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Old 12-04-2011, 08:51 AM   #1
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roof top tank, Taiwan


Lets start by saying that i live in Taiwan, and things are a bit different here. The public water works gets the water to your house, but you are resonsible for having water pressure in your house, Although the 1st floors usually have great pressure, as you go up floors the pressure decreases, not to even mention the peek times.

So to solve this issue everyone has a pump and rooftop tank or two. or three.

I my house, which i rent, there is a pump and a tank. however, i have come to beleive that the people who installed it didin't run the pipes correctly.


This is the way it seems. I say seems as most of the pipes are in the concrete walls.



I have come to believe this is the way, because of two reasons. If i leave the pump running the tank will overflow, even with the bobbing valve functioning, as it it obviously just filling from the out of the tank, and if i turn off the pump when the city pressure is low, my tank emptys.

So what i am asking is for you to confirm my belief before i goto the lanlord with demands, of hire an expert outside her knowledge.

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Old 12-04-2011, 09:41 AM   #2
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roof top tank, Taiwan


I believe you are correct in your second drawing----

As it is-- your system is adding pressure to the cities water system---when the city pressure drops--the tank will drain out.

A separate problem is the overflowing---your pump needs to know when the tank is full--a float switch is needed to turn off the pump when the tank is full---That 'bobble switch' --is it a float valve like the guts to a toilet? or is it an electrical switch to turn on and off the pump?

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Old 12-04-2011, 10:14 AM   #3
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Oh Mike,
would a check valve on his side of the city pump cure anything? Looks like it would at least stop his storage tank from draining when the city pressure is low. Not sure how big the tank is but obviously they have the tank there for reserve during peak times. At the very least it looks like it would prevent his pump from putting pressure back in the city line.

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Old 12-04-2011, 10:25 AM   #4
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You are right a check valve (back flow prevented) might just do the trick--As a matter of fact--I bet that there is one already in the system and it has failed----without one the original system never would have worked properly---

Good call---
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Old 12-04-2011, 11:19 AM   #5
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roof top tank, Taiwan


this one way valve might stop the loss of water but wont stop the over flow, but i guess if i pt a simple bobbing level check to shut off the put, or to turn it on rather when the level is ow, that woud solve this problem.

All his is great, but I also have an issue of the tank not creating enough pressure to turn on the in line gas heater. I have to run the pump to have hot water. I figured it was because with the tank opeon, and the pump off, it was easier for the water to flow else where, but with a closed system, it shuld have enough gravity force . the tank bottom is almost level with the heater, just sligtly above.
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Old 12-04-2011, 11:32 AM   #6
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roof top tank, Taiwan


Sounds like the low water level in the tank is causing the water heater to shut off because it is not filled--

Cure the tank and pressure problem and the heater problem might take care of itself---

I like the closed system (with the separate water feed line) but the cost to do that in an existing structure might not be practical.

Yours could be made to work---with a working back flow and better shut off to prevent over filling the tank---
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Old 12-04-2011, 12:17 PM   #7
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roof top tank, Taiwan


I don't think it matters whether the left or right diagram is true. Either way when your are don using water the needed float activated shutoff will stop the pump when the water reaches the top of the tank.

An alternate system that also works with either the left or right diagram has a sealed tank with some air and some water in it. The pump is turned on and off by pressure, not water level. As more water is pumped into the tank the air pocket is compressed which causes the pressure to rise. At a certain pressure the pump shuts off. When you use water, the air pocket in the tank expands, the overall pressures goes down a little, and the pump starts up again.

The air is needed to allow the pump to maintain a reasonable pressure and also refill the tank at its leisure as you use water. There must be a reasonable amount of water in the tank after the pump shuts off so you can use a reasonable amount of water even if the pump is not able to keep up until you are done using water.
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Last edited by AllanJ; 12-04-2011 at 12:22 PM.
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Old 12-04-2011, 12:46 PM   #8
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I'm certainly not an expert (or even a plumber), i'm just a flunky trying to help, so i have a couple of questions.

The tank-is it a sealed tank (that will hold pressure) or is just a storage tank with a lid, that gravity feeds your pump?

what type of water heater is it? Tankless? conventional?

When you say things are different in Taiwan, i think we maybe are taking some things for granted that may not be so with your particular situation.
A few more details might make us look at it differently than we are used to here in the U.S.

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