Loss of Pressure - QMDI Classic

Discussion in 'DI Presses' started by maverick1971, Jul 15, 2017.

  1. maverick1971

    maverick1971 Senior Member

    Joined:
    Jul 2011
    Messages:
    126
    Location:
    South Africa
    Hi everyone!
    I am having a problem on my QMDI CLASSIC.
    The press is sometimes losing pressure on start up. Pressure starts dropping as soon as we go onto impression. Drops suddenly from 9.5 bar to below 6 bar quite quickly. This however does not happen on every start up which is confusing. We have checked all the short stroke cylinders and have replaced one which had a slow leak around the shaft. The others all seem fine. All the air lines have been checked several times also - no leaks.
    Some of the long stroke cylinders did have minor leaks and all of these have been replaced. So we no longer have any obvious leaks on the press but we are still experiencing a sudden loss of pressure on start up (randomly).
    Can anyone please advise on what else we could check? The compressor is running fine - cuts off and starts up properly. I am at a loss at this point. Any help would be appreciated.
    A point to note though - if we start running and we notice the pressure dropping - we stop impression, leave the press running and the pressure builds up again. We then go to impression again and the press runs fine. Really confusing!!!
    Please let me know if anyone out there has any suggestions.........
    Thank you
     
  2. CHOCK

    CHOCK Senior Member

    Joined:
    Dec 2016
    Messages:
    443
    Location:
    Managua
    Dear Sir:
    Hi hope you are well.
    The tank is equipped with presurre switches S26 +F45+Drain Valve Y30,see the schematic d.
    Test:1) Pressure switch S26 this control automatically the ON and OFF of the compressor.
    When the pressure reach 8.5bars, IT switches the compressor OFF. If the pressure in the pressure
    tank fall below 6.5bars, it switches the compressor ON again.
    Test :2 Pressure switch F 45, this responde with a pressure 7.5 bars is reached.If the pressure Drop
    to 6.5bars signal is send to electronic system( to due insufficiente air system). This switch is Set in the
    factory.The fault can be cancelled when the pressures reach 7.5 bars Again.
    3) Drain Valve Y30: The electronic system of the machine open the Valve by 2 seconds each 20 minutes.
    If the valve can be defective, can be do it manually.Repair or replace.
    Of course ANY LEAKING is will be a PROBLEM, that will be eliminated Inmediately, otherwise, you will
    have Erratic Problem, confusing the electronic system of the machine.
    Let me know any question or doubt
    Blessing
    superchock@yandex.com
     
  3. maverick1971

    maverick1971 Senior Member

    Joined:
    Jul 2011
    Messages:
    126
    Location:
    South Africa
    Hi CHOCK,

    Thank you for your reply to my thread. The compressor and the switches you mentioned seem to be fine. When we switch the machine on the compressor comes on as usual and builds up pressure to around 8 car which then sigmals the machine is ready. When the pressure drops to around 7,5 bar the compressor starts up again. The drain valve seems to be working fine also - I actually replaced it thinking this was the problem. So we have the 2 switches working as designed, the drain valve functioning as it should and no leaks on the compressor.

    The problem of losing pressure only occurs "sometimes" when we go onto impression mode. The machines starts to print on all 4 units but the pressure starts to drop quickly - indicating a leak somewhere. However - if we stop, wait about 10 seconds and start up again, the machine runs as normal. This is strange because we cannot seem to find any leaks on the short stroke cylinders/pistons and we have replaced all of the faulty long stroke cylinders/pistons. All pipes have been checked and there is no visible/audible leak anywher on the press.

    One question please - Does the 3/2 Valve on the machine have anything to do with a loss of pressure? Can this cause the problem erratically?

    Your feedback would be most welcomed.

    Thank you again!

    Regards - Shawn
     
  4. CHOCK

    CHOCK Senior Member

    Joined:
    Dec 2016
    Messages:
    443
    Location:
    Managua
    Hi sir
    As i did indicate, any Devices has many anything to do with a loos of pressure/
    Remember this system had been designed with Software in electronic system (CPU)or microprocessor, they communicate
    in intelligent way to the machine, in that way they give the ok or bad signal to the machine. and inmediately ocurr the
    Failure.
    Remember as a software eng, ANY machine that had been Programmed, ObEY ASAP, when some parameter occur , to designer of the Developer Software Machine.
    Regards
    superchock@yandex.com
     
  5. maverick1971

    maverick1971 Senior Member

    Joined:
    Jul 2011
    Messages:
    126
    Location:
    South Africa
    Hi CHOCK,

    Thank you again for your reply. We eventually found the problem / leak!!

    The long stroke piston/cylinder Y2 on the DS was leaking on start up (intermittently)
    We ran the press with the doors open and noticed the leak when the pressure dropped.

    It was actually a faulty VALVE and not the actual cylinder/piston. I replaced the valve and that has solved the problem.
    Can you please tell me - Is it possible to service/repair these valves? We have had quite a few that have failed in the past few weeks and it is proving to be rather costly to constatly replacethese valves.
    Do you know if we can refurbish them or what is the cause of the valve failure? Your advice would be welcomed.

    Kind Regards

    Shawn
     

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  6. CHOCK

    CHOCK Senior Member

    Joined:
    Dec 2016
    Messages:
    443
    Location:
    Managua
    Hi sir
    Great that you fix it. as did suggest
    ¨Of course ANY LEAKING is will be a PROBLEM, that will be eliminated Inmediately, otherwise, you will
    have Erratic Problem, confusing the electronic system of the machine¨.
    My best recommendation is to get a New One , refurbish you must sure that the company do it, will be Good . Otherwise,
    you will the same or Worst problem.
    Thank you in advance, sincerely
    Blessing
    superchock@yandex.com
     
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