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Thread: Newbie can't quite understand-Pressure switch cut-out

  1. #1

    Default Newbie can't quite understand-Pressure switch cut-out

    Newbie can't quite understand-Pressure switch cut-out


    Hi there,
    Trying to get the my water to stay on and the Square D switch just keeps giving me fits. System has just been replaced (by me) with all new Pressure tank. !00 PSI tank with HT30 designation, (50% larger that I had before) I have replaced all fittings including the inlet nip and and Pressure tank tree etc. There is a check valve in the pump line ( out near the well head) which is 75 feet away. Well is a 180 feet deep with a 220 Volt system (1.5HP?) and is feeding downhill from wellhead to entry point to house. It's 1" Plastic pipe from 10 feet below surface to basement entry point. The system feeds a single family dweliing with very condensed piping system with 2 middle aged adults. I have installed on demand water heater (Bosch) so no Hot storage in system. I have replaced all pipe at the new pressure tank including 1/4 inch feed to the pressure switch, a SQUARE D FSG2J20M4CP Universal pressure switch. it has provision for low pressure cut-off. It has two separate adjustment screws. One for Cut IN (Adjust nut down for higher cut-in pressure) and one for cut-out, Turn nut down of higher cut out pressure. I can get it to pump up to 45 PSI with no problem, and it will produce plenty of pressure for the system. (I do have a pressure gauge (new) that gives me good readings)
    MY PROBLEM is..when something of low volume usage like the washing machine, the water softner, or sometimes a toilet is being used, it seems to just drain pressure ever so slowly down to about 35 PSI and then the whole bloody mess dumps out and I have no water pressure at all. ZERO. It will not reset (This presssure swiutch has the reset lever on it) automatically, and so you have to run down and manually jump the system again.
    Thsi is a real bummer. I have tried a variety of settings, but I can't seem to get the right combo..and It's really starting to get to me.
    Notes: 1There is no check valve at the pressure tank/water inlet to the house, but there wasn't one on the old one either. I did notice that we get a little surge in the shower that is noticable, but it does no getnerally cut out. It's a low flow problem.
    I am hoping I jsut have missed something witht he switch setting..but this getting ridiculous. The sytem was replaced because of a bladder leak in the old tank that had the old pump cutting in and out way too often, and I was afraid of burning it up. (It's a Red Jacket-1.5 years old, the one prior to that went 15 years). So...the Classic...there I made the thing all new, and twice as big, with better components, and now it works have as good AAAAARRRGGGHHH Help me please.
    Mr. Phunn1.

  2. #2
    DIY Senior Member Hube's Avatar
    Join Date
    Sep 2004


    What is the air pressure in the tank,when empty ?

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default pressure

    While you are drawing water the air pressure in the tank is expanding the "balloon" inside the tank, (as the water pressure squeezing it is dropping), and pushs water out. This keeps continues until such time as the water pressure equals the air pressure charge in the tank. At that point the balloon fills the tank and there is no more water to push out, so the pressure drops to zero immediately. You have a pressure switch problem of some kind.

  4. #4

    Default pressure readings

    Thanks for the replies. The tank is a H2-OW-TO Brand, HT30 part designation and the pre-charge pressure is 28 PSI., Beginning to feel kinda stupid here. I have have a 20/40 switch. Does that mean I have to bleed this thing down to about 18 PSI to get the proper cut in or cut out. I could really stand some better pressure here, should I just get a 30-50 switch and that would settle that and let me maintain the pressure. Or...can I adjust this swith up to the higher bladder/tank pressure?

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Note, I'm not a pro. If your pump and well volume will support a higher pressure, you could adjust the switch. Otherwise, yes, you should drop the pressure of the tank to match your current setup. What happens now is that the water pressure will drop from the max to 28 gradually as the bladder expands, then fall to zero turning on the pump giving you a momentary hiccup (even though the tank has 28# in it, it can't push against anything since you've run the water out of the system, thus no water pressure). With the pressure in the tank set to 18 pounds or so, it is still holding water when the pump triggers, and no hiccup as the pressure drops to 20, the pump turns on and trys to build it back up again.
    Last edited by jadnashua; 03-11-2005 at 09:06 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6

    Default Thanks on switch gig

    Thanks for the answeres and tips. I dropped the water ouot of the system, dropped the pressure in tank from 38lbs to 24lbs and turned up the cut in pressure spring so that it would cut in at higher than the 20 lbs factory set. It's hummming right along as designed,cutting in at about 30psi and steady pressure , smooth cut-ins and all. still seems to run best at about 35psi pump pressure and everything in the system can keep up with it. So...thanks for helping me out...Now it's clear to me conceptually. I was struggoling with the concept.



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