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  1. #1
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    TXV Bulb placement



    I've run across a good size (450k BTU/h) chiller and am puzzled by the placement of the bulbs for the expansion valves (Alco THR).

    On a similar chiller, the TXV bulbs were located at the lower quadrants of the suction line leaving the evaporator.

    On this unit, the bulbs are located at the very top of the suction lines. A location I've only used ir seen on quite small systems.

    The rule of thumb I've followed in the past (if no data sheets with placement info) is that on small scale systems, with 3/4 or smaller suction lines, the bulb goes at the top and on larger suction lines, the bulb goes at the 4 or 8 o'clock position.

    Alco's own data sheet suggests the 4 or 8 o'clock position so I'm curious to the original manufacturer's decision to place the bulbs at the very top of the line.

    What changes to the behavior of the TXV will occur with changes to the bulb location?

    While I'm curious, I'm a bit hesitant to start moving the bulbs around just to see what happens!



  2. #2
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    Re: TXV Bulb placement

    Quote Originally Posted by dkemper View Post
    I've run across a good size (450k BTU/h) chiller and am puzzled by the placement of the bulbs for the expansion valves (Alco THR).

    On a similar chiller, the TXV bulbs were located at the lower quadrants of the suction line leaving the evaporator.

    On this unit, the bulbs are located at the very top of the suction lines. A location I've only used ir seen on quite small systems.

    The rule of thumb I've followed in the past (if no data sheets with placement info) is that on small scale systems, with 3/4 or smaller suction lines, the bulb goes at the top and on larger suction lines, the bulb goes at the 4 or 8 o'clock position.

    Alco's own data sheet suggests the 4 or 8 o'clock position so I'm curious to the original manufacturer's decision to place the bulbs at the very top of the line.

    What changes to the behavior of the TXV will occur with changes to the bulb location?



    While I'm curious, I'm a bit hesitant to start moving the bulbs around just to see what happens!
    Hi Kemper

    I would say the manufacturer of the valve is probably right and the chiller manufacturer has either got it wrong or they have a hunting problem that is not fully resolved.

    Kind Regards Andy
    If you can't fix it leave it that no one else will:rolleyes:

  3. #3
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    Re: TXV Bulb placement

    The placement at the very top may be aimed at preventing the isolating action of oil inside the pipes.
    Oil prevents a fast energy transfer .

  4. #4
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    Re: TXV Bulb placement

    yes, in most cases, i follow that of the TXV supplier/manufacturer's details.

    but, there is so abnormal event where i do deviate its installation location.

    yeah .. oil may be any issue or cause of such deviation.

    system design esp. piping size, flow velocity, bulb location & its ambient etc & etc....

    it is still worth being adventurous ...

  5. #5
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    Re: TXV Bulb placement

    I am used to seeing the bulbs location at 4 or 8 0clock position, as it needs to sense the liquid and vapor phase temps.

    I am going to make a guess here that maybe the evap or air flow of this system may be undersized causing the super heat to be more of a flooded condition. If this is the case then the higher the bulb the better.

    I may also prosume that maybe a tech that assembled this unit was not paying attention of where the bulb mounts location, or even maybe a newbie tech was dispatched to this unit prior to you and had serviced or replaced the TXV valve, and just mounted it and called it good. or maybe the unit was not superheating correctly and this was how it was temporarly repaired.

    Who Knows? I try never to take for granted the guy before me did it right.....

    Have you tried locating the sense bulb and checked the super heat?

    A-Z

  6. #6
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    Re: TXV Bulb placement

    yes, esp. when your predecessor has undersized the suction line ... you just can't get the right superheat.

    hope that's not your case/s.

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