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  1. b7031719

    Choked Flow in Backpressure Valves

    Hi LittleInch thanks for the reply. I take your point I guess back pressure regulator is not the correct terminology at all and thanks for pointing this out. I suppose really the question is why does the IEC standard require the choked flow pressure drop to be used for the sizing pressure drop...
  2. b7031719

    Choked Flow in Backpressure Valves

    OK thank you for the reply. If the downstream pressure is constant, let's say atmospheric pressure, which is the case for my application. As the upstream pressure increases as will flow, until choked flow occurs then what? What if the upstream pressure then increases further?
  3. b7031719

    Choked Flow in Backpressure Valves

    Well there can only be one correct answer. Either IEC is correct for pressure reducing and backpressure service, that only upstream pressure changes can increase the flow beyond choked pressure drop, which implies there is no choked flow for backpressure service. Or the statement only applies...
  4. b7031719

    Choked Flow in Backpressure Valves

    I think the statement in IEC 60534-2-1 is misleading then, based on what you are saying. For backpressure valves the statement should read:
  5. b7031719

    Choked Flow in Backpressure Valves

    Hi thanks for the reply. In this particular case I am interested in, the dP does result in choked flow.
  6. b7031719

    Choked Flow in Backpressure Valves

    The definition of choked flow in IEC 60534-2-1 is: My question is, does this apply for backpressure valves where the upstream pressure varies at constant downstream pressure? My sizing calculation for a backpressure application has used the choked flow pressure drop for the sizing pressure drop...
  7. b7031719

    Allen Bradley Logix5555 Memory

    Hi thanks for the reply. That is interesting because I have seen some YouTube videos demonstrating the complete loss of application program when the battery is removed and main power is off. In my case I have a 1756-L55 processor, FW version 8.21 that has been without power for a few years now...
  8. b7031719

    Pump Relief PCV Sizing

    Yes actually it is a modification that I would like the pump manufacturer to supply I am just interested in the process. There is a closed-loop pressure control system doing this job currently but fitted back in the early 80s and is in need of replacement. I was thinking a regulator would be...
  9. b7031719

    Flow Meter Gauge Scale Factor

    I have seen a few differential pressure gauges now with a logarithmic scale in flow units and a scale factor written on the dial e.g. x600 IGPM etc. What is the reason for the x600 scale?
  10. b7031719

    Allen Bradley Logix5555 Memory

    What purpose is the battery on the Logix5555 processors? Is the application program stored on some sort of internal SRAM that requires battery backup in case of main power failure? I have also read that some of the processors can come with or be retrofitted with a flash memory module or compact...
  11. b7031719

    Pump Relief PCV Sizing

    Thanks for your help this is interesting. I will contact the original pump manufacturer to get some more advice.
  12. b7031719

    Pump Relief PCV Sizing

    OK so the weekly test is supposed to be done using some manual dump then opened for testing purposes only?
  13. b7031719

    Pump Relief PCV Sizing

    Hi thanks again for the reply. I got this wrong actually it is a centrifugal pump although I doubt this changes things much? I do have a copy of NFPA 20 and will take a look at the requirements in there thanks for the reminder.
  14. b7031719

    Pump Relief PCV Sizing

    Hi thanks for the reply. This is a pump governor regulator e.g. Fisher 1B-R for regulating system pressure downstream of the pump (positive displacement). The system demand varies quite a bit (fire water system supplying deluge in various zones).
  15. b7031719

    Pump Relief PCV Sizing

    If I wanted to size a regulator that is to be installed in bypass around a pump i.e. back-pressure regulator and I know the desired back-pressure how do I determine the size of the valve based on the pump curve?
  16. b7031719

    Limiting PID Output

    I am asked if it is possible to limit the output of a PID controller by putting a software restriction on the output signal to the actuator. In this case it is a temperature controller on a fired heater and is regulating heat input into the system and controlling output temperature. The...
  17. b7031719

    Centre Tapped Input to Power Supply

    Thanks for the comments. I have been in contact with the manufacturer of the power supply (Relec W Series). It has been confirmed that it is suitable to be operated with this kind of supply however they do offer an optional built-in secondary fuse in the neutral, presumably for this kind of...
  18. b7031719

    Centre Tapped Input to Power Supply

    Thanks for the reply. This is an industrial installation, the supply is coming from a UPS not an isolation transformer. The UPS was specified to be 55-0-55V a.c. and supplies many other loads. Unfortunately there isn't an opportunity to modify for this particular case so I am trying to...
  19. b7031719

    Centre Tapped Input to Power Supply

    I have come across a 110V a.c. switched mode power supply that shows Live, Neutral and Earth input terminals and includes fuse and VDR input protection but does not state whether a 55-0-55V a.c. input is acceptable. In general are centre-tapped supplies a problem for power supply inputs?

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