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Model 271 Non-Heated Sample Probe

Model 271 Non-Heated Sample Probe
A complete 271 assembly is comprised of a Probe Tip Filter, a probe tube with both ends threaded and the isolation /blowback assembly mounted in a NEMA 4X Fiberglass Enclosure. The probe tip filter varies in size, material of construction and function depending on the application. Each application will determine the appropriate probe tip filter. The diameter of the stack will determine the length of the probe tube. The probe tube length should be such as to place the probe tip filter in the middle third of the stack.

The NEMA 4X enclosure is fastened directly to the mounting flange, which is sized to match the mating nozzle flange on the stack. There is a heat shrink boot on the bottom of the enclosure to accept a Heated Sample Line (HSL). When the HSL is properly supported, the flange mounting of the 271 is sufficient to support the entire assembly.

Two blowback accumulators (each consisting of a 7” dia. stainless steel sphere) are designed to be pressurized to a maximum pressure of 125 psig compressed air. At that pressure there is 1.4 cubic feet of air stored to flush the particulate matter out of the filter and into the stack. This air supplied to the blowback assembly needs to be clean and dry. Instrument quality air is preferred. The pressure should be as high as possible, up to 125 psig. High pressure air fills the accumulator and provides a substantial blast when the solenoid valve opens. This loosens the particles on the filter surface and forces them back into the stack. The period of time between blowback cycles should occur before the pressure drop across the filter begins to increase. This should be selected to 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.

A sample isolation cap is provided for when the probe tube and probe tip filter are changed. Please see the “Changing the Sample Filter” section of the product manual for instructions regarding filter replacement.


  • Dual Accumulators
  • High flow explosion proof 3 way blowback/sample valve
  • Large filtered surface area
  • Optional enclosure heater


  • High Dust
  • Low Moisture
  • Non-Heated
  • Coal-BMS

Technical Specifications

  • Sample Flow Rate: 0 TO 20 LPM
  • Calibration Gas Requirement: Sample Flow Rate Plus 10%
  • Operating Pressure Drop at 10 LPM: 12" Water Column
  • Maximum Gas Temperature at Inlet: 750°F (316SS) - 1475°F (Hastelloy C276)
  • Dimensions (H x W x D): 18" x 16" x 10" (Fiberglass) - 19" x 17" x 14.5" (304SS)
  • Weight: 25 LB (9 KG) (Minus Probe and Filter)
  • Input Power Requirement: 24 Watts*
  • Input Voltage Requirement: 24VDC or 115VAC or 230VAC (@ 50/60 HZ)
  • Blowback Tank Volume: 1.4 SCF @ 100 PSIG
  • Blowback Duration: Two Seconds (Recommend)
  • Blowback Frequency: W/O Timer Card - External Control W/ Timer Card - 15 Min. to 24 Hr.
  • Blowback Solenoid Valve Voltage: W/O Timer Card - 24VDC or 115VAC or 230VAC W/ Timer Card – 115VAC or 230VAC

* See Manual for Wattage w/Heated Enclosure