Differential Pressure Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Feb 03, 2022

The differential pressure calculator will assist you in computing the change in pressure across a valve or a fluid flow device in a fluid system. From a pitot tube in an aircraft to measure airspeed to a pneumatic valve in a robotic arm, and all things in between, differential pressure in a fluid flow system play a vital role in their operations.

Pressure switches act on the pre-set values of change in pressure to trigger circuit breaking or make any other adjustments like opening an extra valve, redirecting the fluid flow, or detecting a blockage in the pipes or airways. Such pressure switches operate along with pressure sensors or gauges that monitor the pressure in a fluid system.

The concept is useful for fluid flows in a pipe regardless of the pipe's location. It could be a respiratory medical device, flow measurement in aircraft, heating, ventilation, air conditioning(HVAC) systems, or any other hydraulic or pneumatically operating system. The pressure differential is a function of discharge, flow coefficient, and the specific gravity of the fluid.

This article will explain differential pressure and how to calculate flow rate using differential pressure.

What is differential pressure?

Consider fluid flow through an orifice, a venturi, or a similar constriction having a pressure gauge on either side. The change in pressure between the two gauges is known as differential pressure. It is helpful to find any blockages or leaks in the system as it will cause a change in differential pressure. Mathematically, it is related to the flow factor or flow coefficient, volumetric flow rate, and the fluid's specific gravity:

Kv=QSΔPΔP=Q2Kv2S\quad \begin{align*} K_v &= Q\sqrt{\frac{S}{\Delta P}} \\\\ \Delta P &= \frac{Q^2}{K_v^2} S \end{align*}

where:

  • KvK_v – Flow factor;
  • SS – Specific gravity of the fluid;
  • QQ – Volumetric flow rate; and
  • ΔP \Delta P – Differential pressure.

The flow factor is the efficiency of the fluid flow through a pipeline. It is also expressed in m3/hr\text{m}^3/\text{hr}.

Differential pressure calculation – Calculate flow rate from pressure differential

To calculate differential pressure:

  1. Enter the specific gravity of the fluid or select from the list of fluids.
  2. Fill in the volumetric flow rate for the flow.
  3. Insert the flow factor.
  4. The calculator will return the differential pressure.

To calculate the flow rate, you can leave the field empty and enter the pressure difference instead.

Example: Using the differential pressure calculator

Find the pressure difference if the water has a volumetric flow rate of 10 l/min and a flow factor of 5 l/min.

To calculate differential pressure:

  1. Enter the specific gravity of water as 1.
  2. Fill in the volumetric flow rate for the flow as 10 l/min10 \text{ l/min}.
  3. Insert the flow factor as 5 l/min5 \text{ l/min}.
  4. Using the differential pressure formula:
ΔP=Q2Kv2S=10252×1=4 bar\qquad \scriptsize \Delta P = \frac{Q^2}{K_v^2} S = \frac{10^2}{5^2}\times 1 = 4 \text{ bar}

FAQ

What do you mean by differential pressure?

The change in pressure when a fluid passes through a constriction like a venturi or an orifice is the differential pressure. It has the same units as pressure, i.e., bars or Pa. It is a pressure measurement method and is very common in fluid flow systems.

How do you calculate differential pressure?

To calculate differential pressure:

  1. Find the square of volumetric flow rate.
  2. Find the square of flow factor.
  3. Divide the square of volumetric flow rate by the square of flow factor.
  4. Multiply the resultant with the specific gravity of the fluid to obtain the differential pressure.

How do I calculate flow rate using differential pressure?

To calculate flow rate using differential pressure:

  1. Divide the pressure difference (ΔP) by the specific gravity (S) of the fluid.
  2. Find the square root of the resultant division.
  3. Multiply the root by the flow factor (Kv) to obtain the flow rate (Q) for the fluid system. Mathematically, that's:
    Q = √(Kv × (ΔP/S))

What are the applications of differential pressure?

The differential pressure is a measurement method that is used in:

  • Detecting blockages and leaks in the system;
  • Activating pressure switches and valves;
  • Determining the proper functioning of fluid flow systems;
  • Measuring liquid levels and flow rates; and
  • Respiratory flow in medical devices.
Rahul Dhari
Fluid properties
Fluid
Water
Specific gravity
Flow properties
Discharge or volumetric flow rate
ft³/h
Flow factor
ft³/h
Result
Differential pressure
psi
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