3 Replies Latest reply on Oct 8, 2014 11:53 AM by BoBraxton

    Backflow preventor for automatic dishwashers


      We bought this house in 1984.

      Around ten (eleven?) years later, we paid to have everything removed from kitchen / den

      great room and all new appliances installed (gas stove top, upper microwave, electric convection oven,

      automatic dishwasher.

      The trouble is, over a period of a long time the drain from the automatic dishwasher to the (higher) disposal

      backs down into the pan / tub at the base of the automatic dishwasher.

      This is a quiet "European" model - Bosch as I recall.

      Any plumbers in "MyRetirement" with advice.

      Somehow I doubt that the contractor followed "Code" properly, otherwise

      how could this "backflow" be happening (again and again)?


      Backflow preventor for automatic dishwashers
      US 3929149 A





      A backflow preventor for installation in the water discharge line between an automatic dishwasher and a garbage disposer, the backflow preventor including an inlet tube for receiving water from the dishwasher, and an outlet tube for discharging water to a garbage disposer or directly to a sewage system, both tubes having upper ends forming the under side of a valve cavity having lateral antisyphon vent ports, and ball check valve retainer and guide means, the ball check valve seating on the upper end of the inlet tube, to prevent backflow to the dishwasher and movable therefrom to permit free discharge of water from the dishwasher through the antisyphon device.


        • Re: Backflow preventor for automatic dishwashers

          Back flow valve on the discharge of the dishwasher water pump may be bad, but this is a new dishwasher.  Prior to calling the dishwasher repair man make sure the discharge water line to the disposal rises above the disposal prior to entering the disposal.  Line should be long enough to do that.  Sometimes "plumbers" forget to install that loop when installing the dishwasher or even changing out the disposal.  The loop forms a trap so waste doesn't go back into the washer.  Water at the bottom of the dishwasher, (there always is some)  should be relatively clean.  If it has food particles in it, that's probably your problem.

          I'm not a plumber but had the same problem recently.  Put 2+2 together and problem started when I had a new disposal installed.  Curious how you are getting the water out of the pan.

            • Re: Backflow preventor for automatic dishwashers

              Thank you thank you

              this alone is worth "the price of admission."

              This "new" work was done around 1994 1995.

              The (discharge) water "line" is (not a "solid" pipe) sort of like an accordion

              although much smaller in diameter, sort of like the clothes dryer lint 4" or so line that leads through

              our garage wall out into the outdoors.

              I checked. That "line" is plenty long.

              The "plumber" could have put in some kind of hanger to hold it up to make the high loop.

              My understanding is that this  - makes an "air block" a section of air which prevents

              syphoninng. All I did was cut to length about 26 inches a piece of 1" x 2" (3/4 x 1 1/2) to prop up

              the line and give it a generously high loop.

              I think the disposal is what pushes the drain / dirty water down that line.

              As far as getting the water out, just running the dishwasher through normal cycle "4" setting (this is Bosch)

              drains it - plus, this taught us to clean that filter in the bottom of the dishwasher pan.

              You Tube came to our rescue (this is how you ....). Thank you, thank you - from the bottom of my automatic dishwasher.