Turbine flow meter: working principle, types, installation, and everything else
The turbine flow meter is one of the most accurate flow meters available, and as such, one of the most common in fiscal applications such as custody transfer for petroleum. Big money products need very accurate meters.
Even though you can find expensive digital turbine flow meters in fiscal applications, there are many cheap, mechanical alternatives for clean liquid applications.
A turbine flow meter has a fairly simple design, simple working principle, and straightforward installation and maintenance. I had a chance to work with turbine flow meters in a variety of applications in São Paulo. So let me introduce you to this nifty little machine. Stick with me, and find out how it works, and where to deploy it.
How does a turbine flow meter work?
The turbine flow meter has a relatively simple working principle compared to other flow meters on the market. Basically, the flow meter uses mechanical movement inside the meter to calculate the flow. Let’s break that down some more.
The turbine flow meter has a rotor with blades mounted on a bearing and supported inside the meter by a central shaft. When you have flow in the pipe, the kinetic energy of the product will make the rotor spin.
The blades are built from a paramagnetic material. So pickoffs, mounted externally without contact with the fluid, create a magnetic field in the pipe. Thus, when the blades pass through this field, they generate voltage proportional to the velocity of rotation, which can be used to calculate the flow rate.
The signal from the pickoffs can go into an external transmitter and convert to other types of communication. You can also use a preamplifier to read these pulses directly from the turbine flow meter without the transmitter.
Turbine flow meter measuring range and other specifications
Let’s talk about the turbine flow meter’s measuring range. Turbine flow meters don’t measure flow from zero. You need a minimum flow to get the rotor moving to create electrical pulses.
Usually, you can find turbines offering turndowns of 10:1. So you can apply this flow meter from small to big pipe sizes. You can also buy specific models to work in fiscal applications to measure liquid or gas flow.
However, the turbine flow meter does have one nemesis: viscosity change. Measurements can become inaccurate when the product gets thicker or tinner. However, you can find flow meters designed to work in low viscosity or high. But some experts recommend applying turbine flow meters below 30 centipoise (cP) to keep your flow meter’s linearity from decreasing.
Turbine flow meter installation
In many applications, the turbine flow meter works much like other meters as far as installation. I’ll talk about two examples, a process flow meter, and a fiscal flow meter.
The process flow meter, a straightforward device for liquid flow, has an accuracy of +-1 percent and can work in pipes from one-half to two national pipe threads (NPT). The manual recommends an inlet run of 10 times the pipe diameter and outlet run of five times the diameter.
The fiscal meter, on the other hand, has an accuracy of +-0.25 percent in pipes from 1 to 2.5 inches and +-0.15 percent from 3 to 24 inches. In small meter tubes, after the strainer, you need an inlet run of 20 times the diameter and outlet run of five. If you have two- or three-section meter tubes, after the strainer you need 10 times the diameter and five after the meter.
The best turbine flow meters on the market
Many vendors are offering turbine flow meters for gas or liquid flow measurement and for fiscal and process flow. We have a few examples here for your reference, but the market has many more.
BARTON Series 7400 turbine flow meter
Cameron, a Schlumburger company, also has different turbines for gas and liquid flow, plus a lot of experience in the fiscal realm. A few numbers on this device:
- Line sizes: 3/4 to 12 inches
- Fluid type: gas
- Linearity (standard): +-1.0% of reading overflow range
- Repeatability: ±0.2%
OMEGA Economical – FTB1300 Series turbine flow meter
OMEGA has a ton of devices online; I picked the Economical liquid turbine flow meter to use here as an example of pure turbine flow meter. Take a look at its data:
- Accuracy: ±1% of actual flow
- Pressure: up to 345 bar (5000 psi)
- Material: stainless steel
To know more about flow meters, please ask our engineers!
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