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|Troubleshooting the KENT / ABB / AMCO Oil Meter|
The following relates only to oscillating piston flow meters, and specifically
to the Kent Metron or ABB/AMCO series oil meters.
If meter damage occurs, it is almost always when the meter is new, or the piping is being modified and tape, pipe dope, rust, or chunks of product scale wash into the meter.
These meters have four application related failure modes:
1. These meters have very low flow capacity for their line size. They are intended specifically for burner applications where it is common to have a 1/2" or 3/4" line and a flow rate more appropriate for a 1/4" line. If this special function is not recognized, the meter can be easily overrun resulting in premature wearing of the moving parts.
2. The complaint is a stopped meter. This occurs because of poor filtration ahead of the meter. Having a filter ahead of the meter is meaningless unless the strainer is 60 mesh or finer on a 1/2" meter, or 40 mesh on a larger meter.
3. These are oil meters, but because of the low flow characteristic will occasionally be used on other fluids. The meter is copper, bronze and anodized aluminum. As soon as the anodized aluminum piston gets scratched you get a galvanic current flowing between the aluminum and the copper. This results in pitting of the piston which leads to jamming of the piston in the meter.
4. - On the Metron's only ... Meter seems to be working, but the register is not turning. The meter was run backwards, perhaps only briefly, and the driven gear on the underside of the register has unscrewed. This is a left-handed thread gear and if fluid is run in the correct direction, will always tighten, not loosen.
Cleaning up the meter
The working chamber is easy to inspect for damage. Look on the inside walls, top and bottom of the working chamber for scratches or gouges. If you have a deep gouge, you will generally also have a matching gouge in the piston wall.
Scratches on the bottom of the working chamber - if you have light scratching in a oval shaped pattern, this comes from normal wear. In a new meter these scratches come from running a non-lubricating, low viscosity fluid, or by forcing air through the meter to see if it is turning. If the scratches are deep, or not uniformly distributed across the bottom of the chamber, you have had some hard foreign matter in there.
"Nose burn" - this is a deformity in the piston slot where it slides over the diaphragm plate. This is caused by somebody running compressed air through the meter for a prolonged period. The piston wears dramatically and you will see some discoloration due to the heat.
Scratches on the side of the piston and working chamber wall. The gap between the chamber ID and the piston OD is typically .003 to .006 depending on meter size. The two never touch and scratches are always the result of foreign matter.
If the piston does not move easily in the working chamber -
On 1" and smaller oil meters, you can assemble the working chamber with the piston and diaphragm plate and roll it slowly across the table. Gravity should keep the piston at the bottom.
On 1 1/2" and 2" oil meters, you should be able to turn the piston easily with your finger tip.
If it doesn't turn easily, you have either foreign matter or a deformed piston or working chamber.
Broken or bent parts
Every now and then the moment arm (the bar driven by the piston pin) is bent, or the pin on the top of the piston has been snapped off. This occurs when a large piece of matter has jammed the piston and the fluid force has pushed the piston through the jam. The fluid force can be very large, at 100 PSI, a 2" piston will develop about 7500 lbs. of force, which is exerted sideways on the pin and moment arm. When this happens you can generally see a gouge or mark about 1/4 of the way around the chamber from the fluid entrance point.
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