At Mid-West Instrument, we manufacture differential pressure gauges designed to measure the difference between two pressure points in a system. To gather these readings, the system must be equipped with properly installed pressure taps. These taps act as access points for fluid pressure to be transmitted to a measurement device. Understanding how pressure taps work—and how they are positioned—is essential to ensuring accurate and reliable differential pressure readings.
Pressure Tap Function and Design
Pressure taps are small openings in a pipeline, tank, or other pressurized system. They are installed specifically to allow internal fluid pressure to reach the sensing elements of a differential pressure gauge or transmitter. In differential pressure applications, two taps are always used: one for the high-pressure side and one for the low-pressure side. These taps connect to the gauge via tubing or impulse lines, transmitting the pressure from each side of the process. The gauge then measures the difference between these two pressures and displays it.
The internal pressure of the fluid at each tap exerts force through the connecting lines, applying it directly to the sensing mechanism of the differential pressure instrument. This can be a diaphragm, bellows, or piston, depending on the specific gauge model. Once the pressure from both taps reaches the instrument, the difference is measured and converted into a readable value, either analog or digital, depending on the gauge configuration.
Importance of Proper Placement
To get a representative pressure reading, pressure taps must be installed in precise and well-planned locations. Their placement depends on what is being measured and the dynamics of the system. In flow measurement applications, pressure taps are typically placed on either side of a primary flow element such as an orifice plate, venturi, or flow nozzle. This setup allows for the measurement of the pressure drop created by the flow restriction, which can then be used to calculate flow rate.
In filtration systems, pressure taps are installed upstream and downstream of a filter. This configuration lets the user monitor the pressure differential across the filter element, helping to determine when a filter is clogged or needs replacement. For accuracy, taps must be positioned in locations where flow is stable and not affected by turbulence, elbows, or nearby valves. Misplaced taps can introduce measurement errors by picking up pressure anomalies or flow disturbances that do not represent the actual system conditions.
Pressure Tap Configuration and Types
There are several standard configurations for pressure taps, and each is suited for different types of installations. Common configurations include corner taps, flange taps, and pipe taps. Corner taps are located immediately upstream and downstream of an orifice plate. Flange taps are positioned one inch upstream and one inch downstream from the plate, typically drilled through the flanges holding the orifice. Pipe taps are located further away from the flow element and are drilled directly into the pipe wall.
The choice of tap configuration depends on process requirements, accuracy needs, and industry standards. Each configuration impacts the pressure profile at the tap location and therefore affects the resulting differential pressure measurement.
Connection and Transmission to the Gauge
Once the pressure taps are installed, they are connected to the differential pressure gauge using tubing or impulse lines. These lines carry the pressure from the tap to the high and low sides of the gauge. To maintain accuracy, it’s important that these lines are free of leaks, properly supported, and as equal in length as possible to avoid introducing measurement error due to line losses or unequal response times. In some installations, the lines may also be filled with compatible fluid to ensure consistent transmission, particularly in systems using remote or elevated mounting.
Conclusion
Accurate differential pressure readings depend on properly installed and maintained pressure taps. At Mid-West Instrument, we emphasize the importance of correct tap placement, proper configuration, and secure connections to ensure that pressure data is representative and reliable. Pressure taps are essential components of any differential pressure measurement system and directly influence the performance and accuracy of the instruments connected to them.
For over 60 years, Mid-West Instrument has been a leading provider of premium differential pressure gauges. Need help finding the right pressure gauge and equipment for your business? Reach out to us today to speak with one of our experienced professionals.