Description And Principle Of Operation - Ametek 270SF Instruction Manual

Description and Principle of Operation

APPLICATION
The Universal Analyzers Model 270SF Extractive Gas Sample Probe Assembly is designed to be installed on sample
stacks containing non hazardous gases. The 270 may be installed in an unclassified location. Filter changes can be made
in less than one minute.
The 270SF filter will mount by means of a pipe flange to a mating flange on the stack. The size of the flange can be
specified by the user and can include 2", 3", 4", 6" or DIN type. A 1/2" NPT female threaded connection is provided for the
sample probe to mount inside the mounting flange. Stack temperatures and corrosive gases will determine the material
and design of the probe to be used.
Sample flow rates of up to 20 liters per minute can be extracted and filtered through the Model 270 with a minimal amount
of pressure drop.
GENERAL DESCRIPTION, HEATED FILTER SECTION
The Model 270SF is a Extractive Gas Sample Probe Assembly consisting of the filter body mounted in a NEMA 4X
Fiberglass Enclosure or Stainless Steel Enclosure. An optional blowback system is provided to allow the blowback to
occur on command from a computer, data logger, PLC, UAI timer card or external switch mounted in a safe area.
Two 63 watt heaters are mounted in an aluminum sleeve around the filter cavity. The heater holds the temperature of the
filter at 340°F (171°C). A hermetically sealed bi-metallic thermal switch mounted to the filter body keeps the temperature
from exceeding 350°F (177°C) by opening the circuit at that temperature. An optional independent temperature sensor
can be provided as a means to measure and transmit or record the temperature of the filter. A second thermal switch, set
at 225°F (107°C) is provided to be used as an alarm contact, if the temperature drops below the switch temperature. In
colder climates, an additional heater can be supplied for the enclosure. This heater will maintain 150°F (65°C) inside the
enclosure.
Several types of filter elements can be supplied with the Model 270. The 2 µm ceramic filter is supplied as an economical
general purpose filter. A similar ceramic filter with an internal 0.1 µm coating is available for finer filtration or to provide a
surface to enhance the blowback capability where the particulates have a tendency to fill the pores of the 2 µm element.
A 2 µm, 316SS Filter can be inserted for those applications where the ceramic filter is determined to be unsuitable.
Additional filtration materials and pore sizes are available on request.
Blowback air is used to clean the filter element. Compressed air supplied to the blowback assembly needs to be clean
and dry (-40°F/°C recommended). Instrument quality air is preferred. The pressure should be as high as possible, up to
125 psig (8.8 barg). High pressure air fills the accumulator (a 7" (178mm) diameter SS sphere) and provides a substantial
blast when the high flow solenoid valve opens. This loosens the particles on the filter surface and forces them back
through the sample probe into the sample point. The period of time between blowback cycles should be set to occur
before the pressure drop across the filter begins to increase beyond acceptable limits. By installing and monitoring a
vacuum gauge ahead of the sample pump, a maintenance interval can be established. This can be as often as every
fifteen minutes but no less frequently than once per day. The time period between blowback cycles can be based on a
calculation to estimate the amount of sample required to deposit from three to five grams of solids in the filter element.
Instrument air usage is minimal and smoothed by the fact that the air accumulator is charged over a period of time through
a 1/4" instrument air line. The recharge time could be extended with a restriction in the air line if it were desired to reduce
the pressure pulses on the instrument air supply and to consume instrument air more slowly.
The calibration gas is injected into the chamber ahead of the filter. This is close to the sample source, as is required by
many EPA officers. A back pressure check valve (set at 3 psig (0.2 barg) is provided in the cal gas injection path to insure
that calibration gas does not leak into the sample while the sample is being drawn through the filter.
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MAN.270SF.REVA.12222014