Results 1 to 2 of 2
  1. #1
    Join Date
    Sep 2007
    Location
    Somerset
    Age
    63
    Posts
    4,502
    Rep Power
    38

    Acceptable Differential between a H.P. Cut-Out and PRV>



    Hands up!
    How many Techs out there would assume 4 bar (approx 60psi).
    Was a satisfactory differential between a systems H.P Cut-out setting and The HP PRV setting?

    Basically we had a situation recently where a system condenser fan speed inverter received a electrical spike.
    Causing the fans to stop and the H.P pressure to rise to-wards it's H.P. cut-out setting of 20.0 bar.
    (H.P. PRV set at 24.0 bar)
    3 comps on a common circuit with individual mechanical HP cut-outs.
    Comp 1 trips on H.P. comps 2 and 3 do not.
    The PRV lifts and then resets!
    When the above was re-simulated.
    Comp 1 H.P. cut-out at approx 20 bar whereas the other 2 stayed shut until the Technician shut the system down at 21/21.5 bar for fear of lifting the PRV again.

    This system is periodically tested for H.P. cut-out operation.
    Yet because of the inaccuracy of Mechanical HP switches and a possibly slightly low 24bar set PRV.
    A reasonable 4bar diff was proved to be un-suffice!

    Obviously we have recommended their replacement.
    And I suspect these will be wired in series not parallel as before.
    Can anyone think of a reason why they are individually wired?
    A long story I know but maybe someone will benefit
    Moral.... Periodic reset using nitrogen of the pressure switches is recommended!
    Cheers Grizzly



  2. #2
    Join Date
    Jun 2001
    Location
    N.Ireland
    Age
    44
    Posts
    1,632
    Rep Power
    18

    Re: Acceptable Differential between a H.P. Cut-Out and PRV>

    Quote Originally Posted by Grizzly View Post
    Hands up!
    How many Techs out there would assume 4 bar (approx 60psi).
    Was a satisfactory differential between a systems H.P Cut-out setting and The HP PRV setting?

    Basically we had a situation recently where a system condenser fan speed inverter received a electrical spike.
    Causing the fans to stop and the H.P pressure to rise to-wards it's H.P. cut-out setting of 20.0 bar.
    (H.P. PRV set at 24.0 bar)
    3 comps on a common circuit with individual mechanical HP cut-outs.
    Comp 1 trips on H.P. comps 2 and 3 do not.
    The PRV lifts and then resets!
    When the above was re-simulated.
    Comp 1 H.P. cut-out at approx 20 bar whereas the other 2 stayed shut until the Technician shut the system down at 21/21.5 bar for fear of lifting the PRV again.

    This system is periodically tested for H.P. cut-out operation.
    Yet because of the inaccuracy of Mechanical HP switches and a possibly slightly low 24bar set PRV.
    A reasonable 4bar diff was proved to be un-suffice!

    Obviously we have recommended their replacement.
    And I suspect these will be wired in series not parallel as before.
    Can anyone think of a reason why they are individually wired?
    A long story I know but maybe someone will benefit
    Moral.... Periodic reset using nitrogen of the pressure switches is recommended!
    Cheers Grizzly
    Hello Grizzly

    my reading on it is H.P. cutout staggered up to 0.9 of PRV value. I would tend to use a manual reset HP but keep a good range between each compressor cutout. HP should be wired directly on the safety chain to the compressor starter.
    All safety settings should be checked each year as part of the maintenance.

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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •