Reply To: Ventuiri effect on waterheater

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Avatar photoSylvanLMP

    Harold Kestenholz wrote on 23 December 2000 at 07:44 PM:
    Sylvan, you are right about that. One wonders why anyone would install a check valve, or other devices like a pressure reducing valve or backflow preventer on a plumbing system without installing an expansion tank on the ‘pressure vessel’ side of it Answer. Cause they are DUMMIES who never bothered to READ codes or bothered to ask WHY..they see some stumblebum do it and the apprentice thinks its right.

    After all, when you put a backflow preventer on a plumbing system, therefore isolating it from the water mains, you are making the entire system a pressure vessel.

    Including the fact that the T&P is rated to discharge @ 150 PSI and the normal rating of “plumbing” fittings is rated at 125 PSI whats wrong with this picture?

    To do so without giving the water someplace to expand, you are just asking for excessive pressure in that system.
    Although there is some air in the incoming water (about 5% by volume) and the water will expand about 3% through heating it from 50 to 120F, this is not enough safety.

    Exactly.. Also as the temperature increases so does the pressure.
    The problem is most piping guys THINK like “plumbers” and should try to learn the basics of heating to get an idea of whats happening in the hot water sections of “plumbing” A whole new science awaits them.

    After heating water, some of the bubbles leave the water. This can be evidenced by the spurting and release of air upon opening some taps.

    BUT these “taps” are well above the sensor of the T&P valve and thus the pressure can rise without this T&P even knowing it PLUS it can FLASH into steam if the temperature is high enough. It does happen unfortunately and there is no valid reason it should occur

    So the whole ‘pressurized vessel’ of the water system bottled up by a backflow preventer can then cause an excessive pressure as the heated water expands into the cold water side as well. , YES

    How many folks actually test or inspect the combination temperature pressure valves as directed by ASME?

    INSTALL and forget is the name of this game.
    At least boiler guys have common sense and common decency to test safety and relief valves monthly if not more often during the heating season. But then again MOST licensed Heating professionals CAN READ and comprehend gas fitting and heating codes.

    So every time you install a backflow preventer, double check, or pressure reducing valve separating the domestic system from the main you are creating a possible problem that the T&P valve has to handle alone, unless you add an expansion valve.

    Ever see a “plumber” bother to install a compound gauge to know exactly what is going on in the system?

    As a stationary engineer and heating guy I learned a long time ago to know what my delta is especially dealing with pressure and temperature relationships, most stumble bums could careless about thermo stress to pressure vessels and piping

    Adding another check before the water heater after already causing an isolation with a backflow preventer simply isolates the problem expansion to the hot water side, which should have an expansion space to prevent lifting the T&P as the water is heated.

    This is, after all, the purpose of an expansion tank in a modern hot water system, which is always a sealed system isolated from the cold water system by a pressure reducing valve, check valve, or backflow preventer, unless it is totally isolated by hose fill.

    Harold you ht the nail on the head the aprenticeship training seems to be lacking in several areas.

    The plumbing publications I have read lately deal with how to price a plumbing job and commissions BUT very little written about codes or WHY we have to install devices for vacuum and pressure protection.
    Harold always a pleasure talking to a real professional.. Thank you again and have a GREAT healthy holiday.. Sylvan

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