Differential Pressure
Calculate differential pressure across a valve using ΔP=(Q²/Kv²)×S. Free fluid dynamics tool with bar, Pa, psi, breakdowns, and charts for HVAC engineers.
About This Calculator
The Differential Pressure Calculator is a free online tool for engineers, technicians, and students to compute the pressure drop across valves, orifices, venturis, and other fluid flow constrictions. It uses the standard fluid dynamics formula ΔP = (Q² / Kv²) × S, where Q is the volumetric flow rate, Kv is the flow factor, and S is the specific gravity of the fluid.
Differential pressure measurement is fundamental in fluid mechanics and industrial process control. It is used in HVAC systems to monitor filter cleanliness, in medical ventilators to track airway pressure, in aircraft pitot-static systems to measure airspeed, and in chemical plants to detect pipeline blockages. Our calculator supports 13 common fluids including water, ammonia, oils, mercury, and milk, or you can enter a custom specific gravity for any other fluid.
How the Formula Works
The flow factor Kv represents the efficiency of a valve or constriction — it is defined as the volume of water (at 15.6 °C) in L/min that creates a 1 bar pressure drop across the device. The pressure drop increases with the square of the flow rate and decreases with the square of the flow factor. Higher specific gravity fluids (like mercury at 13.55) produce proportionally larger pressure drops for the same flow conditions.
Regional Notes
IN: Differential pressure gauges in Indian process industries typically use bar or kg/cm² units. Our calculator provides results in bar, Pa, and psi for broad compatibility.
US: US engineers commonly use psi (pounds per square inch) for pressure measurements in hydraulics, pneumatics, and HVAC applications. The results section includes psi values for convenience.
UK: UK industries use a mix of bar and Pa depending on the sector — bar is common in hydraulics while Pa is standard in building services and ventilation. All units are provided.
Frequently Asked Questions
What is differential pressure?
Differential pressure (ΔP) is the change in pressure when a fluid passes through a constriction like a valve, venturi, or orifice. It is measured using two pressure gauges placed on either side of the constriction and is commonly used to detect blockages, leaks, and measure flow rate in fluid systems.
How do you calculate differential pressure?
Differential pressure is calculated using the formula ΔP = (Q² / Kv²) × S, where Q is the volumetric flow rate, Kv is the flow factor (a measure of the valve or constriction's efficiency), and S is the specific gravity of the fluid. The result is in bar.
What is the flow factor Kv?
The flow factor Kv is a measure of the efficiency of fluid flow through a pipeline, valve, or constriction. It is expressed in L/min and represents the volume of water at 15.6°C that creates a 1 bar pressure drop across the device. Higher Kv values indicate less resistance to flow.
What units are used for differential pressure?
Differential pressure can be expressed in multiple units including bar, Pascal (Pa), and pounds per square inch (psi). 1 bar equals 100,000 Pa and approximately 14.5038 psi. Our calculator provides results in all three units for your convenience.
What are the applications of differential pressure measurement?
Differential pressure measurement is widely used in HVAC systems for airflow monitoring, medical respiratory devices, industrial process control for detecting filter blockages, aircraft airspeed measurement using pitot tubes, liquid level measurement in tanks, and flow measurement across orifices and venturis.
How do I use this differential pressure calculator?
Select a fluid from the dropdown menu (or enter a custom specific gravity), enter the volumetric flow rate in L/min, and enter the flow factor Kv in L/min. Click 'Calculate Differential Pressure' to get the pressure drop in bar, Pa, and psi with breakdowns and charts.
Can I calculate flow rate from differential pressure?
Yes, the formula can be rearranged as Q = Kv × √(ΔP / S). To calculate flow rate, enter the pressure difference and flow factor, then the calculator will determine the corresponding volumetric flow rate.
What is specific gravity and how does it affect differential pressure?
Specific gravity (S) is the ratio of a fluid's density to the density of water at 15.6°C. Fluids with higher specific gravity, like mercury (13.55), produce larger differential pressures for the same flow rate and flow factor compared to lighter fluids like gasoline (0.72) or water (1.0).