Differential Pressure Flow Meter or DP Flow Meter is the most common flow meter. The vast amount of experience (measurement techniques have been around for 100 years) is reflected in the large number of appearances. Differential pressure flow gauges measure volume flow in gases, liquids, and vapors.
Definition of Differential Pressure Flow Meter
Differential Pressure Flow Meter is a type of flow meter that uses the most basic flow principle, namely the existence of a flow due to pressure differences from two specific areas. In accordance with Bernauli’s law is described as a difference in pressure that can cause flow velocity.
By using certain equipment, where the flow of fluid to the pipe is guided to several parts of the equipment that have different areas causing variations in flow velocity and flow pressure. and flow pressure. By measuring the value of pressure changes, it can be calculated the velocity flow of the fluid.
There are many types and forms that can give rise to differential pressure flow meters applied in industry in accordance with the law of bernouli equation:
- Orifice Plate
- Venturi Tube:
- Flow Nozzle:
- Cones Meters
- Wedge Meters
- Pitot Tube
Working Principle of Differential Pressure Flow Meter
Previously it has been mentioned that this DP Flow Meter uses bernoulli law to measure fluid flow in pipes. Differential pressure flow gauges cause a narrowing in the pipe that creates a decrease in pressure across the flow gauge.
As the flow increases, more pressure drops are created. Impulse piping directs the upstream and downstream pressures of the flowmeter to a transmitter that measures differential pressure to determine fluid flow. This technology accounts for about 21% of the world market for flowmeters.
Also Read: Understanding and Function of Flow Meter
Bernoulli’s equation states that the decrease in pressure across the narrowing is proportional to the square of the flow rate. Using this relationship, 10 percent of full-scale streams produce only 1 percent of full-scale differential pressure. At 10 percent full-scale flow, the accuracy of the differential pressure flow gauge depends on the accuracy of the transmitter in the 100:1 differential pressure range.
Differential pressure transmitter accuracy usually decreases at low differential pressures within its range, so flowmeter accuracy can be lowered in the same way. Therefore, this non-linear relationship can have a detrimental effect on the accuracy and decrease of differential pressure flow gauges. Keep in mind that what is interesting is the accuracy of the flow measurement system — not the accuracy of the differential pressure transmitter.
Different geometries are used for different measurements, including orifice plates, flow nozzles, laminar flow elements, low-loss flow tubes, segmental wedges, V cones, and Venturi tubes.
Advantages and Disadvantages of DP Flow Meter
The advantage of this technology is the low cost, multiple versions can be optimized for different liquids and purposes, approved for prisoner transfer (although it is increasingly rarely used for this), it is a well-understood way to measure flow, and it can be paired with a temperature/pressure sensor to provide mass flow for steam and other gases. The downside is that the range is not good due to non-linear differential pressure signals (excluded laminar flow elements), accuracy is not the best and can deteriorate with wear and blockage.
How to use it?
Differential Pressure Flow Meter inferentially measures the flow of liquids, gases and vapors, such as water, cryogenic fluids, chemicals, air, industrial gases, and vapors. Be careful using differential pressure flow gauges for liquids with high viscosity, such as some hydrocarbons and foods, as their accuracy can decrease when reynolds numbers are low.
This flow meter can be applied to relatively clean liquids. With proper attention to construction materials, the flow of corrosive liquids, such as those found in the chemical industry, can be measured.
A rather dirty liquid can be measured by cleaning the impulse pipe with an inert liquid. Be careful when using differential pressure flow gauges in dirty services because dirt can clog impulse pipes and cause incorrect measurements. Diaphragm seals can sometimes be applied in this application. But it should be remembered that the diaphragm seal can decrease the performance of the differential pressure emitting system, and therefore, decrease the performance of the flow measurement system.
Differential pressure flow meters generally apply to many streams in most industries, such as mining, mineral processing, pulp and paper, petroleum, chemical, petrochemical, water, and wastewater industries. Other flow measurement technologies may perform better than differential pressure flow meters in many applications, but differential pressure flow meters are still widely used due to longstanding user familiarity with the technology.
Industrial Use
In its classification, DP Flow Meters are used in oil and gas, chemical, electrical, water and waste, pharmaceutical, metal and mining, pulp and paper, food and beverage and HVAC.
Differential Pressure Flow Meter Application
Due to the non-linear relationship between flow and differential pressure, the accuracy of flow measurements at the bottom of the flow range can be derived. Inserting impulse pipes can be a concern for many services. For slurry services, cleaning should be used to keep impulse pipes from getting clogged.
For fluid service, the impulse pipe must be oriented and tilted so that it remains full of fluid and does not collect gas. For gas service, the impulse pipe must be oriented and tilted so that it remains full of gas and does not collect liquid. In steam service, steam is allowed to condense in some impulse pipes to form a liquid seal between the hot steam and the transmitter to protect the transmitter from heat.
Be careful because differential pressure transmitter calibration can be affected by the accumulation of fluids or gases in impulse tubes. In addition, the accuracy of the flow measurement system may decrease when varying amounts of fluid can accumulate during operation.
Also Read: Calibration Types on Flow Meters
Calibration issues can be critical to the successful application of this technology. For example, the release of differential pressure transmitters for calibration exposes the transmitter to various sources of potential problems that can affect the measurement, not the least of which is the extent to which the transmitter tube is tightened back after calibration. Calibration should generally be done in-situ whenever possible and the provision to do so must be addressed during the design phase. For example, differential pressure transmitters can be purchased with integral valve manifolds that allow easy calibration without disconnecting the impulse tube.
Gas applications should be carefully designed because changes in operating pressure and operating temperature can dramatically affect flow measurements. In other words, the density of the gas can vary significantly during operation. As a result, the differential pressure generated by the flowmeter can also vary significantly during operation. Failure to compensate for this effect can lead to flow measurement errors of 20 percent or more across many applications. In this application, a flow computer can be used to calculate corrected flow measurements using actual pressure, temperature, and flow measurements.
Read Next: Differential Pressure Flow Meter
Hopefully the article “Differential Pressure Flow Meter: Understanding, How It Works, and Applications” can answer questions for readers, and can help expand the knowledge of its readers, hopefully useful!