Turbine flow meters – what you need to know
What’s a turbine flow meter? We’ve covered most of the flow meters you’ll see on the market, but not this one – until now.
What’s a turbine flow meter?
We’ve covered most of the flow meters you’ll see on the market, but not this one – until now. Today, we’ll discuss one of the most accurate flow meters out there, and as such one of the most common in fiscal applications such as custody transfer for petroleum. Big-money products need super-accurate meters, you know?
But even though you can find expensive turbine meters in fiscal applications, you’ll also find cheaper versions in clean liquid processes. And you’ll usually find these meters in the “mechanical” category on the market. Some vendors have spiels all set to convince you to buy a fancier digital meter, but decide for yourself.
A turbine flow meter has a fairly simple design, easy-to-grasp principle, and straightforward installation and maintenance. I had a chance to work with turbines in a variety of applications in São Paulo. So let me introduce you to this nifty little machine.
Stick with me, and let’s find out where to deploy it.
The meter has a dead-simple working principle compared to other meters on the market. Basically, the flow meter translates 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 with 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 flow rate. And that makes the flow rate proportional to the velocity of the rotor rotation. Simple as that!
The signal from the pickoffs can go into an external transmitter and convert to other types of communication. However, you can also use a preamplifier to read these pulses directly from the turbine flow meter without the transmitter.
Let’s talk about range. Now, turbine flow meters don’t measure flow from zero. You need a minimum flow to get the rotor moving to create the 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. It doesn’t like it when the product gets thicker or thinner. Still, 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.
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 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.
On the market, you have tons of vendors 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. Check out Visaya’s device page for some of that. And don’t forget to check the support in your region and other such important stuff.
Daniel Series 1500
Daniel, an Emerson automation company, has many types of turbine flow meters, but all of them focus on fiscal applications. Some deets on this line:
- Line size range: DN25 to DN600 (1 to 24 inches)
- Fluid type: liquid
- Linearity (standard): ±0.25% for 1 to 2.5 inches; ±0.15% for 3 to 24 inches
- Repeatability: ±0.02%
- Process temperature range (standard)
- Carbon steel: -29 to +60°C (-20 to +140°F)
- Stainless steel: -40 to +60°C (-40 to +140°F)
You can read more about the Daniel Series 1500 here.
BARTON Series 7400
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%
You can read more about the BARTON Series 7400 here.
OMEGA Economical – FTB1300 Series
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
You can read more about the economical liquid turbine flow meter here.
This video shows a turbine flow meter installed in a gas metering system: