micro-trak MT-3405F II, Справочное руководство

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49
Appendix E
(cont)
Field Operation - Troubleshooting for NH3
Always follow accepted safety precautions. Make sure that
equipment is in good operating order. Before connecting
the nurse tank to the applicator, check the electric shut-off
valve of the MT-3405F™ II system for proper operation.
After changing nurse tanks or after other periods of long
shut-down, operate the system in MAN until the application
rate stabilizes. This allows the heat exchanger to reach
operating temperature before selecting AUTO. Erratic
operation may be experienced if AUTO is selected before
operating temperature is reached.
Manifold pressure is very important for good distribution
of NH3. Use barbed fittings with properly sized orifices or
an adjustable manifold to maintain adequate pressure. If
manifold back pressure is too low, proper cooling will not
be achieved, vapor bubbles will be allowed to enter the
flowmeter, and readings will be inaccurate. Typical manifold
pressure ranges from 15 to 60 PSI (1 to 4 bar) depending
on application rates and ambient temperature. If manifold
pressure stops climbing but FLOW RATE continues to climb,
vapor bubbles are present.
In hilly or rough conditions the nurse tank dip tube will not
remain submerged, allowing extra vapor in the system. This
vapor is to too much for the heat exchanger to condense
and the system will exhibit erratic operation. If the dip tube
remains out of liquid, operation may appear to be normal,
but the system is simply metering vapor. If this occurs,
you will notice extremely low manifold pressure. Change
tanks before the NH3 level is low enough to cause these
problems.
In NH3 control systems, location of the frost build-up is an
indication of system performance. The NH3 kit will normally
have frost on the output side of the servo valve and in some
cases, a small amount on the bottom portion of the heat
exchanger. Frost before the servo valve indicates excessive
pressure drop in the delivery system or restricted vapor
lines.
The strainer is a common source of excessive pressure drop
and should be cleaned regularly. AFTER COMPLETELY
DRAINING THE SYSTEM, remove the large plug and
carefully clean the strainer’s screen. Also, periodically check
the vapor tubes for obstructions.
Additional Troubleshooting Tips for NH3
See Troubleshooting section, starting on page 33.