Diy pressure / expansion " tank"

animatt

 I am building and off grid house in mexico. I have had a thought for a while about a diy expansion tank. Of sorts that is not a traditional tank. Container or reservoir maybe better term.

Anyway,

I would prefer not to take up limited floor space with a tank. I was thiking of taking some 6 inch pvc I had.

Basically on the pressure side of my water system tee off.  This tee would be close to the ground immediately following the tee would be an isolation valve as well as a drain.  All this upto this point would be small diameter stuff 1 inch max.  From here piping would go vertical up 8 feet in 1 inch pipe.  And adapt to 6 inch pvc.  The 6 inch pvc would be buried in the cieling always with a gentle slope and poured in concrete.. Finally at the end just capping the pipe.

With this pipe I should be able to get close to 60 gallons of volume in the pipe.  The idea is the piping can have air in it.
It would not have a bladder but should act as somewhat of an expansion tank.  

After  while air would be disolved in the water at which point I would spin the isolation valve and drain water and charge with air again.  To me seems like this system with a little maintenance should last for a long time.  The 6 inch pvc would be poured in cement.


I am not sure if I am overlooking something.  I would not want to have to drain the 60 gallon reservoir every week.  But once every 3 months maybe acceptable.  Obviously longer periods would be better.  But not having to replace pressure would be nice.

Any thoughts would be welcomed

westbranch

I used a 3 foot x 3 inch PVC in my camper for the same application to slow down the cycling of my little 12 v pump.  I installed a bicycle tube type air valve in the side near the capped (glued) end... turned on the pump , pressurized it and the put in some air till it could be heard going down the pipe while a tap was on a trickle...  works fine 10 years on... also use the air filler to blow out the lines each fall.. anti freeze goes only into the pump which is at the bottom...

zoneblue

The locals here use something similar. 4 inch pvc standing vertically, water comes in the bottom, air valve in the top. Without a bladder you have to charge them more often, but this is how pressure tanks worked before the modern bladder ones came along.

animatt

Excellent good to hear.
I was hoping it would work as now I can hide pretty much the whole setup. I do not mind having to charge it every so often.  Any idea how often recharging is needed. Are we talking once a month.

BB.

Here is a nice blog post on air over water pressure tanks:

http://terrylove.com/forums/index.php?threads/pressure-tank-maintenance.20849/

Get an Air Volume Control and some check valves to automatically inject a bit of air into the tank when the well pump cycles--and it sounds like a pretty automatic system.

-Bill

m151

You could adapt an air volume valve from another tank. They are somewhat universal and should cost under $20. They are in stock at many Sears stores. However, most people that have switched to a bladder tank will never go back. It was a great invention!

zoneblue

Agreed. Except the bladders dont always last terribly long. Especially if you forget to charge them. Without a bladder, charging them every few weeks will be required. With bladder, you have to check them every other month at least. Either way it requires depressuring the water line.

Aguarancher

I would say you guys may be way over thinking this. I have a 125gal. vertical galv. tank that has been in service for over 30yrs. On the top of the tank is a “T” with 2 ball valves. One is open to air as a ‘vacuum breaker’ for draining down the tank; the other has a Schrader valve for charging the tank. Never trust a Schrader valve by itself.

 On the very bottom of the tank is a drain valve for setting the water level and flushing out any accumulated sand. About a foot off the bottom of the tank is where the pump and house both connect, like with a bladder tank.

About 3-4 times a yr. I have to reset the tank as the air saturates into the water. I just set the water level in the tank about 2/3 full by the ‘touch your hand to it’ method, and pressurize the tank to my cut-off pressure. 5min. job and we’re off to the races.

BTW if you are having to re-charge the bladder in a bladder tank anymore than every 6mo.. you have a bad Schrader valve or bladder.

Dave Angelini

Aguarancher said:

I would say you guys may be way over thinking this..

BTW if you are having to re-charge the bladder in a bladder tank anymore than every 6mo.. you have a bad Schrader valve or bladder.

Dave Angelini

The bladder pressure check should go for years, mine is 19 years old and I never do anything but put rainwater in it.
One thing to do is to listen to the sound the bladder makes when pressurizing. When that changes, you have a problem.

Solar2

I realize this is an old post but here goes.

The volume of an 8 ft piece of 6" PVC is more like 12 gal.
The "draw down" is a small fraction of that.
Draw down is the amount of water you get for a pump cycle
which depends on your low/high pressure switch settings.
Best utilization of a pressure tank comes when it is pre-presureized with air to the low switch setting.
This is true of both air tanks and captive air tanks.

Back in the days of surface mounted suction pumps it was not uncommon to have to bleed air from the tank,
or put up with air rumbling through your piping and spitting out your faucets.
An upside down steam trap worked good for an air bleed.

There used to be tanks available with floats in them.
The float was just slightly smaller that the inside dia. of the tank.
The tank was mounted vertically such that the float would sit at the water surface.
This greatly reduced the amount of air adjustment needed.

jonr

I've seen a lot of people build towers and put water tanks on them.   Mostly because utility power and/or water can go out for long periods.  They seem to have no interest in batteries (too complex).  It would be interesting if there were a way  to create large (say 200+ gallon draw-down) pressure tanks for less cost than a small steel tower with a plastic tank on top.    Encase a plastic tank (with inner-tube bladders) in concrete?

Dave Angelini

About 1/2 of the houses in  central america has a tank on it's top floor.

jonr

A disadvantage is that a pressure tank needs to be about 3x larger.   On the other hand, a tank with little elevation doesn't produce much pressure (usually < 10 psi).  And a pressure tank can be hidden vs the rather ugly elevated tank.  And it can be protected from freezing.

A 4'x4' panel with 60 psi behind it produces 138,000 pounds of force.  Perhaps hard to contain with concrete.

mike95490

Look at old RR water tanks:

Dave Angelini

nice tank!  Where Mike?

jonr

Looking at the numbers, for anyone that already has batteries, pressurizing household water at the time of use (ie, no elevated tank or a minimal pressure tank) is the most practical (it's just not enough watt hours/day to worry about).

BB.

12 or 24 VDC RV pumps are pretty cost effective... They can last 2-7 years or so and do no use much power. Better for smaller home/installation. No pressure tank, or "small" surge tank.

An "off grid friendly" well pump with larger pressure tank is nice--But not cheap (pump with VFD internal controller especially).

A "not off grid friendly well pump" (jet pump, standard induction motor well pump) has very high surge/running current (pump may be "cheap", inverter+battery bank expensive; or pump to cistern with genset--Cheap but several times a week to start/maintain genset).

For in-well pumps/induction motor based--Those with an "external well head capacitor" tend to have lower starting current vs those with capacitor "in pump" (or other starting methods).

Any "special" water needs? Tankless water heaters have minimum flow/pressure requirements. Pump needs to be sized to flow shower/tub/sink hot water. Smaller tankless will run 1 point of use at a time. If two or more points of use (shower+irrigation) needs to designed for (possibly two pumps--one for in-house, second for irrigation).

-Bill