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Draft Transmitter Enclosure

VIPAK Draft Range Transmitter Enclosures
  • Overview +


    A Complete System
    Low pressure draft range DP transmitters for furnace, heater and boiler control are problematic.  They are affected by wind and weather changes. Many solutions have been attempted to ‘solve’ the problem but none have been universally successful until now. 

    Proven Solution
    The O'Brien VIPAK Draft Transmitter enclosure, is a field tested and proven solution addressing the common sources of draft transmitter installation error with:

    • Still Air Chamber
    • Atmospheric Equalization
    • Uniform Capsule Temperature

    Pressure measurement in furnace and boiler combustion is critical for safety, efficiency and environmental control. The pressure is extremely low, often in the range of -1.0 to +2.0” H2O and installation problems that would normally be inconsequential can wreak havoc with draft range systems. Using a differential pressure transmitter the reference measurement is vented to atmosphere where air flowing past the open port creates pressure changes and errors in furnace, heater and boiler combustion box pressure. As part of the Safety Instrumented System these measurement errors can create nuisance maintenance and shutdowns affecting the entire unit.

    C31 Draft Range Transmitter Enclosure 

    The O'Brien STILL AIR PORT is an integral part of the draft range transmitter solution.

    O'Brien Still Air Port 

    The O'Brien VIPAK draft range transmitter enclosure atmospherically equalizes the still air chamber for the transmitter and manifold. The pressure inside the enclosure changes at the same rate as the barometric pressure but is unaffected by wind or wind gusts. The enclosure system also ensures that both sides of the instrument measurement capsule are at the same temperature. Since these instruments are often placed near the furnace, heater or boiler one side can be hotter than the other creating an error in measurement.

    Current installation configurations fail to protect atmospheric port from the effect of wind and weather.

    Current state for draft transmitters 

    Customer Experience
    A large gulf coast refinery was experiencing furnace upsets and shutdowns caused by storms and wind in the unit. They installed two O'Brien Draft Transmitter Enclosures on their most trouble prone units as a trial.

    After a severe storm hit and the units with the O'Brien Draft Transmitter enclosures ran with no problems they installed another 128 protection enclosures.
    To date there have been no more upsets or shutdowns caused by wind induced measurement errors.

  • Solutions for Single Draft Range Transmitters +


    C31-19137 draft range transmitter enclosure 


    A1T-19138 draft range transmitter enclosure
  • Solutions for Draft Transmitter Poling +


    A3T3-19139 draft range transmitter enclosure for poling
  • Additional Accessories +

    Accessories are ordered separately and easily fitted to the enclosure package.

    Electric Heaters
    For cold temperature installations or wet sample applications enclosure heaters may be added as well as heat traced or insulated impulse tubing.

    For Single Enclosures
    Order: TS3115D2CJS1H
    120V 150W CL I, Div 2 Gp ABCD FM/CSA heater protects down to -40°F/°C

    For PolingEnclosures
    Order: TE3130D2CJS1H
    120V 300W CL I, Div 2 Gp ABCD FM/CSA heater protects down to -40°F/°C


    Instrument Connection Kit
    Order: IPK1
    Instrument power/signal connection kit. Suitable for use in CL I, Div 2 areas.


    Heat traced and Insulated Impulse Lines
    For electric traced or pre-insulated impulse lines consult local representative or factory and order S-Line tubing or TRACEPAK bundle with TPKES-4S heat shrink entry seal.


    Internal Static Air Baffle
    Some specifications require a static air baffle mounted directly to the ambient sensing port of the transmitter. O'Brien offers two standard units:

    Order: BDT6
    Internal manifold mounted static filter, replaces the compression nut and ferrules of a customer supplied 3/8" tube fitting. Equalization 0.07 ft3/hr Rated for 11.4 mph wind speed.
    Order: AMCSAPPSS
    Internal manifold mounted static filter. Attaches to customer supplied 1/2" NPT threaded connection. Rated for 11.4 mph wind speed.
  • Literature +