Technical Guide
August 2007
TURBINE METER ROTOR AND BEARING DESIGN
The primary differences in turbine meter technology are in the design of the rotor and bearings.
The rotor is an assembly of up to twelve (in some designs this number is greater) blades locked into a hub, which rotates on a bearing or bearings. For light liquid applications that require viscosities of 5 cSt or less, and specific gravities of less than 0.75, the rotor does not normally need a rim (sometimes referred to as a shroud). For measuring the more viscous liquids and in larger size turbine meters (i.e. 8” and above) a rim is fitted to ensure sufficient rigidity in the rotor. A rim also offers the advantage of higher pulse resolution; with a bladed rotor the number of pulses per revolution is limited to the number of blades, and in a rimmed rotor the number of pulses per revolution corresponds to the number of buttons or slots in the rim.
For intermittent duties on light, clean hydrocarbons that may be found at tank truck terminals, ball bearings may be used for a rotor bearing. Proper design of rotors with ball bearings will use two ball races and a short axle upon which the rotor is fitted. Where space is constrained the ball races may be fitted directly into the rotor hub. This design is particularly suited to low and varying flow rate applications, and is utilized on the Daniel Series 1200 Liquid Turbine Flow Meter, designed primarily for distribution applications such as load racks. In these installations, liquids handled are typically light, refined products.
Pipeline applications often require continuous operation at fixed flow rates. Here the design of the turbine meter must offer sufficient longevity to minimize maintenance intervals. In these applications, tungsten carbide journal bearings are used, which offer exceptional longevity. As tungsten carbide is extremely hard wearing, designs utilizing this sort of bearing are often applied to more demanding measurement applications, such as crude oil.
It should be noted here that the limitations on viscosity are related to the rangeability of the turbine flow meter. As the viscosity of the measured liquid increases, the
There may be a single hanger or hangers upstream and downstream of the rotor. In the Daniel Series 1200 Liquid Turbine Flow Meter there is a single upstream support for the rotor, and in the Daniel Series 1500 Liquid Turbine Flow Meter there are both upstream and downstream hangers.
Bearings may be either ball bearings or tungsten carbide journal bearings. Since ball bearings are used to provide improved performance on low flow rates and on clean product, they are a reliable, cost effective solution.
The Daniel Series 1200 Liquid Turbine Flow Meter deploys a cantilevered twin ball bearing design. Utilizing a rotating shaft on two ball bearing units, the Daniel Series 1200 Liquid Turbine Flow Meter is available in 1”, 1.5”, 2”, 3” and 4” line sizes. For more demanding applications, a tungsten carbide journal bearing assembly is available as an option.
Lightweight bladed rotors of this type mounted on ball bearings are particularly suited to the intermittent duty cycles typical in loading rack applications. The design application is limited to clean refined products. In the event that the turbine is used on slightly dirty products, the use of tungsten carbide journal bearings is recommended. Tungsten carbide bearings are extremely hard wearing and used in turbine meters on a range of applications from LPGs to crude oils.
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