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Thread: Flow switch for dry running protection

  1. #16
    DIY Member MarkHash's Avatar
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    Yer right I definitely lost you. I think you gotta be pullin my leg about the wall switch!

  2. #17
    DIY Member MarkHash's Avatar
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    I read your post once more.......in my scheme of things, and I could be way off, your pressure switch would have 12 volts wired to it instead of 120 volt motor voltage. When the pressure switch is at it's low cut-in it sends 12 volts to both the flow switch and the timer module. The outputs of both the timer module and the flow switch are connected to the relay (contactor) that controls the pump. No electrical current is passing through the flow switch yet but the timer module has a direct connection to the pump relay. This starts the pump. The flow starts and now the flow switch is conducting electrical current and voltage to the pump relay. The timer contacts disengage after a few seconds but the pump keeps running until the flow switch opens the circuit in a no flow situation. This is called a latch circuit. On the supply side when the pressure builds up again (I am assuming this pressure is supplied from elsewhere) the whole thing starts over again, without you having to GO TO THE WALL SWITCH.

  3. #18
    DIY Member MarkHash's Avatar
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    very simple diagram
    Attached Images Attached Images  

  4. #19
    DIY Senior Member Bob1000's Avatar
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    That makes sense now , thank you !

    However I got some questions

    How reliable is that electronic components?

    Do you think that that stage of the timer kicking in the pump for the flow switch to contact is necessary?
    Wouldn't the city water flow move its arm when you open a faucet ( of course assuming that there is a reasonable flow there ) .

    Let me assume the following case :-

    Flow switch cuts off the circle because there is no water in the city supply side , the pressure switch is still in the cut in position and that would make the timer kiks in the pump at the designed intervals but process would not continue cos the flow switch would not contact
    The pump would then cycle untill the city water is back and the pump can complete its operation circle
    Assume the city water is cut for some hours , what would be the case?

    I think the timer would need a long programme
    Last edited by Bob1000; 04-01-2008 at 04:41 PM.

  5. #20
    DIY Member MarkHash's Avatar
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    Yeah I haven't thought about your whole scenario. The timer powers up, drops off at the thumbwheel programmed time, and will not trip again until power has been interrupted to it. So the pressure would have to build up to cut-off before the timer could cycle again. If flow stops from lack of water to the booster pump, the pressure switch is still calling for the pump, but the relay remains open until city flow is restored enough to operate the pump via the flow switch. I wonder if a 2nd timer on the flow switch output side would be needed here to prevent too many starts and stops of the pump if the city pressure is fluctuating near the on/off threshold of the flow switch (to act as a dampener)? It probably depends on if the flow switch has similar curve characteristics of a pressures switch that would prevent that. If the pressure reaches the cut-off setting then the booster pump stops since the flow has stopped, interrupting the electrical path thru the flow switch to energize the pump relay. Now when you operate a faucet, if the pressure switch is still at or below cut-in, yes the booster pump will come on. Is this a problem?
    As far as the ct-70 timers go, I have some that are still working in alarm panels after 20 years! They were used on older alarms to engage entry delay shunts for motion detectors looking at entry doors so they have gotten quite the workout too. This has been interesting, I am curious how they have solved this in all-in-one pump protection products. I am not crazy about the hot-stop idea, seems like it would be hard on the pump but I really have no experience. I know that with a plc micro you can try different timing scenarios and monitor the whole process on your laptop screen while it's operating. Once it's tuned in you disconnect and just let it run. I have two of the Amtrol booster pump and tank setups I got on E_bay, an RP-10HP and an
    RP-15HP, not sure if I will use them but they were both steal deals.

  6. #21
    In the Trades Bob NH's Avatar
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    You could do it with a reverse action pressure switch and a time-delay relay.

    Install a pressure switch on the suction of the pump that will open when the pressure drops below the point where you want to operate the pump. Reverse action pressure switches are available from different sources. For example, The FRG52 (links below) can be set to a cut-out pressure (switch opens) as low as 1 psi and a cut-in pressure of 6 psi. The FRG32 has a cut-out pressure as low as 4 psi and a cut-in pressure adjustable from 6 to 20 psi above the cut-out pressure.

    http://ecatalog.squared.com/catalog/.../17320014.html

    http://ecatalog.squared.com/catalog/...f/17320014.pdf

    Then install an On-delay relay such as the SSAC TRU Series using the "Delay on make" function where the output contact is closed at a set time up to 1000 minutes (16.67 hours) after voltage is applied.
    http://www.ssac.com/standard/ff-tdr1.htm

    http://www.ssac.com/catalog/TRU01A01.pdf

    When the pressure drops below the set pressure (for example the 1 psi setting of the FRG52) the power is removed from the relay and the pump stops. If the pressure dropped because the pump was drawing water, then the pressure might be immediaely restored, applying power to the relay. However, the relay contact would not close until the delay setting had elapsed.

    For example, it would be possible to set the delay for one hour, in which case the system would "try again" every hour to see if there is anough water to supply the pump.
    Last edited by Bob NH; 04-02-2008 at 05:57 AM. Reason: Typo correction

  7. #22
    DIY Senior Member Bob1000's Avatar
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    Please have a look to the flow switch link below
    http://www.watts.com/pro/_productsFu...?pid=685&ref=1

    I think kiking in the pump by a timer activated by the pressure switch is a must because if you wait till the flow switch paddel get pushed by the flowing water you must wait till the city pressure is able to flow to the pump inlet and that would not happen at the cut in pressure of the pressure switch if it is greater than the city pressure ( most of the cases it is bigger) otherwise you would open a faucet and wait till the pressure tank empties ALL its water capacity then the pressure is less than the city pressure for the flow switch to kick in .

    A second timer would be needed as well to stop cycling at the city pressure near to flow switch pressure threshold

    I do agree with you that the Thermal sensor is a bad idea because the pump would be toast before it cuts out

    I am thinking of another idea ..
    The new pump would be able to deliver 87 PSI sucking from a bucket of water without any need for city pressure just if the water is just present at the pump inlet , so I am thinking of fixing a sensor that would sense the presence of water in stead of the flow switch

    Any comments?

  8. #23
    Moderator valveman's Avatar
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    There will still be water in the lines, it will just be at 0 pressure. A loss of prime or reverse acting pressure switch would be the simplest. If you give it a wide bandwidth, such as off at 20 and on at 40, it should not bounce the pump as the pressure in the city line increases.

  9. #24
    DIY Member MarkHash's Avatar
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    I agree that the octal base plug-in timers would be the better choice here. Good luck and let us know how it works out.

  10. #25
    DIY Senior Member Bob1000's Avatar
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    Quote Originally Posted by valveman View Post
    There will still be water in the lines, it will just be at 0 pressure. A loss of prime or reverse acting pressure switch would be the simplest. If you give it a wide bandwidth, such as off at 20 and on at 40, it should not bounce the pump as the pressure in the city line increases.

    I know that the reverse acting pressure switch would be the best and simplist but I can not find it in the local market here as they only sell the Square D normal one no the reverse action one , it seem that no body would be interested in it lol

    I will go to some HVAC shops and try to find something similar that can do the job

    I think a low pressure cut out with automatic reset would do the job

  11. #26
    Sprinkler Guy Wet_Boots's Avatar
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    One can always connect a relay to a pressure switch and turn the DPST action into DPDT action.

  12. #27
    DIY Senior Member Bob1000's Avatar
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    Quote Originally Posted by Wet_Boots View Post
    One can always connect a relay to a pressure switch and turn the DPST action into DPDT action.

    I think I know what you mean but still the min pressures values that the nomal pressure switch is designed for are much higher than the rates I would be looking for because I would be looking for a 5 psi threshold ( Cut out) or even less because the pump would suck any water in the pipes and can give 87 psi at the other end

    Will search for an HVAC one with an automatic reset and advise back

  13. #28
    In the Trades Bob NH's Avatar
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    There are lots of solutions; many of which have been suggested here. I suggest that you pick one and implement it.

    First you must define your requirements to yourself.

    1. What is the lowest source pressure that will be available when the pump is drawing low flow (maybe 3 to 5 GPM) from the system?

    2. What is the required pressure range (low at pump start; high at pump shutoff)?

    Then, buy and install a pump that provides the GPM and pressure range that you need.

    A Goulds HSJ07N will deliver a shutoff pressure exceeding 70 psi at zero psi suction pressure, and it will work even if the suction pressure is 50 psi.

    At the "zero pressure suction" condition it will deliver about 15 GPM at 50 psi.

    You can set the pressure switch at 50/70 or anything else you like as long as the shutoff pressure is 70 psi or less.

    You must have a relief valve set at maybe 75 to 80 psi.

    So, all you need is the pump and pressure switch that delivers what you want, and a relief valve to keep from exceeding the safe pressure limit if the pressure switch fails.

    If you want even more pressure there are pumps that will deliver what you want.

    No relays. No reverse action pressure switches. No worries about varying water pressure as long as it is greater than zero.

    If you want it fancier you can get a pump control that will automatically shut things off if the source fails completely.

  14. #29
    DIY Senior Member Bob1000's Avatar
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    Default Have city water cut offs often in summer

    Quote Originally Posted by Bob NH View Post
    There are lots of solutions; many of which have been suggested here. I suggest that you pick one and implement it.

    First you must define your requirements to yourself.

    1. What is the lowest source pressure that will be available when the pump is drawing low flow (maybe 3 to 5 GPM) from the system?

    2. What is the required pressure range (low at pump start; high at pump shutoff)?

    Then, buy and install a pump that provides the GPM and pressure range that you need.

    A Goulds HSJ07N will deliver a shutoff pressure exceeding 70 psi at zero psi suction pressure, and it will work even if the suction pressure is 50 psi.

    At the "zero pressure suction" condition it will deliver about 15 GPM at 50 psi.

    You can set the pressure switch at 50/70 or anything else you like as long as the shutoff pressure is 70 psi or less.

    You must have a relief valve set at maybe 75 to 80 psi.

    So, all you need is the pump and pressure switch that delivers what you want, and a relief valve to keep from exceeding the safe pressure limit if the pressure switch fails.

    If you want even more pressure there are pumps that will deliver what you want.

    No relays. No reverse action pressure switches. No worries about varying water pressure as long as it is greater than zero.

    If you want it fancier you can get a pump control that will automatically shut things off if the source fails completely.

    Thank you BobNH
    I have bought already a new 2HP expensive pump that I am going to install to rplace my 1HP pump that i have it running right now that is why I am keen on some sort of a suitable but simple dry run protection
    The pump I have can deliver 87 psi at zero city pressure and I will set up my pressure switch to 60/80 so now I got my cut out pressure problem solved

    I was thinking of a protection method works on either pressure or flow , from the views given here I think the most simple is the pressure switch reverse action but what I am worried about is that may be my new pump when it starts would make a sudden momentary drop of pressure at the upstream side that would make the low pressure switch opens and ut off the power specially if it is set to a low value like 1 psi for example

    any comments?

    I am planning to go buy it tomorrow so I would appreciate your comments soon

    You said if you like it fancy , there is a pump control , what is that ?
    of course I am VERY keen on having that sort of protection because in summer I always have frequent city water cut offs in the peak hours and one of them is enough to burn my new pump
    Last edited by Bob1000; 04-04-2008 at 02:34 PM.

  15. #30
    Moderator valveman's Avatar
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    A couple of years ago there was a city in Texas that had a big fire. The fire trucks were sucking on the fire hydrants faster than the city and water lines could supply. The suction collapsed the city water lines in many places. If you suck it down below 0 pressure, you can collapse your lines. A flow switch doesn't care about the pressure and could still be closed as you were creating the negative pressure. A low suction pressure switch will catch before negative pressure.

    You can give it a wide bandwidth to stop the cycling from the city pressure coming and going. Set it to shut down at 10 PSI and not back on until the city pressure gets back up to 30 or even 40 PSI. You can also install this switch with a small 1 gallon size bladder tank. If you restrict the size of the opening to this tank and switch, it makes a mechanical timer. a gallon of water has to come in or go out of this tank for the pressure to change from 10 to 30. So the slower you let this water in an out, the more time you have between off and on, and the switch does not bounce the pump on and off. I have one set up this way with a 1/4" poly line running from the main line to the little tank and switch. No switch bouncing!!

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