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  • New item to me.

    Well ive been doing plumbing for about 10 years now and was certified epa 608 universal back in 1997. Problem is i know how to do super heats on the old orifice units. But i have no idea what i need for a chart for the units with TXV valves. Anyone able to put up a link to some charts for superheat for these units ?

  • #2
    Re: New item to me.

    try Heating Help. ask questions (the wall). breid.....................

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    • #3
      Re: New item to me.

      here are a few pages that may help,
      HVAC/R Thermostatic Expansion Valve (Constant Superheat Valve)
      HVAC/R Everything You Need To Know About TX Valves
      sporlan has a lot of down loadable info on TVX valves,
      Sporlan - Parker
      if that link does not work try this one, and go to the approperate section,
      Literature - Parker

      take a look at quick tip 11
      http://www.parker.com/literature/Spo...nous/5-220.pdf


      here are a few down loadable manuals, (general AC and refergeration manuals),

      MEGAUPLOAD - The leading online storage and file delivery service

      MEGAUPLOAD - The leading online storage and file delivery service

      MEGAUPLOAD - The leading online storage and file delivery service

      MEGAUPLOAD - The leading online storage and file delivery service
      Last edited by BHD; 06-02-2011, 12:40 AM.
      Push sticks/blocks Save Fingers
      ~~~~~~~~~~~~~~~~~~~
      "The true measure of a man is how he treats someone who can do him absolutely no good."
      attributed to Samuel Johnson
      ~~~~~~~~~~~~~~~~~~~
      PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

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      • #4
        Re: New item to me.

        Thank you Gents the links helped a ton!

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        • #5
          Re: New item to me.

          Originally posted by mtburdick View Post
          Well ive been doing plumbing for about 10 years now and was certified epa 608 universal back in 1997. Problem is i know how to do super heats on the old orifice units. But i have no idea what i need for a chart for the units with TXV valves. Anyone able to put up a link to some charts for superheat for these units ?

          dont charge a txv on super heat....use subcool instead.

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          • #6
            Re: New item to me.

            Here is a nice reference as well...


            Refrigeration Technologies: Knowledge Center: Charing Residential AC

            Comment


            • #7
              Re: New item to me.

              Originally posted by lovetheUSA View Post
              dont charge a txv on super heat....use subcool instead.
              You're correct, but on a system with an adjustable TXV and sight glass you set the superheat.

              James

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              • #8
                Re: New item to me.

                Originally posted by James P View Post
                You're correct, but on a system with an adjustable TXV and sight glass you set the superheat.

                James
                What does a sight glass have to do with anything?

                Comment


                • #9
                  Re: New item to me.

                  Originally posted by OkieBill View Post
                  What does a sight glass have to do with anything?
                  in the old days that was how you would determine the charge of the system, bubbles in the sight glass, add some until it clear up, and just a tad more, and a very easy way to do it, all the systems I have seen with sight glass on them also have an accumulator/receiver in the system, and the TXV.
                  then you adjust the super heat, so the system does not liquid slug the compressor,

                  my two walkings have sight glass, and the old ford cars did to, very simple to properly charge,
                  one of the problems to day is with the mixed refrigerants you have a harder time not having some bubbles in the line, so there not as reliable as they once were, with the R12, R22 and R502,


                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

                  Superheat and Slugging
                  There is another very common type of metering device called a TX Valve. It's full name is Thermostatic Expansion Valve, and you will be thankful to know that its' short form is TXV. (It can also be called TEV) This valve has the additional capability of modulating the refrigerant flow. This is a nice feature because if the load on the evaporator changes the valve can respond to the change and increase or decrease the flow accordingly. The next graphic shows this type of metering device and you will note that another component has been added along with it.


                  The TXV has a sensing bulb attached to the outlet of the evaporator. This bulb senses the suction line temperature and sends a signal to the TXV allowing it to adjust the flow rate. This is important because if not all the refrigerant in the evaporator changes state into a gas, there would be liquid refrigerant content returning down the suction line to the compressor. That could be disastrous to the compressor. A liquid can not be compressed and if a compressor tries to compress a liquid something is going to break and it's not going to be the liquid. The compressor can suffer catastrophic mechanical damage. This unwanted situation is called liquid slugging. The flow rate through a TXV is set so that not only is all the liquid hopefully changed to a gas, but there is an additional 10 ºF safety margin to insure that all the liquid is changed to a gas. This is called Superheat. At a given temperature any liquid and vapour combination will always be at a specific pressure. There are charts of this relationship called PT Charts which stands for Pressure/Temperature Chart. If all the liquid droplets in an evaporator have changed state into a gas, and they still have 1/4 of the evaporator remaining to travel through, this gas will pick up more heat from the load being imposed on the evaporator and even though it is at the same pressure, it will become hotter than the PT Chart says it should be. This heat increase over and above the normal PT relationship is called superheat. It can only take place when there is no liquid in the immediate area and this phenomena is used to create an insurance policy of sorts. Usually TXV's are set to maintain 10 ºF of superheat and by definition that means that the gas returning to the compressor is several degrees away from the risk of having any liquid content. A compressor is a vapour compression pump and must not attempt to compress liquid.
                  That extra component that got added in along with the TX Valve is called a receiver. When the TXV reduces the flow there has to be somewhere for the unneeded refrigerant to go and the receiver is it. Note that there is a dip tube in the outlet side to insure that liquid is what is fed into the liquid line. Liquid must be provided to the TXV not a mixture of liquid and gas. The basic premise is to change a liquid to a gas so you don't want to waste any of the evaporator's capacity by injecting useless vapour into it. The line that comes from the condenser and goes to the receiver is also given a name. It's called the condensate line.

                  Accessories
                  Even though there are only 4 basic components to a refrigeration system there are numerous accessories that can be added. The next graphic shows a liquid line filter and a sight glass. The filter catches unwanted particles such as welding slag, copper chips and other unwanted debris and keeps it from clogging up important devices such as TX Valves. It has another function as well. It contains a desiccant which can absorbs a minute quantity of water. (a mere drop or two) Hopefully a proper evacuation removed all the air and moisture content during the installation of the equipment.
                  The sight glass is a viewing window which allows a mechanic to see if a full column of liquid refrigerant is present in the liquid line.
                  Pg 2 Refrigeration Basics
                  Attachment

                  then you set the TXV to fully charge the evaporator, at operational tempatures,
                  Attached Files
                  Push sticks/blocks Save Fingers
                  ~~~~~~~~~~~~~~~~~~~
                  "The true measure of a man is how he treats someone who can do him absolutely no good."
                  attributed to Samuel Johnson
                  ~~~~~~~~~~~~~~~~~~~
                  PUBLIC NOTICE: Due to recent budget cuts, the rising cost of electricity, gas, and oil...plus the current state of the economy............the light at the end of the tunnel, has been turned off.

                  Comment


                  • #10
                    Re: New item to me.

                    I was just giving James P a hard time... My point being that an Adjustable TXV and a sight glass do not go hand in hand ( I don't need a sight glass to adjust a TXV). Unfortunately, the sight glass while being useful in its day is about as useful as charging by amp clamp in this day and age.

                    Seriously though, If you don't also have a receiver and use a TXV chances are you will always see flash in your glass so I just got out of the habit of trusting them for anything except the moisture indicator dot on Sporlan models

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                    • #11
                      Re: New item to me.

                      Weigh the charge in and you will be spot on every time.
                      sigpic

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                      • #12
                        Re: New item to me.

                        Not True, The data plate is a starting point on A/C and Refer systems as line set length will add to your charge. Only time you can trust the plate IMO is on closed pre-engineered systems (Package units and Ice Machines)

                        Especially in commercial where you can have some very long liquid lines and older systems that were built using individual components and assembled with old school craftsmanship.

                        If you learn how to charge a system you never need a data plate (though they do give a starting point if you can find one that you can read)
                        Last edited by OkieBill; 06-07-2011, 11:14 PM.

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