an elbow, or some other local resistance.

The fluid is an exception to the regional norm. It spins continuously. Intensify the rubbing together of liquid molecules or the collision of individual particles. Dead water or a vortex flow meter area forms when liquid flows through a local device, and local pressure drops happen. Create a spot of wasted energy.

It adds unnecessary resistance and drains energy. Significant and abrupt shifts in the flow’s direction occur as the liquid passes through the local device. Additionally, the pattern of velocity distribution throughout the various segments is dynamic.

Flow and Differential Pressure?

The pipe flow rate is proportional to the pressure differential’s square root in sizing a system. With a more significant pressure difference, the flow rate increases. A pressure-regulating valve exists in the piping system (artificial pressure loss). The adequate differential pressure and flow rate both decrease. The pipeline pressure loss will be reduced as a result.

How to Determine the Flow Rate Using Only Differential Pressure?

The concept of fluids exchanging mechanical energy with one another underpins the differential pressure flowmeter’s measurement method.

Both dynamic and static pressure energy is present in the fluid moving through the horizontal pipe.

The conversion between these two kinds of energy under specific conditions unaffected the total energy.

Consider the equation for volume flow as an illustration.

Quantum kinetic energy Q v = CεA/sqr(2ΔP/(1 – β^4)/ρ1)

A higher level of compensation for temperature and pressure is needed to meet the compensation standards. It is assumed in the calculation book that all process parameters will be at 50 degrees. The flow rate can be determined at any given temperature and pressure. In reality, density conversion is the most crucial step.

Following is the breakdown of the computation.

Q = @sqr(ΔP/ρ) Nm3/h 0C101.325kPa*0.004714187 d^2 ε

This demonstrates the volumetric flow rate at standard atmospheric pressure and sea level.

Following the formula for density.

ρ= P T50/(P50 T)* ρ50

Where ρ, P, and T are values for temperatures and pressures.

The process reference point is indicated at 50 degrees gauge pressure by the numerical values ρ50, P50, and T50. The program allows you to combine these two formulas into a single one.

Leave a Comment

Your email address will not be published. Required fields are marked *