Industrial Turbine Flowmeters
Turbine flowmeter is an accurate and reliable flowmeter for both liquids and gases.
Turbine flowmeter consists of a rotor mounted at right angles to the flow and suspended in the fluid stream on a free-running bearing. The diameter of the rotor is very close to the inside diameter of the metering chamber, and its speed of rotation is proportional to the volumetric flow rate. Turbine rotation can be detected by solid state devices (reluctance, inductance, capacitive and Hall-effect pick-ups).
- In the reluctance pick-up, the coil is a permanent magnet and the turbine blades are made of a material that is attracted to magnets. As each blade passes the coil, a voltage is generated. Each pulse represents a discrete volume of liquid and the number of pulses per unit volume is called the meter’s K-factor.
- In the inductance pick-up, the permanent magnet is embedded in the rotor. As each blade passes the coil, it generates a voltage pulse. In some designs, only one blade is magnetic and the pulse represents a complete revolution of the rotor.
The outputs of reluctance and inductive pick-up coils are continuous sine waves with the pulse train’s frequency being proportional to the flow rate. At low flow, the output may be on the order of 20 mV peak-to-peak. It is not advisable to transport such a weak signal over long distances and hence, the distance between the pickup and associated display electronics must be short.
- Low maintenance
- Position Insensitive
- Temperature range: -450 to +850 degrees F
- Pressure range: 0 to 20000 psig
- No seals
- Minimal moving parts
- Hydraulic rotor balance
- Ease and cost of installation
- Single flowmeter for wide range
- No seals or expensive bearings to replace
- Ease of installation on new systems or retrofits
- Wide application range from steam to cryogenics
- Wide application range including high-pressure
- No leaks, no replacement or maintenance costs
- Less wear and tear, less expensive
- Enhanced linearity and repeatability
- Ease of sale, increased customer value per unit
Turbine Meter Accuracy
The accuracy of turbine meters is typically given in percentage of actual rate (% AR). This particular meter has a linearity tolerance band of ±0.25% over a 10:1 flow range. The repeatability is from ±0.01% over the linear range. Some minor inconsistencies are introduced during the manufacturing process which requires that all turbine flowmeters be calibrated prior to shipment.
Sizing and Selection
Turbine meters should be sized in a way that the expected average flow is between 60% and 75% of the maximum capacity of the meter. Flow velocities under 1 ft/sec can be insufficient, while velocities in excess of 10 ft/sec can result in excessive wear. Most turbine meters are designed for maximum velocities of 30 ft/sec.
All turbine flowmeters should be sized between 3 and 5 psid pressure drop at maximum flow. As pressure drop increases with the square of flow rate, reducing the meter to the next smaller size will increase the pressure drop considerably.
Viscosity affects the accuracy and linearity of turbine meters. Therefore calibration is important. Repeatability is not greatly affected by changes in viscosity and hence turbine meters are often used to control the flow of viscous fluids.
- Flowmeters should be installed with a minimum of 10 pipe diameters upstream (inlet side) and 5 pipe diameters downstream (outlet side) of straight pipe to prevent errors in measurement caused by swirl, piping alignment or backwash from valves.
- The upstream side should be increased to 20 pipe diameters if the strainer, elbow or tee is upstream of the turbine.
- A partially open gate valve or knife valve also requires a minimum of 20 pipe diameters upstream of the turbine.
- It is suggested that the turbine be installed horizontally. However, the turbine can be installed vertically with no loss of accuracy if these steps are followed:
- a) Flow is upward
- b) Steps 1, 2 and 3 are followed
- c) Flow can be downward as long as pipes are kept full at all times
- If tape or sealant is used on the threaded ends, make sure the last two or three threads are left uncovered so as to not pinch off the tape or sealant and push it into the flowmeter.
- When starting up a line, always have a strainer in place to protect the turbine. Make sure the lines are clean of any foreign debris before start up.
- When starting a liquid line, crack the valves so that entrained air and gas gets dissipated through the flowmeter without excessive rotor speed. This will prevent bearing and rotor damage.
- Should large amounts of air or gas form in liquid lines, a device to eliminate this should be used to prevent measurement error and possible bearing and rotor damage.
- When installing the electronics, keep it away from drips, sprays, splashing fluids and areas that are subject to extremely dirty conditions
The Sponsler Precision Turbine Flowmeters are the most accurate and reliable for both liquids and gases. They exceed the industry standards for high accuracy and reliability over a broad range of products, pressures, flow rates, and operating conditions. They have a long life and can be customized to each customer’s metering needs, including automatic, semi-automatic, and manual applications.
- No Comments
- About IDEX
- Success Stories