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Why do we keep losing flow switches?

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[Deleted User]
[Deleted User] Posts: 0
in THE MAIN WALL
the Johnson F61KB Float Switch. On 2", works down to 13.7 gpm flow.

We don't use copper tees w/ adapters on the switch tee. Try to keep the switch connection as close as possible to the pipe. Paddle flex can be a pain.

Comments

  • Dave_118
    Dave_118 Member Posts: 17
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    Why do we keep losing flow switches?

    We have a hot water he4ating system with a flow switch in our main loop that goes between our low mass boiler and an Ergomax reverse indirect storage tank. The pump in this loop is a Taco 0010. Last March we had no heat and found out that our McDonnell Miller flow switch was not tripping. I believe it was the FS8. I replaced it with another one, and we were fine until tonight when we came home and again had no heat. I twisted the wires from the switch together, and we again have heat. Why would be losing 2 switches in 8 months? The water is a 30% glycol mix. Everything else seems fine. The switch is in a striaght run of 2" copper pipe on the outflow of the boiler. The paddle looks plenty long enough. Would there be some better switch to use? Thanks.
    Dave
  • Unknown
    Unknown
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    Alzhiemers?,

    are you sure the paddle size is correct?, and perhaps something is eating it away (over time) to prevent its proper flow.

    Dave
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    alternative

    Try a pressure differential switch. Could be easily isolated from the system and changed without a drain down and is not obstructing flow. See attachment

    What is the purpose of the switch in your system?

  • Paul Rohrs_7
    Paul Rohrs_7 Member Posts: 173
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    Bold

    Glenn, it's pretty bold to post that PDF document, you may consider removing that. Be mindful that this is Dan's site and he respectfully requests that pricing be kept off of the site. There are plenty of channels via private email for discussions of price. Your vendor might not be to pleased to have their pricing splashed around the web either.

    Will boiler inspectors accept these pressure differential switches in lieu of flow-switches?

    Paul
  • Dave_118
    Dave_118 Member Posts: 17
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    The switch is

    used as a safety...in case there is no flow in the main loop (pump failure, etc), the boiler will not fire.
  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    your right

    I didn't realize the quote was attached to the pdf spec. I understand, agree, and try to abide by concept of no pricing. Not intentional. This was a job quote. Actually pretty stupid of me, not bold. I have 2 different laptops, can't access the edit tab to remove it using either one. Not sure why, but again, my apologies, it was not intentional.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    The fix...

    If you've ever noticed, on the larger CFT type of boilers that require a flow switch as a part of their CSD! controls scheme, the flow switch is installed at a slight angle to the flow. This way, the paddles only sees a portion of the oncoming flow of fluid. Less paddle stress = longer paddle life expectancy.

    BTWm did you ever contemplate what happens to the missing paddle segments?

    Sometimes, you get lucky and they lay down in a header and are benign. Sometimes, they get caught at a tube inlet and cause that tube to fail early, and sometimes they get caught in the impeller of the pump, causing problems for ALL the tubes due to decreased water flows.

    Unlike missing socks in your laundry, these DO come back to haunt you...

    Try cocking it at about a 45 degree angle to the flow and see what happens...

    ME

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  • Glenn Sossin_2
    Glenn Sossin_2 Member Posts: 592
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    affect tripping

    Mark

    Won't that have a significant effect on tripping the switch?
  • Dave Stroman
    Dave Stroman Member Posts: 765
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    I have found that most of the problems I have with flow switches is not enough flow. And sometimes the older they get, the stiffer they get. You could use a bigger pump or reduce the pipe size before and after the switch.

    Dave Stroman, Denver

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  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,572
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    I beleive if you read the McDonnell Miller instructions you need a minimum velocity in the pipe to trigger the switch.

    I had one installed in some chilled water piping that was oversized for the flow. The switch would not work. Downsizing a section of the pipe fixed it.

    Worth looking into.

    ED
  • [Deleted User]
    [Deleted User] Posts: 0
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    Paramters needed...

    THe FS4-1 does have its limitations. Not more than 10 feet per second. What kind of flow do you think you are acheiving?

    For example, a T/L CFT 5,000,000 btuH boiler has a flow rate of 333 GPM through the HXer to get a 30 degree rise. If memory serves me correctly, the inlet and outlet of the HH500 is three inch. If that is the case, the water is moving through that section at 15 feet per second, hence snapped flow switch paddles.

    Check your velocities, and if need be cant the flow switch to releive the stress of swimming up stream..

    Good info online for the FS is at http://www.bellgossett.com/literature/files/1470.pdf

    ME
  • [Deleted User]
    [Deleted User] Posts: 0
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    If he's snapping off flow switch paddles...

    I seriously doubt that it will be a low flow condition, probably the opposite. The flow switches do have a sensitivity adjustment on them for lower flow rates. Also, when properly piped and used, the flow switch SHOULD be seeing a constant flow, not a variable flow condition.

    ME
  • Dave_118
    Dave_118 Member Posts: 17
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    Mark,

    I think you're right.....we are probably losing the switches because of the higher flow. When the pump comes on, it is jarring the switch, and they only last about 8 months. This is what I did.....
    We had an old Potter ISF-1 switch from a previous incarnation of our system. It had lasted 4 years before we had our system repiped (problems with noise in low mass boiler). That switch handled flow from a Taco 0012 pump. The paddle was somewhat shorter, so I put that in figuring there would be less surface area getting slammed by the flow. I then adjusted the sensitivity so that the switch closes with flow but opens as soon as the pump is disconnected. Everything is currently working fine. Would it make better sense to put in the longer paddle (for 2" pipe) and turn switch 45 degrees or leave everything as is for now?
    We never lost any paddles. Just the switches stopped operating.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    My bad assumption...

    I've had more broken paddles then non operating switches, so I automatically ASSumed the broken paddle scenario... My bad.

    You can achieve the same goal either way, but if you leave the paddles longer, make sure you use the "spare paddles sent along to give your paddles more stiffness. And, make sure the paddles don't bottom out in your tappings. Personally, I think it is better to have more exposure than needed and adjust the angle to that, as opposed to running on the lower end of the switches capacity, but that is just my experience and opinion. Nuisance trip outs like yours are a pain to adjust to with the sensitivity adjustments.

    ME

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  • Dave_118
    Dave_118 Member Posts: 17
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    Thanks. I'm wondering what would be the appropriate switch to use for our flow. We have a Taco 0010 pump which can pump up to 30 gpm. The boiler has a very low pressure drop (copper tube), and the pump circulates water from the boiler to an Ergomax 65 gallon tank and back to the boiler in 2" copper pipe.We have approximately 30% glycol mixture. Total piping is approx 25-30 feet. Would the Potter IFS1 be an appropriate switch? I have a hard time reading the specs. Also, if I wanted to put in the longer paddle, could I use the one from the Mcdonnell Miller switch as we do not have anything from the original switch). It is reinforced with a smaller paddle behind it).
    Thanks.
    Dave
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Actual flow specifications required...

    That is the only way to know for sure if you've chosen the right switch. Just because the pump is "capable" of moving a certain volume of water doesn't mean it is. If you can give us a diagram of your system configuration, including pipe lengths, fittings, valves etc, we can calculate exactly what you SHOULD and WOULD be moving, and then you can choose the proper flow switch.

    As an alternative, if you know for sure (clocked meter) what the input of your appliance is, and have confirmed combustion efficiency (% output) and can tell us what the differential in temperature is across the heat exchanger, we can tell you what the flow rate is based on that data. You might be sur prised at what you may find...or not.

    ME

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  • Dave_118
    Dave_118 Member Posts: 17
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    Based on the info

    from our boiler manufacturer, we have a max flow between 20-25 gpm (since we have a 20 degree delta T across heat exchanger based on our temp gauges). The boiler is a Lochinvar EBN 300 (300K BTU).
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    I calculate 24 GPM...

    Assuming approximately 80% thermal efficiency.

    What pipe size (velocity) is the FS connected to?

    ME

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  • Dave_118
    Dave_118 Member Posts: 17
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    2\" copper

  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Low velocity is the issue...

    Remember, water is like my ex-brother in law. Wet, lazy and stupid...Hence, EX brother in law...

    But that is besides the point. At 24 Guppies Per Minutia (isn't that what GPM stands for?) the 2" pipe will have a velocity of 2.5 feet per second. THe flow switch (MMFS4-1) is rated for 2 foot per second MINIMUM, or 3.45 F.P.S.maximum on 2" pipe..

    With that being the case, if you decrease the pipe size just before and after the flow switch to 1-1/2", you will be more towards the upper end of the flow switch's capability, and have less potential for nuisance drop outs...

    Whew, what a ride :-)

    ME

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  • Dave_61
    Dave_61 Member Posts: 309
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    Is there any switch that I can replace it with that

    would be OK with the current flow velocity? Otherwise it involves cutting/soldering....something I am not comfortable with.
  • realolman
    realolman Member Posts: 513
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    I think

    that measuring flow in general is a often a more difficult proposition than a person would initially think.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    The problem is the technology at hand...

    A paddle switch is a paddle switch, and they work on the same principle regardless of the manufacturer. They all have to fit their paddle into a very small hole, which in turn makes for a rather small target.

    Find a local plumber who has the ability to do pro press and you can be done in an hour.

    ME

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  • Dave_61
    Dave_61 Member Posts: 309
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    What would be the length of

    piping on either side of the flow switch that would need to be decreased from 2" to 1.5" to increase the velocity?
  • Dave_61
    Dave_61 Member Posts: 309
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    How about the Potter IFS-1?

    This is the one I used to replace the existing switch, but I'm not sure by the attached specs what the min flow would be in 2".

    http://source.invensysibs.com/ps3pdf/Section7/IFS.PDF

    They talk about flow increase and decrease. Can anyone decipher this?
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    5 X pipe diameter

    Installation instructions ca be found at

    http://www.bellgossett.com/literature/files/1470.pdf

    ME

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  • Dave_61
    Dave_61 Member Posts: 309
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    Mark, thisorry to keep beating a seriously injured horse, but

    this is the switch currently in place with smaller paddle. It looks like the minimum flow is definitely within our range and looks like it would be in the higher range of the switch's requirements...with the 2" pipe.

    http://source.invensysibs.com/ps3pdf/Section7/IFS.PDF

    Does that make sense or am I reading it wrong?





  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Try adjusting it...

    THere is an adjustment screw on it for flow sensitivity. Just make darned sure you do a no flow drop out test on it after adjustment, or you may find out what the low mass dance looks like, and your sphincter may learn how to do the momba....

    Follow the manufacturers instructions (available on line).

    ME

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  • Dave_61
    Dave_61 Member Posts: 309
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    I did....I adjusted it so that it

    closed on flow and gave it a little extra leeway. I then disconnected power to the pump several times, and each time the boiler shut off. Does it seem like this should work without repiping?
  • [Deleted User]
    [Deleted User] Posts: 0
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    Only one way to find out...

    Let 'er rip!

    ME
This discussion has been closed.

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