Dwyer Pitot Tube / Accutube Products
Pitot tube and orifice plate flow elements creates a differential pressure square root proportional to gas, liquid, or steam flow in a duct. Flow meters measure the flow of fluids and report the results in a volume per time or mass per time such as gallons per minute or Kg/min. Since fluid properties vary so much from corrosive, high temperature, gas, liquid to steam, so do flowmeter technologies and materials. Let’s focus on orifice plate and pitot tube technologies carried here at TEquipment.
Orifice Plates
An orifice plates are inserted between flanges into round ducts to measure gas or steam flows. They are a thin metal, usually stainless, with a hole in the center. The resulting pressure drop as gas flows past is measured by differential pressure sensors with taps on either side of the plate in the duct. They are low cost and maintenance free, but have some limitations.
Application considerations/limitations of Orifice Plates
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Low turndown (i.e. the range from max to min flow is limited compared to other technologies)
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High pressure drop/losses to overcome
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Low accuracy
Pitot Tube
A pitot tube flow elements, like an orifice plate, creates a differential pressure square root proportional to gas, liquid, or steam flow in a duct. Chief advantages over other flow elements include relatively low purchase price, low installation cost, and low permanent pressure loss (equates to low operating costs). A pitot consists of a pipe with holes across its length inserted into the cross section of the duct. At the connection point there is a fitting on duct or pipe and mating fitting on the pitot tube. Turndown is better than an orifice plate and there is less pressure drop to overcome.
Accutube
![meriam_accutube]()
An accutube is a true double-averaging type of pitot tube manufactured exclusively by Meriam. These tubes use a round probe design that has been used for decades, unlike new Bullet or Diamond designs. The good thing about this is that round probe is low-cost and has been proven effective over many years of use. Meriam Accutubes boast up to ±0.5% accuracy when factory calibrated
and better than ±1% uncalibrated. These tubes also feature high flow turndown of 10:1. These relatively inexpensive tubes are the best option when it comes to capability, reliability, and longevity.
Other benefits of Meriam Accutubes:
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Very low permanent pressure loss
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No moving parts = more stable and accurate over time
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Multiple mounting options (wet tap, insertion, flanged, inline)
Flow Meter Selection Questions
Knowing as much as possible about your application will help in selecting the right technology and specific flow meter model.
1. Flowing gas data
a. Flow rate in desired units
b. Base conditions
i. Pressure
ii. Temperature
c. Flowing conditions
i. Pressure
ii. Temperature
iii. Viscosity at flowing temperature
d. Differential at maximum flow
e. Specific gravity
f. Flowing gas or liquid
2. Readout instrument
3. Description of installation configuration
4. Line size
5. Line Material
6. Accuracy required