Water tank construction

[krusty]

Any helpful hints and/or success stories regarding water tank construction? I am building one for our new RMR and am concerned about "swelling" when the pressure in the system rises, as any bulges may interfere with the proper operation of other components. I'm planning on allowing up to 20 psi before relief. I had planned to use .125" 3003 H14 sheet. What I'm seeking is construction methods that allow the tank to keep its shape under pressure. The tank, to fit the available space, will be rectangular (length 30", width approx. 12", height 16").  Running out of time!    TIA, vic

[Seldom Seen Slim]

Well, I can point you towards a few discussions -- but I don't have the exact links.  Look for Johnny Hotnuts' build on his car -- I think I remember quite a bit about his water tank build.  Also Dr. Goggles has recently talked about it.  Did you try searching for water tanks using the search function? 

There -- three ideas for you to research.  Good luck.

[Dr Goggles]

 If you build the tank with multiple baffles it will be very well braced. Your base is 30X12 and you have 16 inches in height , if you had 6 or 7 pieces of 28X12 cut you would weld them as "floors" every two inches or so with the gap alternating from end to end . That way the water has to take the longest route , avoids convecting and there are few dead spots. You can also put vertical baffles on each floor forcing the water to take an even longer route before dropping to the next level . I say dropping because it will work better if you put the hot in the top and take the cold from the bottom.

Making our water tank was one of the noisiest weeks during a very noisy time in my shed. I fully expected at any moments that one of my neighbours was going to jump over my fence and beat me to death with a hammer, and they are all decent , reasonable people.Making a 16 Gallon box out of heavy steel plate with the associated cutting , grinding and general bashing leaves the mowers, weed-whackers and usual suburban noises for dead.

[krusty]

@ SSS - thanks for having me slog through all those Hotnuts posts!  JH used a small 5 gal or so former air tank - not too applicable for me. And yes, I did try a search (although I am not the best of searchers). See you Friday @ Maxton? (I'm coming down for a pre-tech).      @ Dr. Goggles - thanks for the recapitulation of the "maze" method - it's what we were planning on. I'm more interested in proven designs that help prevent swelling or bulging under pressure. I sure hope I don't have to resort to boiler plate! What gauge metal did you use? Have you experienced any bulging and resultant distortion under pressure? Thanks for your help.    vic

[interested bystander]

Methinks .90 is more thickness than you need . Less thickness easier to handle, especially if you gas weld the seams.

Built an H2o tank years ago that filled the ENTIRE rear deck -trunk of a '29 Landspeed   roadster out of .090. 3003.
Had a 6''grid egg-crate baffle assembly that floated in side. (Built 3 sides, then installed it and welded the last side).

[akk]

I have used a ten gallon portable air in two of my cars. Costs about 30$ at the auto supply. We set up the return to tank (two # 10 hoses .. one from each head) to restrict water flow so that at about 5000 rpm the block is pressured to about 20 psi. The tank is vented to atmosphere. The pressure in the block prevents boiling in the heads and associated hot spots. We only fill the tank half full after the block is full. On a good run the water heats up to about 185 F. ( the boiling point of water at Bonneville altitude) and stays there thru the 3-4-5 mile marks. We boil about 1 gallon off max. on a run. The reason for half filling the tank is to make room for the water to puke out of the motor at the end of the run (when the motor slows down the block pressure drops and the water boils in the heads). The tank has no baffels, the return lines return at the top of the tank tangential to the tank wall to let the water swirl, depressure and flash steam to dissipate heat. Mount the tank high enough so that the water level is above the water pump(or the pump will not prime). Vent the tank with a hose to a place no one will be standing around the car. If the tank is too full when the engine is shut down severe burns can result!

[1212FBGS]

the internal baffles are a must especially so you can stop the slosh of water going forward when the parachute hits... you can also cut holes with a hole saw in the top and bottom and weld in tubing for strength/stiffness, this will also aid dramatical in exterior surface area for heat dissipation...
Kent

[McRat]

I'm working on a water tank right now as well. 

Should I make provisions for pressurizing it beforehand?  In other word put a schrader valve on it, then take it up 15psi static?  This should reduce the size of any air bubbles trapped in the heads/block by 50%.

[akk]

You do not want the tank to pressure up! The drop in pressure when the water returns to the tank lets the water boil in the tank and release heat. If you pressure the tank, water temp will build untill the vapor pressure exceeds your relief valve ( at 20 psi this is about 240 degrees), then the water will start to boil every where including in the heads. Pressure the block not the tank. If you want to use a relief valve put it in the return line. We use the restriction of the return lines because it is simple and reliable... we also fear that relief valves in the return lines can result in unequal flow in the heads.

[McRat]

Interesting.

Anyone have a number for how many gallons a minute a normal (mechanical) BBC water pump flows at 5000 rpm?

[Ron Gibson]

Anyone have any info on how much pressure a BBC mechanical water pump makes in the block and heads at RPM? Years ago I heard (maybe old wives tale) that a 855ci Cummins  ran 40 lbs in the block. The more pressure in the block and heads, the fewer hot spots due to boiling.
If you have enough water tank capacity to cool the engine for the entire run, could the whole system be pressurized as McRat asked? I understand the venting of steam but if there is enough water to absorb the heat of the steam, would venting be necessary?
Not questioning to contradict anyone's opinions, just learn.

Ron

[Jonny Hotnuts]

I'm working on a water tank right now as well.  

Should I make provisions for pressurizing it beforehand?  In other word put a schrader valve on it, then take it up 15psi static?  This should reduce the size of any air bubbles trapped in the heads/block by 50%.

No, the system will self pressurize once the system runs for a few minutes it will be at 15 psi anyway. You will need to get the air out before the system is run, trying to reduce the size of the bubbles by pre pressurizing the system is attempting to put a band-aid on a broken leg.
Some say to pre pressurize the system, well if  you do this you will need to pressurize it with pressurized water because pressurized air will introduce more air into the system.

There are a lot of misconceptions about cooling.....
One is that pressure is built by the water pump and the pressure is developed agents a flow restriction. This is BS, the pressure is made when the water is heated. Last year I ran no thermostat, no rad with electric pumps (make 5 psi head) and still was able to make 17 psi coolant pressure at the end of a run. Pressure in a coolant system will continue to build until the thing explodes unless it has a pressure release system (radiator cap for instance) if continued to operate beyond the limits of its cooling ability.


Remember.....

-You do NOT want the water to boil, this will develop hot spots (same as air bubbles).
-In a sealed system the pressure will be equal in all parts of the system, thermostat be dam*ed....meaning if its boiling in the tank its boiling in the head....boiling water in the head means you will have hot spots and detonation.
-You need to have adequate water volume OR cooling capacity to prevent boiling.
-waters boiling temp is decreased 3 degrees per pound pressure in the system. This means at 15 psi you water will boil at 45 degrees hotter than if not pressurized.

Good luck.

~JH

[Dynoroom]

I'm working on a water tank right now as well.  

Should I make provisions for pressurizing it beforehand?  In other word put a schrader valve on it, then take it up 15psi static?  This should reduce the size of any air bubbles trapped in the heads/block by 50%.

There are a lot of misconceptions about cooling.....
One is that pressure is built by the water pump and the pressure is developed agents a flow restriction. This is BS, the pressure is made when the water is heated. Last year I ran no thermostat, no rad with electric pumps (make 5 psi head) and still was able to make 17 psi coolant pressure at the end of a run. Pressure in a coolant system will continue to build until the thing explodes unless it has a pressure release system (radiator cap for instance) if continued to operate beyond the limits of its cooling ability.

~JH

Johnny, if what you said is true why does my block water pressure go to 35 psi on my small block as soon as I start it on the dyno and pull some power? Waters not even 100 degrees yet.


McRat and Ron. Most big block pumps (depends on who's it is) will make about 35-40 psi block water pressure. Do not spin it faster than 4500 rpm as it can/will cavitate above this depending on the construction. This is true if you run a restrictor or a thermostat. The cooling system pressure is a different issue and normally will hold around 15-25 psi depending on the system type.

[JimL]

I'm not sure how you can build pressure in the cooling system without air, or some other compressible gas.  Water won't compress...you can put pressure on it, but you're doing it with gas propogation or mechanical means (and mechanical means does NOT reduce the volume of the water).

Generally, when I see pressure come up in the cooling system, shortly after start up and when load is applied, that is a sure sign that the head bolts/studs are inelastic.  The heads will start to grow quickly, and the gas leakage past the fire ring stops quickly....but cooling system pressure takes a jump when read directly.  Usually, I see the head bolts/studs overtorqued.  This can be really ugly when running aluminum heads.

Back to the original question about the water tank....a little personal experience (more like personal screw-up, but HEY...we're all friends here);  we built the cooling tank for the 797 Roadster out of some heavy stuff, with big strong baffles, and a 14 psi cap.

When the headgasket blew (after boost pressure got so high that the combustion chambers moved up and bent the head) the pressure in the tank resulted in "form fitting" it into the car.  The problem is that a 14 psi cap can't flow as much out-gassing as a broken 2-liter turbo engine can make!! 

Bobby Sights had to unravel that mess (sorry Bob) and if I had it to do over, I'd have fitted a real blow off valve (away from the driver area), in addition to the pressure cap.  That way I could have chosen where the steam went, instead of into the cockpit.... and watching my driver turn in to the center of the course in '99 with what appeared to be smoke pouring out of the cockpit.

I'm real glad there was an extra panel of sheet metal between the tank area and the driver....but I sure could have done better, hindsight being 20-20.  Anyway....leave some room in case you swell the tank...you may need to take it out without cutting tools!

And plan for the day that something blows and a hose or connection has to burst....you can decide where that should occur, in the system and away from the driver.

Regards, JimL

[Dr Goggles]

I'm not sure how you can build pressure in the cooling system without air, or some other compressible gas. 

good table here....

http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html


and then this from Jack Dolan.......

The last water tank that Nolan built was measured to fit the frame in the nose just as tight as could be made.
IT was a beautiful job of fitted and welded aluminum.
It was all straight cut pieces with some folded corners and the rest was welded and fit pretty good.
That evening ,I came over to check on the progress and found the tank was all radius in the panels and really fit the space available.
 I had no idea who and how all that extra work happened , but now it was better than ever.
As we were locking up that night he said "I saw you looking at the tank and you never actually asked about it." What happened, was during the day he fired it up and chuffed a head gasket into the water jacket and the squeeze from 1 jug " PILLOW POOFED" the tank to fit.
It was an unintentional result ,but he silently enjoyed the credit for all the extra work.
 If you were brave enough to ask , he was brave enough to share the truth.
That is really the important part for both sides that needs more work.