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What is PSI at max GPM?

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  • What is PSI at max GPM?

    Hi there,

    I'm considering purchasing the 3300PSI PW. One of the reasons being I have a pipe cleaning hose that has the following requirements: min. 3 gpm @ 800 psi

    I see the 3 gpm rating on the 3300PSI unit, but would anyone know what the PSI is at max GPM?

    I am new to the pressure washing tool above all, but I haven't necessarily equated max PSI means max GPM. If I am wrong let me know.

    Thanks in advance for any insights.

  • #2
    Re: What is PSI at max GPM?

    a pressure washer uses a positive displacement pump.

    what this means is the volume of water is determined by the pumps displacement, multiplied by the pumps rpms.

    pressure is developed by applying back pressure to the pumps output. hence the nozzle.

    the majority of these pressure washers are direct drive. no belts and no gear boxes to slow the pumps rpms. down from the engines rpms.

    so in your case, the engines rpms are 3600 and the pumps max output is based on the 3 cylinder pump rotating at 3600 rpms. as you put a load on the pump, when you build pressure. this slows the engine and ultimately the pump. with a properly sized pump and engine, the output volume at the rated pressure should be met.

    but remember the pump is designed for a maximum amount of water displacement. the slower the rpms, the less water. the faster, more water.

    rick.
    phoebe it is

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    • #3
      Re: What is PSI at max GPM?

      presser washers normally use a piston pump or a positive displacement pump,

      so your only going to get about 3 gallons a min out of it if there is no pressure or if you use a nozzle that restricts the pressure to 3000, if one would use a smaller nozzle to up the pressure you would probably would need more engine to turn the pump and more than likely the pump would not last as it would over stressed, (but they also use a unloader to protect the pump and motor),

      but a given pump can only pump so many gallons a min and since it is positive displacement it will pump it with resistance or with out,

      to change the gallons a min you would have to change the speed of the pump, or motors speed driving the pump,
      Push sticks/blocks Save Fingers
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      • #4
        Re: What is PSI at max GPM?

        Originally posted by PLUMBER RICK View Post
        a pressure washer uses a positive displacement pump.

        what this means is the volume of water is determined by the pumps displacement, multiplied by the pumps rpms.

        pressure is developed by applying back pressure to the pumps output. hence the nozzle.

        the majority of these pressure washers are direct drive. no belts and no gear boxes to slow the pumps rpms. down from the engines rpms.

        so in your case, the engines rpms are 3600 and the pumps max output is based on the 3 cylinder pump rotating at 3600 rpms. as you put a load on the pump, when you build pressure. this slows the engine and ultimately the pump. with a properly sized pump and engine, the output volume at the rated pressure should be met.

        but remember the pump is designed for a maximum amount of water displacement. the slower the rpms, the less water. the faster, more water.

        rick.
        All joking aside...
        Clean post Rick.It's good to have you here.

        Now,Back to reality..




        Spaz

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        • #5
          Re: What is PSI at max GPM?

          Thanks Rick and BHD for your replies.

          Given the positive displacement pump, it sounds like I will get the full rated GPM as long as the engine is operating at the full rpms (and not something I can control anyways). And the nozzle size determines the back pressure - and as long as the nozzle size does not create a pressure exceeding the PSI rating of this particular unit, then I should have a properly sized engine/pump for the job.

          Sorry if this sounds like a repetition to what you guys have said. I just needed to sound it out for myself.

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