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cavitation?

Larry (from OSHA)
Larry (from OSHA) Member Posts: 727
in THE MAIN WALL
at system pressure of 20 lbs. and temp of 170*? My DHW circ (taco 009) makes a whooshing sound for a second or so a couple of times when the temp hits 170. Is it air coming out of solution or cavitation?. Do I need a certain amount of straight pipe before the circ.?

Thanks for any help.

Larry

Comments

  • Ken_8
    Ken_8 Member Posts: 1,640
    Larry,

    It appears you have an "indirect" heater?

    That you run the boiler up to 170° and at around that high limited you hear some noise?

    I suspect your suspicion of "cavitation" is correct!

    The 009 can deliver as much as 34 feet of head!

    Wrong pump!

    The relationship between the pump dynamics, the pipe size used (both with regard to length and diameter as well as fittings) and the pumps orientation within that sub-system is the area of concern.

    And yes; a straight pipe should be on the suction side of the pump. The minimum length of that pipe is typically something like five or six times the pipe diameter e.g., a 1" pipe requires a 5-6" long nipp., a 2" pipe a 10-12" nipp., etc.

    Sorry your question went unanswered for a while.

    We were all watching the Belmont or Reagan eulogies.

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  • Steve Paul
    Steve Paul Member Posts: 83
    cavitation

    What you are describing does not make any sence to me (maybe I mis-read what you wrote. You stated that your domestic hot water reaches 170 degrees, and the pressure is 20psi. If this is ths case then the temperature is way beyond the the safe limit of approx. 140 degrees and the pressure is also very low. If your numbers are correct, and the circulator is on the return side of the domestic hot water system, at 170 degrees you may be dropping the pressure to a partial vacuum and causing the water to flash to steam. That may be what you are hearing. Double check what you have told us to be sure we have the correct information.
  • Ed_13
    Ed_13 Member Posts: 164
    009 Pump on DHW???

    Larry,

    Are you saying that your 009 pump is on your Domestic Hot Water pipes that are at 20 lbs @ 170 degrees?? Please explain a bit more.
    What type of system do you have?

    Edward A. (Ed) Carey
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 727
    Ken

    Thanks for your response. You deciphered my question correctly. Yes it is an indirect tank. I don't think the 009 is the wrong pump though. The tank is a Bradford-White PowerCor, which has an incredibly high head HX. (Had I known then what I know now, I probably would have gone with a SuperStor. Oh well) Shortly after the tank was installed, I spoke with a tech at BW. He said that the pressure drop through the HX was about 25 feet and that they specified the 009 pump as the one to use. On the suction side I've got about 7 inches straight length of 3/4". Take a look at the attached pics and as always, any comments are appreciated (except please try and hold off on saying anything about the wires!!!)

    Larry
  • hr
    hr Member Posts: 6,106
    I'm not sure

    your piping arrangment is ideal. What happens as zone valves open? Does the boiler have a pump, also? is this PS piping. Draw an exact piping layout, and post it, for us to help you with.

    Can't see enough from your pics.

    hot rod

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  • J.C.A._3
    J.C.A._3 Member Posts: 2,980
    H.R.

    Looks to me like there is a pump, and a zone valve. With the 3/4 piping to the coil, my guess is that the pump is WAY overkill, and a P/S and the zone vale with a SMALLER pump would suffice.

    Maybe I missed something in the photos? Chris
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 727
    system diagram

    Thank you for your polite inference that my piping may not be "ideal". Originally, it was 3 zones of baseboard. I had the indirect added in December. The installer piped it as an additional zone. The system 007 didn't provide enough flow for a reasonable recovery. The 009 was installed to replace the zone valve and the zone valve was reinstalled on the return side to deal with ghost flow. Control is from a Honeywell AQ475A reset controller. Works great, But I'd like it work really well for a long time. I've considered zoning with circs for all zones, but it does seem like overkill. Thank you much for your perspectives.

    Larry
  • hr
    hr Member Posts: 6,106
    Consider

    Figure 6 in this article shows my favorite indirect tie in.
    Your heat zones could be taken off the primary loop.

    This method jams all the boiler output into the tank on a priority call, in the shortest possible route. Keeps different sized pumps in harmony, and handles all those nasty ghost problems. Also reduces unecessary heating of all that piping in summer DHW production mode.


    http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,93242,00.html

    hot rod

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  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 727
    hot rod

    Thanks for the reply. The parallel setup looks like a good way to go. Am I understanding you correctly that it would be OK to run my 3 baseboard zones as zone valved series circuits as part of a primary loop, (sort of like it is now) or as secondary as exactly shown in the article? Also, should I ditch my compression tank and go to an expansion tank and spirovent setup? The attached diagram is from the aq475 literature and seems to be similar to what you suggest. Also, what pipe size would you suggest?

    Thank you for your time and help.

    Larry
  • hr
    hr Member Posts: 6,106
    Depends on how much

    repiping you want to commit to. In your drawing you would want to be sure to power down the heating circ and ZVs when the larger 009 kicks in for DHW. Those two mismatched pumps will not get along running together, UNLESS you separate them hydrauliclly. Which is the primary goal of PS piping.

    Grab some of Dan's books to get a better grasp on how and why PS piping gets sized and applied. "Pumping Away" and "Primary Secondary Made Easy" are must haves.

    Looks like a good sale is currently going on at the main page :) Load up on some of this book knowledge!

    Pipe gets sized by the amount of BTU you need to pass through, and the delta t. Generally 20° delta t is used for sizing piping in an application like yours.

    You are correct in having to pump the bejeez out of those Powercors to get them to produce anything near the published output. If you stay with the PC keep the large pump, and teach the whole system to get along regardless of the mode it is in ie heating or DHW production.

    Too bad the graphs don't appear with this link, it better explains the concept.


    http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,3682,00.html


    hot rod

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