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Hitachi Compressor dies when unloader engaged

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  • Hitachi Compressor dies when unloader engaged

    I have a Hitachi Koki EC2510E wheelbarrow gas air compressor that starts and runs fine at idle when the unloader valve toggle is in the up bypass position (air venting) but when I put it down to fill the tanks the engine dies (it is supposed to rev up). I put in new gas, cleaned the fuel filter, took carburetor apart and cleaned, checked air filter. It has the pneumatic tube from unloader valve to engine to control engine speed. There are some adjustment screws on the engine but my manual doesn't say how to adjust them so I left them alone. Anyone got ideas on what to do next? Thanks!

  • #2
    I am not at all familiar with portable, engine-driven compressors and they're regulation and unloader systems. That said, I am wondering if the compressor is shutting down because of the unloader being switched or is it actually shutting down because the pressure transfer to the tank is causing it to be overloaded and thus it shuts down?

    In other words, the compressor is running fine as long as it is "unloaded", air pressure just exhausting with no back pressure load. But when you close the valve to transfer the pressure to the tank, the compressor can't handle the load and it shuts down (overloaded!). Normally, as you mention, when the valve transfers the pressurized air to the line going to the tank, it is apparently not making it through the line or through the 'check valve' located on the entry port to the tank. Or if it is, then the tank is already pressurized and isn't allowing air to flow.

    I presume you have checked the tanks to ensure they are pressure free and are seeing no pressure on the tank gauge. Also, have you check to make sure the pressure line from the compressor exhaust port to the 'check valve' on the tank is free from pressure, like was it properly unloaded when the compressor shuts off?

    On an electric motor-driven compressor, you would not have to "transfer", but if the check valve failed or the line between the compressor exhaust port and the check valve wasn't properly unloaded, you would get the reaction that the compressor wouldn't run because of the back pressure in that line. Sounds to me, in your case, that you have a similar problem, because once you transfer the line, the compressor may be seeing backpressure and the load is perhaps causing the shutdown. In such cases, the problem is usually in the unloader mechanism of the pressure switch, or in a failure of the check valve which allows tank pressure to bleed back into the line and/or compressor cylinder itself.

    Just a guess of course, but again, I'm not familiar with air flow regulation or transfer on an engine-driven compressor.



    • #3
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      • drainman scott
        drainman scott commented
        Editing a comment
        thought this might help