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|Troubleshooting the Sponsler Turbine|
Problem - your customer is reporting incorrect readings from a Sponsler
Specific problem - the display reading is always off by the same amount.
This is a K-Factor problem in the receiving device. The flow meter comes with calibration data based on it's performance in their test stand. The actual installation is seldom the same and the difference results in a constant error in the readout. The fix - set the K-factor to zero and run a known volume of fluid. Divide the # of counts in the display by the volume and this is the correct # of pulses/unit volume, i.e. the correct K-Factor.
Specific problem - the display reads correctly at low flows, but goes off at higher flow rates.
This is a piping problem. The meter is installed to close to a elbow, or similar. At low flows the fluid coming into the meter is relatively laminar, at higher flow rates it becomes non laminar and the rotor sees a force imbalance due to different impact velocities. The rule of thumb is to have 10 pipe diameters upstream and 5 downstream. A better approach, which covers all piping conditions, is to use the ASME tables for installation of orifice plates and treat the turbine meter as a plate with a Beta = 0.8.
Specific problem - the meter display runs fast then slow, or exhibits jitters.
This is normally air in the lines, or electrical noise pickup in the wiring to the display device. If the turbine does not have a transmitter, then the receiving device has a front end amplifier capable of handling millivolt signals, which makes it a good receiver for electrical noise.
To check for electrical noise - ensure that the cable to the pickup is not grounded at the pickup, only at the receiver. Disconnect the pickup connector and see if the noise stops.
To check for air - take a long shafted screwdriver and hold it against the body with the other end in your ear. You should hear a faint whirling noise as the rotor spins. If you hear pops or low grinding noise you have air or some foreign matter.
Specific problem - the meter does not run at low flow rates.
The meter is oversized.
Failure modes for turbines - The most common problem is material getting washed into the meter internals. We are forever getting meters in with teflon tape wrapped around the rotor shaft, or gunked up with pipe dope.
To check a turbine ...
Question - Is the rotor turning?
With flow going through the meter, place a long stemmed screwdriver tightly against the meter body and the other end in your ear. You can hear the turbine turning.
a. Take it out of the line and examine the blades for damage, the blades don't bend easily. You will seldom see a bent blade, but if it was impacted with a rock it may be missing a blade.
b. Spin the rotor by blowing through it with your breath. It should spin very easily and then as it comes to a stop will line up with a blade opposite the magnetic pickup. The rotor may overshoot and return back to a position lining up the rotor blade.
c. Meters that have had fluids dry in the meter can develop a coating on the sleeve bearing which does not clean out easily. The meter runs, but very poorly at the low end and better at high velocities. Eventually, the coating normally goes back into solution and the meter runs properly. Surprisingly, this even happens with acids, nitric comes to mind.
d. Don't overlook the electronics on the meter. If it has a transmitter, somebody could have turned down the sensitivity, killing the low flow response or totally eliminating any output.
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