Gravity fed water system help

Discussion in 'Pumps and Tanks Well Forum & Blog' started by extendedpath, Mar 14, 2011.

  1. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    I have a 5,500 gallon cistern that gravity feeds my house and shop / garage; they are fed with there own 2†polyethylene pipe. The water level of the cistern should only fluctuate 2 to 3 feet. The water in the cistern feeds the fire sprinklers and potable water. The house is still under construction and the shop has been in use for a few months.

    Last week my wife's car got bath from one of the sprinklers and also brought out the fire department. The sprinkler company thinks it was from water knock or a presser fluctuations in the system. We think the car wash started as my wife cut off the shower and the toilet finished filling. We have tried a few times to recreate it but no luck so far.

    There is about 115' of elevation from the cistern to the shop. The pipe run was 380'. The static water presser is 51psi. There is a 32 gallon presser tank that is precharged to 48psi. There are no check valves.

    I talked to one well driller and had no idea. Talked to a plumber and he was talking about added 2 more tanks and a check valve; but once we drew it on paper he had no idea. I started thinking it could be water osolation between the presser tank and the cistern causing a psi spike. The cheapo psi gauge dose not show much but have a better unit on order.

    I'm open to suggestions, ideas, and questions.
  2. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    Have you calibrated the two pressure gauges? I assume you are measuring the precharge on the bladder with a different gauge. It could be that the bladder is over inflated. I'd drop it a few pounds.

    Do you have hammer stops on the house lines?
  3. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    No I have not calibrated my gauges or know how to.
    I used one gauge to get the pis of the water, opened up the tank drain, turned the water on at the sink then set the tank psi. Thinking about this makes me think.

    I don't have hammer stops installed in the house or any other plumbing. I'm planning on starting the plumbing end of the week. I do plan on installing hammer stops in my house.
  4. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    If you read the air pressure when there is water pressure, they should both read the same. Since the water pressure is static, the bladder precharge would best be set 10 PSI below the average water pressure.
  5. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    That sounds good. I'll set it up like that tomorrow.
  6. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    You must have check valves on your down hill run. All the opinions on this forum against water well check valves do not apply for these conditions. I would have a few of them, but at least one GOOD one just at the bottom at the entrance to the tank is essential. You already have a hammer arrestor [helper] , the pressure tank.

    Unless your wifes shower head is a fire hose, and the toilet is for an elephant, shut off did not break your sprinkler head. If its a glass tube type, they are easily compromised in shipment and installation as to breakage. The old melting metal plug sort will not break in a pressure surge.

    Also, you need a 75 PSI pressure relief valve at the pressure tank, which will be back up to any pressure surges. An adjustable one set to 60 psi would be better.

    Pex supply has a nice double disc check valve, or look at "surplus center' for a SS 1.25" spring loaded ball type check valve. Great quality, and instant closing. I use one on a tank about 200' high, and its 15 years old with no hammer on closing.

    I asume your 'down' pipe is ONLY that, -you are filling the tank from another pipe [?] Get a WIKA pressure gauge, US made, Graingers has a million of choices. Do not buy pressure gauges at the big box. But the gauge is fairly irrelevant - your pressure is a constant due to the laws of gravity.

    Dont call plumbers for water supply issues. Call them for sewage leaks.

    http://www.grainger.com/Grainger/APOLLO-Spring-Check-Valve-1CKT9?Pid=search

    http://www.sprinkler.com/wilkins-700-series-dual-check-valve-assembly

    You can get the Wilkins at Pex Supply for 25 bucks, but its hard to find in their system.
    Last edited: Mar 15, 2011
  7. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    Lligetfa... Your right my water and air gauges were off by 5 psi.
    ballvalve... No I don't wash my elephant with a fire hose.

    Yes my sprinklers have the little red glass tubes in them.
    Yep the lines to the shop and house are down only. The cistern is spring fed with a PV pump on a different valley.

    I called my local Grainger and got 4 of the check valves and 2 presser relief valves. I know a good spot about half way down the pipe I can mount the check valves.

    Would you still install hammer arrestors with the check valves and the relief valves?

    Thank you for the info.
  8. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Dont put 4 check valves in one spot. I assume the pressure tank is at the bottom of the run, you need one just before that, and you could add one or two more on the way uphill, spaced apart more or less evenly. I would put the relief valve at the tank manifold, though I doubt it will ever open with good checkvalves.

    I am not big on the little hammer arrestors, I think their lifespan is not very long and most in houses stopped working long ago. They are microscopic pressure tanks, and we know how often the big ones fail.

    Your water heater may cause the pressure to rise in the house, but the pressure tank and relief valves should keep that under control.
  9. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    Ja, I would expect the little ones with floating diaphragm/separator to eventually fail and the ones without to eventually waterlog if not located with care and the system not drained from time to time. I installed the largest available in such a way that any air bubbles in the stream would naturally get trapped by them. They have not waterlogged on me yet and work as well now as the day they were put in. I think that having entrained air for the iron filter may help to keep them well aired up.
  10. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    I'm going to put one right before the presser tank and one about half way up the pipe to the cistern. I will need 2 for the shop water line and 2 for the house water line when I start the plumbing in a few days.
  11. valveman

    valveman Moderator Staff Member

    Messages:
    4,472
    Location:
    Lubbock, Texas
    I don’t think check valves are going to help. Probably won’t hurt anything, but they are facing the wrong way to stop the hammer. I think Llgetfa hit the nail on the head. You problem was 48 PSI air in the tank with a 51 PSI static. Using a tank for a hammer arrestor the air charge should always be below the lowest pressure possible. When you were using water the pressure dropped lower than the tank air charge. The bladder in the tank was basically stuck to the bottom. So when the shower and toilet shut off at the same time, the freight train of water coming down the hill, hit the system with a closed off bladder tank, and boom it caused a 500 PSI shock wave.

    I would let the air charge down to about 30 PSI. Then your tank will still be able to cushion the pressure all the way down to 31 PSI.
  12. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    Actually, I was thinking the air precharge was higher than the static water pressure essentially having no water in the tank and the pressure concentrated on the small area at the outlet.
  13. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Still, shutting off a shower should not give a surge, and absolutely not a toilet. And if he has the tank at 30 psi and he shuts off his fire hose, he'll probably break the bladder.

    I would keep the pressure relief valve for backup, and the check valves will not allow the pressure wave to circulate its way from 500 to 400 to 300 to zero.

    Those glass ampule sprinkler heads are cheap and I think we will hear a lot more about water damage as its now required. The real ones with the metal plug never wrecked a house.
  14. valveman

    valveman Moderator Staff Member

    Messages:
    4,472
    Location:
    Lubbock, Texas
    I am afraid the check valves may give it a place to bounce back from. Although if it bounces even once, we haven’t solved the problem. Water traveling downhill does some funny things. When you open water at the bottom of the hill, it is like pulling the slack out of a chain. Water can be stretched or comes apart fairly easily, so the water really doesn’t start coming from the reservoir at the top of the hill until you get all the slack pulled out of the chain. This lowers the pressure at the bottom of the hill before water starts flowing from the top. When the pressure dropped below 48 PSI, the bladder closed off the inlet to the tank. So the tank became a cap on the end of the line.

    Then when you shut off a valve at the bottom of the hill, the slack gets pushed back into the chain. Water is not compressible so this only takes a fraction of a second. When there is no more room to push slack into the chain, the long column of water acts like a freight train coming down hill. The closed valve and capped off bladder tank is like dropping a boulder in from of a train. It causes a crash and sends shock waves back up the hill.

    Having a bladder tank at the bottom of the hill acts like crashing the train into a balloon. The balloon absorbs the crash, and there are no shock waves. If there is too much air in the bladder tank, and the bladder is stuck to the bottom of the tank, there is no balloon to crash into. The shock wave bounces back up the hill. If there are check valves in the line up the hill, the shock wave bounces off the first check valve and the process is repeated several times very quickly.

    The bladder tank only has to absorb a cup or two of water to keep this from happening. So closing off a fire hose won’t cause the bladder tank to overfill and bust the bladder.

    A pressure relief valve won’t pop open until it sees the shock valve. This is too late to prevent water hammer, so the bladder tank has to work as a dampener. With dampener tanks I usually pre-charge the tank to about half the static pressure.
  15. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    I can see where some people may think the bladder tank would just absorb the surplus pressure just as it does when a well system comes up to operating pressure. The physics get a bit more complicated. There was a recent thread started by billfig where he was getting unusual results when precharging a new bladder. While I joked that he had a poltergeist, it was a case of his air pressure gauge reading different than his water pressure gauge, resulting in over-inflating of the bladder.

    Some of this may be conjecture because we don't know for sure what design the bladder tank is.

    Some bladders, and the one we are basing our hypothesis on, connect to the tank at only one end and inflate like a balloon. When over-inflated, they press against the small inlet hole and that small surface is all that the water has to push against. Since we are talking about pounds per square inch and there is ony about one square inch, the water pressure cannot deflect the bladder far enough inward to increase the number of square inches it is applying force against. Think of as trying to inflate a balloon. It takes a lot to get it started and gets easier the larger the balloon gets. This is a simplified analogy, so please, no flaming from engineers.

    When it comes to shock waves, time is an important factor. The faster the wave can be absorbed, the less the reflection. When I was working on hardening high voltage transmission towers, it was all about how quickly we could absorb the lightning energy to ground.

    Other bladder tanks, like the WellMate, expose a larger surface to the water at all times, even if over-inflated.
  16. valveman

    valveman Moderator Staff Member

    Messages:
    4,472
    Location:
    Lubbock, Texas
    Good explanation but I gotta disagree with you about the Wellmate tank. Bag tanks, like the Wellmate, as well as diaphragm tanks by others, are usually all called bladder tanks. The general term should be captive air tanks. Anyway, all captive air tanks will seal off the water inlet hole when over-inflated. So much so that there is always a screen or grill covering the opening to keep the bag or diaphragm from pouching out the hole. But you are exactly right about the balloon being easier after it is inflated somewhat. That is why I recommended letting the air out to 30 PSI. That way at 45-50 PSI, the balloon is ¾ full and will easily expand a bit more.
  17. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    I'm learning a lot and thank you. The precharge in my tank was over inflated. I do have it down to 30 psi now, have one check valve at the tank (plan on digging up the hill and putting in one more at some point) and have a presser release valve set at 65 psi.

    I have found a few web sites that have sprinklers with a strip of metal in stead of the glass tube. Are they any better?
  18. LLigetfa

    LLigetfa DIYer, not in the trades

    Messages:
    4,002
    Location:
    NW Ontario, Canada
    The glass tube relies on the weakness of glass to work. The fluid in the tube boils causing a rise in pressure inside the glass tube which ruptures.

    The fusible link is strong below the melting point of the metal.
  19. extendedpath

    extendedpath New Member

    Messages:
    11
    Location:
    S.W VA
    Tank you. I'll be ordering a bunch of heads with the fuse able link for the shop and will see if they will install them in my house.

    I don't know who said it but I'm sure there will be a lot more insurance issues when a bunch of houses get built with sprinkler systems. I know of a lot of places that have large water presser issues.
  20. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    "tank you" - good pun.

    If you are going to sprinkler the entire house and shop, your 50 psi gravity will not cut it, and probably will not make code if anyone bothers to check.

    So here is the sure fire way to satisfy the code and stop the weird hydraulics of water on a downhill run:

    Install a booster pump at the bottom of the hill. Put a check valve just before it. Do a 55 to 70 or 50 to 70+ pressure switch and feed the bladder tank, or use a CSV into that bladder tank set for pressure in the normal way.

    You can downsize the pump a bit because of the high feed pressure. And with a good plumber, you can have him install a nice 3 way valve , so that when the pump and power is out you can switch back to gravity in an emergency.

    Now, the check valves are 'facing the right way' and you lost any possible surges, and you can flood the house when the fire hits.

    I do this with a uphill tank, but the infeed is only 20 psi. And actually, the water flows even when the pump is out, slowly, through the pump, anyway.

    http://www.grainger.com/Grainger/APOLLO-Ball-Valve-1CKG5?Pid=search

    http://www.teksupply.com/farm/suppl...&division=TekSupply&pageId=ItemDetail&isDoc=N

    And here is the sabotage of America, the pump you DO NOT want:

    http://www.grainger.com/Grainger/DAYTON-Multistage-Booster-5NXZ5?Pid=search

    Graingers closed out all their booster pumps that were US made - and they were the SAME price [mostly less!] as the Chinese pump. GREED. And the nail in the coffin of our industry.

    http://www.grainger.com/Grainger/DAYTON-Booster-Pump-2P280?Pid=search
    There is the USA pump, on close out, less than the Chinese. Amazing. Give them factory jobs and give us Mcdonalds. Great plan.

    I just bought a 3 phase 2 HP booster pump, 12 stage for $194. Marked down from $900. [thank you [tank you?] for making me search for pumps] If you do this, you will need careful sizing for the pump. The link I gave you for TEK shows a 16 stage pump - too many for your app.
    Last edited: Mar 18, 2011
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