| There are many reasons for selecting helical rotors | | | | the flowmeter. The bent support will also want to |
| over that of flat-bladed rotors. The helical blade | | | | rotate if not properly clamped. |
| transfers energy more efficiently from the flow | | | | Helical rotors do not require bending the supports to |
| stream to the rotor, producing a faster speed of | | | | enhance the linearity. |
| response to flow changes (2-3 mS depending on the | | | | |
| rotor mass and blade area). | | | | Dual-rotor Turbine Concept: |
| Helical rotors also minimize rotor slip in flow startup or | | | | - Unconditioned flow enters flowmeter. |
| stop, representing more accurately the actual flow | | | | - Straightening vanes smooth the flow as it enters |
| rate being measured. This is important if you have a | | | | the first rotor. |
| fluid measurement requirement that is cyclic or | | | | - Flow transfers momentum to the first rotor, making |
| involves short flow bursts, such as in hydraulic | | | | it spin counterclockwise. Flow then exits rotor, with a |
| applications. Helical rotors have less fluid force on the | | | | clockwise spin. |
| bearing, which reduces friction and heat, extending | | | | - Flow enters second rotor with a nearly |
| the life of the bearing. | | | | perpendicular angle of attack, thereby transferring |
| When using flat-bladed rotors, it is often a common | | | | additional momentum to the second rotor. This |
| practice to bend the tip of the support to "trim" the | | | | additional momentum, results in greatly extended |
| flowmeter. Trimming is a term meaning that the flow | | | | turndown. |
| is directed to the rotor blade at an angle to achieve | | | | - Flow exits flowmeter. |
| improved linearity in one direction. In addition, this will | | | | - Dual pickoffs transmit the rotor frequency signal to |
| increase flow resistance and pressure drop across | | | | remote instrumentation. |