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Installing Low-Flow Fuel Transducers
Low-flow fuel transducers are precision devices. These turbine flow meters incorporate ultra-low friction (jeweled) bearings with lightweight paddle-wheel rotors ruining super-tight clearances. They must be treated with the care that such laboratory-grade instrumentation deserves.
a) The low-flow fuel transducer, due to its sensitivity, must be unpacked and handled carefully. Make certain that the transducer is clean and free from packing materials or debris.
CAUTION: DYNOmite low-flow fuel transducers are precision instruments and will be damaged if a shop-air hose is used for cleaning or checking the rotation of the transducer’s rotor.
b) The transducer must be spliced into the engine’s fuel inlet line. The arrow on the transducer body indicate the direction of fuel flow.
Tip: Most fuel pumps tolerate the added flow restriction of the transducer better if the transducer is installed after the fuel pump rather than on its suction side. If your engine has multiple fuel pumps and/or carburetors, you should “T” the lines together where they exit at the outlet of the fuel pumps and then split them again after the transducer with another “T” to go to the carburetors.
c) Inlet and outlet ports are indicated on the housing by observing the flow direction arrow. The transducer’s design makes it quite insensitive to upstream or downstream fluid flow disturbances, therefore, it is not necessary to be concerned about the length of the straight-line run either upstream or downstream of the transducer. However, the inside diameter of all connecting plumbing must be larger than the transducer’s orifice.
Tip: Filtering is recommended, both upstream (to 100 microns) to protect the transducer from debris, and downstream, to protect your equipment – from dislodged parts, in the event of a turbine-wheel failure.
d) The connecting plumbing must not impose any bending stresses on the transducer housing or end connections.
e) The transducer should be located upstream of all final control elements, bypass throttling, or on-off valves. It should never be installed so the transducer drains completely when flow ceases.
CAUTION: Hydraulic hammering is a term used during start-up (initial introduction of fuel into the lines) to describe a high velocity flow impacting on the transducer’s rotor. This must be avoided to prevent damage to the mechanical parts. Pressure should be built up gradually, at initial start-up, to avoid damage from over-speeding the rotor. Severe hydraulic hammering, from improper start-up or flow surges during operation, must be avoided to prevent shaft or rotor-blade breakage.
Tip: Care should be taken not to locate the transducer or connector cable in close proximity to strong electro-magnetic fields such as electric motors, transformers, spark-ignition components, or other high-voltage lines. These may induce spurious signals in the pickup coil or cable.
f) Pickups should bottom out in the well of the transducer housing but should only be finger tightened, to approximately 4 in-lb, to prevent distortion of the coil housing. The pickup is secured in position by tightening the lock nut to approximately 25 in-lb. The pickup is removed by loosening the hex lock nut and unscrewing the pickup from the housing.
1) Select a convenient location in the test cell where you can mount the transducer that will be free from vibration.
Tip: For improved fuel flow on marginal fuel delivery installations, avoid mounting the transducer or hoses higher than the fuel pump(s).
2) Mount the transducer with the rotor shaft horizontal and the pickup vertical (wires exit up). A vapor separator ahead of the transducer will prevent misreading of air bubbles as fuel.
Tip: For engines equipped with a fuel bypass return line (i.e. most fuel injected engines) the transducer needs to be installed on the engine side of the return branch. Otherwise it will inappropriately record flow bypassed to the tank! Alternatively, a second transducer may be inserted into the return line with DYNO-MAX used to mathematically subtract the bypassed flow from the indicated fuel consumption.
3) The connecting plumbing must not impose any bending stresses on the transducer housing or end connections.
4) Plug the transducer’s 3-pin male connector into the DYNOmite’s (Frequency 3) “Fuel Flow (in)” lead (found on the optional “Full-Function” harness).
CAUTION: Once a low-flow fuel transducer has been installed, the greatest hazard is over ranging the device (e.g. running more than 10% over range). These transducers remain quite linear when they are over ranged, and it may not be immediately apparent that the device is being misused. However, the pressure drop will become excessive, and over-speeding of its jewel bearings and rotor will cause permanent damage.
Besides damage from improper checking of the transducer with a shop-air line, the next two most common reasons for over-speeding are:
a) Miss sizing the flow transducer for the application. If the system will ever flow more fuel than the transducer’s maximum range – do not install it.
b) Failure to bleed the system before allowing full fuel flow (e.g. starting when there is still air in the lines). Air must be bled carefully from lines before high flow range is established – or the upstream flow restricted so that it can never exceed the transducer’s maximum flow range.
Tip: When used below the minimum specified range, turbine-type fuel transducers may become very non-linear due to clearance leakage and bearing drag.
Maintenance of the low-flow fuel transducer consists of periodic inspection to insure that the internal parts have not been fouled or suffered any corrosion. Should the assembly be damaged in any fashion, it should be returned to the factory for repair.
Turbine-type transducers are precision devices and must be treated as such. The freedom with which the rotor is allowed to rotate is the major contributor to this precision. The majority of fuels measured by turbine meters contain impurities, which if allowed to remain within the transducer after use, would form hard or gummy residues. When these residues are deposited within the transducer, the unit’s freedom of rotation will be severely degraded. Therefore, it is highly recommended that whenever possible the turbine meter should be THOROUGHLY FLUSHED with an appropriate solvent immediately after use. The solvent should be chemically neutral, and HIGHLY VOLATILE so that COMPLETE DRYING can take place soon after the flushing operation. Some appropriate solvents would be ethyl alcohol, stoddard solvent, or trichloroethane.
CAUTION: DO NOT OVER SPEED BEARINGS. Care must be taken when flushing the transducer, not to over-speed or otherwise damage the bearings and rotor assembly.