Happy Birthday to me

It's 5:13pm, and I'm sitting in the shade in my back yard, tweaking some really neat flexure mounts, while keeping an eye on two of my kids and two of their friends frolicking in the pool I built years ago. It's hot out, and there is steady traffic between the two hives near the back of the yard and the fountain to my right. A pair of ducks have been watching the kids too, and though they like the look of all that water they're leaving for someplace less noisy.  Lady Jane, our black Labrador, is lying in the grass, which is overdue for mowing, ripping up stems and chewing away. There are stains from fine droplets of sunscreen on the back of my laptop that won't be coming off. Martha will bring my youngest daughter back from gym class in an hour and then we'll head out for my birthday dinner.

At least once a day, at least one person helps me accomplish something I cannot achieve myself, things I am really happy to be working on.  I wonder if I manage to help someone else every day in the same way.

I have a lot to be thankful for.

Lanthanum Phosphate

As you know, I've built this nice new pool. The pool is designed to stay at 85 F for most of the year, and so it has solar panels in their own insulated glass boxes so that it can collect heat even when the outside air temperature is low. Because those panels can get ridiculously hot (338 F) in the sun when water is not flowing through them, they are made of copper rather than plastic as is more commonly done. I've been learning the consequences of that difference.

A couple weeks after filling the pool I added chlorine (hypochlorous acid, HClO), which immediately caused a brown stain on my nice white plaster pool. Copper from the panels had leached into the pool water in the form of copper ions. The HClO oxidized those ions, probably to Cu2O, which promptly came out of solution and bound to the plaster. So, now I have a brown pool. It really pissed me off for a while, but I've grown used to the look and now I actually think it looks good in some places. One of the interesting side effects of having all this copper in the water is that the copper is antimicrobial. The pool has often gone for days with zero chlorine, at 92 F, and with tons of phosphate, and has essentially no algae growth. Without copper that would be a recipe for an algae bloom.

I have these little strips that claim to test the copper content of the water, and that test result drops to zero shortly after I add chlorine. After four or five days it will bounce back up to 0.5 ppm (ppm meaning mg/liter in this case). That means my 38500 gallon pool has 2.5 ounces of copper in it that used to be on the roof. Clearly I can't go on like this for too long, or I'm going to have pinhole leaks in the roof panels. Happily, I've noticed recently that the copper seems to be zero even after a few days of no chlorine, and if this is real, it means the copper has stopped leaching into the water, perhaps because I now have a protective patina on the interior of the pipes.

In my various attempts to keep my white plaster white, I added "chelating agents" to the pool. These things are basically dish soap, and load the water with lots of phosphate (HPO4 2-). The idea is that the phosphate ion will preferentially bind to the copper ions and form Cu3(PO4)2, which is insoluble in water. Presumably this copper phosphate doesn't bind to the plaster but instead can be filtered out. In combination with a low pH this was supposed to reduce the Cu2O in the plaster, then convert it to Cu3(PO4)2, but if that was happening it sure wasn't obvious. I eventually gave up. This exercise left the pool with over 2500 ppb phosphate, which is way too high. When the copper levels recently stopped going up without chlorine, an interesting thing happened: algae! So this weekend I determined that it was time to take out that phosphate.

One takes out phosphate by adding Lanthanum Chloride. This reacts with the phosphate to make LaPO4, which immediately comes out of solution and forms this white fluffy stuff on the bottom of the pool. I tried vacuuming this up -- big mistake. The stuff will plug any filter, instantly. I tried a few times adding lots of DE to the filter, and gave up. That's when I read online that you have to vacuum this stuff out of your pool entirely, just dumping the water to the street. Then I realized I hadn't really plumbed my pool with an option to vacuum to waste. D'oh!

[Update: fixed the plumbing so I can now pump to the street or sewer. Since I have very low-resistance pipes, it looks like I can pump over 80 gallons/minute to the street, which is very impressive to see.]

For a little while I was feeling pretty beaten. The phosphate levels weren't reading any lower, the pool was a mess, I had no plan to get it clean, and my fingernails were gone from cleaning the DE out of the backwash tank. This Lanthanum Phosphate is amazing -- a tiny amount turns DE into a watertight membrane, something like Bentonite clay.

Then I got back to work. I pumped the water out of the spa, then set the valves to bypass both the filter and backwash tank, suck from the pool and return to the spa. With my vacuum in place I was vacuuming the pool into the spa. Before turning on the pump I put a sump pump in the spa and pumped it out into a hose which went to the sewer. Yes, this was pumping phosphates into the city's sewer. I think I pumped out about 2.5 pounds of phosphate, or about one box of dishwashing detergent. I had no copper in the water, nor any chlorine, and my pH was 7.5. It shouldn't be a problem for anything downstream. The vacuum sucked everything off the bottom and we dumped about 800 gallons of water, or $2.40. Even better, my phosphate is now down to 300 ppb, which isn't perfect but it's nice to be out of the unmeasurable range.

In doing the research for this blog post I found out that my tap water already has around 190 ppb phosphate in it, added by Los Altos to control corrosion in copper pipes. So, I need to measure my copper levels now that I have low phosphate to see if I'm back into corroding my solar panels. Hopefully something else is protecting the panels.

Also, I've learned that the patina that can protect copper is soluble in ammonium salts. That's significant because ammonia in the pool is what you measure when you measure "combined chlorine" (really chloramines). It seems I'm going to have to stay on top of that, not just because chloramines are smelly eye irritants, but because the stuff attacks my panels.

I can keep after it with adding chlorine, but my main line of defense was supposed to be a nightly dose of ozone, intended to burn anything organic down to N2, CO2, and water. The ozone is on hold until I can re-cover my DE filter grids in stainless steel mesh, instead of the polypropylene mesh they have now. Meh. More work. Some other weekend.

[Update: stainless steel mesh won't hold diatomaceous earth. I got some mesh samples and tried pouring DE mud on them, and it fell right through. Under the microscope, it's clear that DE grains are just tens of microns across, and so a macroscoping mesh isn't going to do it.

I've read that glass is compatible with ozone, so I'm going to try fiberglass as a filter material to hold the DE, and we'll see how that goes.]

[Update2: BGF fiberglass filter fabric style 421 style 580 holds diatomaceous earth just fine. I had to hand sew it with stainless steel wire, since fiberglass strands are completely useless for sewing, as they fray and break at the slightest provocation. Next up: long term test of fiberglass grid covering to see if it breaks or does some other bad thing.]

Pool is filled

Thursday was a big day for all of us. Any passers-by seeing the girls running around in bathing suits for a few days now may have guessed the reason: we plastered and then filled the swimming pool.

Quick pool status

Patio around the pool is mostly in. Hopefully today they will finish off the corner around the pump vault.

Saturday I had hoped to install the last of the tile mosaics, but instead I found the remaining big Orca cracked in the center, and the north side dolphins had cracked as well. We cut them all off the wall and will reinstall the lot next weekend.

The tilework around the hot tub was fairly tricky. Here's an example of a three-way miter. The tile guys kept looking at me like I was cuckoo. As I explained, you cut it by cutting each of the three two-way miters. It's actually pretty straightforward if you just do it.

The hot tub as a whole. In the background, you can see the breaching Humpback mosaic, along with a portion of the Orca mosaic. The Orcas are the ones that have been giving me so much trouble.

The Toy I Always Wanted

When I was a kid, I used to dream that I could make stuff pop into existence if I could just imagine all of the details.

Now I have SolidWorks.

I draw stuff. It takes a really long time to draw anything, compared to doing it by hand, just like I imagined it would. But once you get the hang of it, you can push a lot farther than you can with hand drawings.

Once drawn, I crank out dimensioned drawings, and then call people who build things for me. And they look just like the drawing.

This is what I wanted when I was 8.

Last weekend I made a model of one of our new gates.

Then I made a drawing of that:

While I was at work this week, Jesus came by and built it for me, and now I have the first of three new gates:

Obviously, this isn't quite the same as what I drew. The back gates are much shorter than the front gates. Jesus doesn't need a seperate drawing for each gate, just the idea of what I want.

I started out with hand drawings of the gate, and for this project, I probably could have just left it like that. But it turns out that hand drawing curves, and trying out lots of different curves and ratios to see what you like, is not so easy. With a parametric CAD system, you draw it once and then fiddle with a few numbers until you like the way it looks. Much better.

Coping being cut

Our in-ground pool is actually raised out of the ground slightly (18 inches near the house). This makes the side a nice bench to sit on, keeps cut grass from blowing into the pool, and should interfere with running and jumping into the shallow end at a steep angle.

One consequence, though, is that our coping stones are a nonstandard width. We've decided to have bullnosed coping (so these are bullnosed both sides, also nonstandard), and that requires that the coping overlap the waterline tile by over two inches. This kind of thing adds up:

• Waterline overhang: 2.5 inches
• Tile thickness: 0.25 inches
• Thinset: 0.375 inches (that's a lot, to give the mason plenty of freedom to flatten the wall for the enormous glass tile mosaics that are going in)
• Bond beam: 12 inches
• Thinset: 1 inches (the outside of the bond beam is quite uneven)
• Facing stone: 1.25 inches
• Exterior overhang: 2.5 inches

All up, we've gone for coping that is 20 inches wide.

We actually had a order placed for some very nice pearl white travertine (from Olympic Stone). When it came time for them to come by and pick up the check... they didn't. We called back and found there was some sort of problem... they didn't actually have the stone. it would be a 3 month delay to get it from Turkey.

Well, that's never a good thing to tell a customer. Martha started looking around, and found another very nice stone, this one a three color granite, from American Soil. This one is more expensive, but it really is pretty, and it's available right now. We ended up buying it. (We may use OSM's pearl travertine for the face of the pool rather than the coping, since they apparently have the 1" stuff available.)

[Update 16-Nov-2009: The pearl against the walnut travertine ended up not looking as good as we'd hoped, so we ended up using the walnut travertine on the sides of the pool. You can see this in the mid-November post.]

By "it", I mean a 12 ton boulder imported from Columbia, California. You can get a sense of scale from the pickup truck at the back right. This rock is a little shorter than I am.

It came from over here:

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They're chopping this thing up into 20 inch wide by 36 inch long by 2 inch thick coping stones for us.

This is a cable saw. The cable has some kind of abrasive on it (I've never actually seen the thing stopped, it appears to be running all the time). The huge wheels drive the cable through the stone. Above and below, they're whacking the top off the boulder.


Below, they're cutting the ends off. In this pass, the rock stays put and the machine basically drops through it at a half inch per minute (I'm not really sure, as I never saw the saw make any noticeable progress through the rock).

Here's one of the slabs coming off the cable saw, going into their indoor facility for shaping. You can't really see all the color here, but there is white, black, and some pink to it.

Here's the rock all chopped up:

There's a lot of white in some of these. Hopefully they'll be able to cut around that to some extent.

Not so much in others.

This equipment is usually used to make countertops.

American Soil just got a brand new Italian machine for cutting and bullnosing. This isn't it, since apparently that machine can't cut a straight line just yet.

Each stone should weigh about 140 pounds. I'm sure the mason will be very happy to hear that.

I'm really happy with how this looks. We still have some risk, in that the coping could have huge blobs of white in it, or the grain could get mismatched, but the folks at American Soil seem to be on top of that.

We've also picked up all our glass tile. It gets installed after the coping, but I'll try to post some pictures of the pieces assembled in our garage so you can get a feel for it.

Fastest Freestyle Ever

The men's 400 meter freestyle relay at the Beijing olympics was amazing. The French team absolutely crushed the world record time, and the Americans squeaked past them. Right up until the last 50 meters, the French were in front.

Don't talk to me about Michael Phelps, the second-slowest guy on our team. Let's talk about Jason Lezak. Jason gets in the water at 2:38. (Watch the video here.) Look at his stroke compared to France's Bernard Alain. He looks pretty similar (to my untrained eye). And he turns in a time on that first 50m that is pretty similar: 21.50 versus Bernard's 21.27.

And then, after that last flip turn, Jason Lezak swims the next 50 meters in 24.52 seconds. Which sounds slow compared to those first 50 meters, but it's so fast compared to everyone else that he was one of only 3 guys in that race to swim in less than 47 seconds... and he beat the other two guys (both French) by 0.57 and 0.67 seconds. That's HUGE. He nearly did it in less than 46 seconds.

Watching back in August, it was immediately apparent to me that Jason changed his stroke after his flip turn. This morning I looked up the video on the internet, and it raises more questions than it answers.

First, Jason takes 34 strokes to Bernard's 42. It's not like Bernard is some short French dude -- at 6'5", the guy is actually an inch taller than Jason. Discounting the 7 meters that both guys got off their kick at the end, Jason managed to go 49.8 inches on each stroke, vs the paltry 40.3 that Bernard manages. And, since Jason is going faster, he's got more drag and so his hands should be slipping back more. Where did he come up with an extra nine inches?

For those last 34 strokes, Jason's form appears to go to hell. His timing is no longer even -- the delay after throwing his left arm forward is less than the delay after his right. Worse still, the change in timing has his left hand grabbing the air that he's blowing out, which has to be terrible for maximizing the purchase on the water the whole way back. Compare to Bernard, who efficiently vents smaller bursts of air under the left portion of his body while his left arm is airborne.

Notice something else that Jason is doing. He's ducking his head down after he takes a breath. And watch his right shoulder roll. When Jason pulls back with his right hand, he launches a portion of his torso up, over the water, and then when he pulls back with his left hand he is porpoising the right half of his body over that water.

Has Jason incorporated some of the body motion of the butterfly into his freestyle?

Another insulated pool

Back when I posted about the insulated in-ground pool that I'm building, I asked if anyone else is building such a pool. I've received a few answers:

• One reader in Melbourne is building such a pool.
• Several have been built in the United States, but only one of the ones I've heard of is residential. The rest are all commercial facilities.
• Insulated pools are standard when the pool sits on top of a parking structure. Apparently installations like these are simply impossible to heat if the pool is not insulated, and there are structural isolation benefits as well.

Up until now, though, no pictures! Thankfully, the reader from Melbourne has recently written in to share a few pictures of his insulated pool. Here's the standard picture of the dig:

The pool is 46 feet long, which is exactly the same length as mine. His is skinnier (10 feet wide) and more shallow (max 6 feet), which is appropriate for a lap pool. Below, it looks like they are installing an in-floor cleaning system. Very nice.

Below is a pic of the insulation going in. He is using Dow Highload 100, sold there as Dow HD300, in the same thickness that I used (2 inch). He says:

The insulation I'm using is Dow HD300 in 50mm boards. This product is made for insulating under coolroom floors with trucks driving on top, and is overkill given its compressive strength specs of 2% compression (1mm) after 20 years of 250 kPa or around 25 tons per sq meter. However, the pool contractor and engineers had never seen pool insulation done before and through an abundance of caution over-specified for the highest compressive strength product they could find to be sure it wasn't going to settle. With the loads from this pool of only around 2 tons per square meter, we have more than an order of magnitude margin of safety. In the end, the cost differential between this and lesser rated products was so small that in the interests of getting the pool contractor comfortable with signing off we went with the HD300.

The contractors didn't glue the boards to the soil with foam, instead they used the rather unsubtle method of nailing it through with steel rod. I had two concerns about this:

• This will mean there's some heat conduction losses through the steel rod from the soil to the concrete, though the total surface area of steel in contract with the cement shell would still be minimal so this probably isn't a big deal.
• A risk of the rod eventually rusting and applying pressure to the concrete shell, but the foam will (I hope) compress enough to accommodate any rust expansion and prevent concrete spalling off the shell were this ever an issue.

The upside is at least I don't have to worry about the compression issues for the expanded foam glue you'd used and hence avoids the risk you mention in your blog that this may place extra strain on the shell as it settled, and from the photos it seems the contractors have got a good solid base without the rocking problems you'd mentioned.

The steel rod seems like a good idea. I tried to find an equivalent product here and failed, which is why I ended up with the polyurethane foam. One other contractor I've talked with in the U.S. also used foam, but I neglected to ask him if he chose not to use steel nails for some reason.

Here in California we use Dobies to seperate the rebar from the ground/insulation. Dobies are simple 3" x 3" x 3" concrete cubes with a wire in them. Check out the much snazzier looking rebar spacers they use in Australia. The wall does not appear to have a bond beam at the top, but instead is pretty thick the whole way up.

Insulating the piping has been a major effort on my project. It's not clear in these pictures if this pool's piping is insulated.

Gunite going in:

His pool is in basically the same condition as mine right now. Note the clever combination of bench seat and stairs at the right hand side of the pool. Very nice. The pool looks deeper than it is because the lot slopes up to the left, and the left hand side of the pool is a retaining wall (raised bond beam).

It's a nice looking project, and I'm very curious to see how it turns out. Thanks a lot, Melbourne!

Reynolds number

It looks like one of the problems with the fountain is that I'm pushing slightly too much water through the flow straightener.

At very low velocities, flow through a pipe is laminar.  I wanted laminar flow in the flow straightener because laminar flow has no turbulence which can then break up the output jet.  It turns out that the flow velocity in the pipe has to be incredibly slow, and it turns out that I managed to design my fountain to be right in the transition region between turbulent and laminar flow.

Here is the Engineering Toolbox link on Reynold's numbers.

At full flow, I'm pushing about 180 gallons/minute through 16 of those flow straighteners.  Each has an internal diameter of 15.3 cm, so that the flow rate is 3.85 cm/sec.  Plug that into the handy calculator (the one using kinematic viscosity) and you get a Reynold's number of 5213.  That's turbulent flow.

At the flow tested in January (which worked properly), I was going up about 33 inches instead of 65 inches, so my jet velocity was 71% of full flow now.  Also, the cross section of the jets was .41 inches instead of 0.5 inches as it is now, so that the velocity inside the flow straightener was 48% of what it is now.  Plug 1.84 cm/s into that Reynold's number calculator and I get... 2491.  That's transient flow, but quite close to the 2300 needed for laminar flow.

If this is really the only problem with the fountain, then I ought to be able to slow down the flow enough to get the Reynold's number down to something around 2300, and see laminar flow at the output.  How slow?  To get half as much flow, the jet velocity is halved, and the arc height goes to 1/4 of what it is now, or 16.5 inches.  In fact, at that velocity, I do indeed get laminar flow:

Note that the impact here is on the first step into the hot tub, which is a little lower than the nominal water surface, and the arc is about 20 inches above the nozzle rather than 16.

The jet is well behaved until it gets to the top of the arc, where the bottom of the jet interferes with the top of the jet, and the result is that is spreads out laterally. That lateral spread then turns into an oscillation in the flow until it hits the step.

Anya demonstrates that the jet is 18 inches above the bond beam, or about 20 inches above the nozzle.

At this point the default setting for the fountain is to throttle back to 40 inches throw height, which clears the occupants of the hot tub and isn't too noisy.

If we wanted to get the tall jets to behave properly, it appears we'd need to cut the flow rate approximately in half, which means we'd have to reduce the jet diameter to 0.350 inches instead of 0.500 as it is now (so the finished hole diameter would be 0.440 inches).  That means I'd have to pull the stainless steel nozzles (recall they are epoxied into the PVC heads right now), get new nozzle made (probably $300), and epoxy them back in.  That all sounds possible, and certainly cheap enough, and probably can be done fast enough given that it's going to take 5 weeks to get the tile delivered.

However, there's a good chance I'd just destroy the PVC heads in the process, and there is also a good chance I'd get the nozzles glued back in crooked.  I don't think we're going to try.

We're getting more comfortable with how it looks.

Fountain test

Belle, non?  (1/80 sec exposure)

Non. (1/4000 sec exposure)

Here it is with Martha for a sense of scale:

First, what went right?

• The geometry is right.  In this spreadsheet, I calculated the height of the fountain (69.4 inches, was actually 65.5 inches), and how far it would throw the water, and where the jets would come down into the hot tub.  Although some of the jets land about 5 inches off where I expected, and two jets collide in midair just before they hit the water, the geometry is about as good as can be expected, and fulfills my goals, which were:
  • It should be possible to walk between the rising jets without being hit by them.
  • It should be possible to sit in the hot tub without being hit by the jets.
  • It should be possible for a child to stand in the middle of the hot tub and have the jets come down all around, without actually hitting the child.
• All the jets rise to the same altitude, within about half an inch or less, which means the balanced binary tree distribution system with the shorted end terminals worked.
• The pump-side pressure stack does not overflow.
• The pumps don't cavitate.  They are incredibly quiet.  You cannot hear them unless you walk over to the pump vault and stand on top of it.  Once the lid is installed on the pump vault, I doubt you will hear the pumps even when you are on top of it.

However, the jets are not laminar.  Gloppy blobs of water fall into the water and make a dull roar instead of the quiet sizzle that I had wanted.  There is enough splashing from the jets entering the water that you wouldn't want that a few inches from your face.  The kids love it, of course, because it's loud, fast, and wet, but it's not so great for the adults.

I'm pretty bummed.  What happened?

The individual jets were flow tested in January, and this is what they looked like then:

As you can see, the jets were smooth, and landed smoothly and quietly, back in January.  Now Martha jokes that if we move the back yard table to the farthest corner of the yard, we can still have a nice conversation.

I'm not entirely sure why there is a difference.  Here are possibilities, ranked by my guess of most to least likely.

• In January, the heads had no lateral ports in them.  In this latest trial, there are two ports in each head, connecting each to the heads on either side.  These ports keep the pressure even across all the jets, which makes them shoot to the same altitude.  But these ports may also be causing the water to tumble slightly as it passes the edges, and that turbulence may be causing the breakup that I'm seeing.
• In January, the heads were surrounded by nothing, and so small amounts of water on top of the heads ran down the sides, away from the jets.  Now, the heads sit inside recesses in the gunite.  Each head has a small pool of water in it that terminates at the jet.  The water in this pool greatly disturbs the jet during startup, but it gets cleared in two or three seconds and then I don't think there is any more water recirculating through that pool and into the jet.
• In the January trial, I had an open-topped pressure stack between the pump and the jets.  In the production version, I have a stack after the pump, but it's not quite the same.  In this one, the water from the pumps goes to a Tee.  In one direction, the water heads for the jets, and in the other direction, the water heads for the stack.  It's possible this alternate arrangement works less well.
• This test has a closed air volume right before the jet, which was intended to be an additional flow smoothing device.  The January arrangement used open-topped pressure stacks either right before each flow straightener, or right after the pump, and both worked well.  The closed air volume is known not to work as well (since the pressure changes more with a small surge in water).  Also, since the current arrangement has two capacitors with an inductor between, it's possible that there is oscillating pressure being stored between the two capacitors.
• The nozzle holes are 0.590 inches, rather than the 0.500 inch holes that I tested in January.  This makes the jet diameters about 0.500 inches, which is necessary for all 200 gallons/minute to flow.  As a result of the larger jet and the larger jet velocity, the flow through the flow straightener is perhaps twice as fast as it was in January.  It would be great if this were the problem, since I can reduce the flow later when I have that plumbing finished.
• In January, the pump had air in the lint basket bowl, and the pump could be heard continually injesting air.  Now the pumps have no air in their lint basket bowls.  I would expect this to make things better now, but I thought I'd list it because it is a difference.

I also have two unexpected observations which may be a clue to a solution if I can figure it out:

The ports in the sides of the fountain heads are connected via riser pipes to a plenum that is fed from a pipe that will ordinarily lead to a blocked valve.  This valve is used when the fountain is off to backflush the flow straighteners.  However, that plumbing is not yet finished, and so the pipe currently leads to many other pipes that are currently filled with air.  There is also a hose bib and a pressure gauge connected to those pipes (this is how we did the pressure test).  I have calculated that the static pressure at the top of those fountain heads is about 3 psi above ambient, and so I expected the plenum to be pressurized at 3 psi.

But that's not what the gauge says.  The gauge shows zero pressure (I don't have any gauges that show negative pressures).  If I open the hose bib while the fountain is running, then cover the opening with my finger, I feel a little pull.  It's very feeble, but it's there.  WTF?

The flow in the head is moving at 1.6 inches/second, and I calculate a dynamic pressure of 0.85 Pascals, or 0.00012 psi.  That isn't diddly compared to 3 psi pushing out.

[Update: Mystery retired: it turns out that the pipe connected to the top manifold is capped off right now, and those other pipes are just not connected to the fountain.  I can't explain why I was thinking that there was a small pull of air, but it certainly wasn't measureable.]

The second unexpected thing happened the first time I started up two of the three fountain pumps.  All three pumps are in parallel.  I had difficulty taking the lid off the third pump's lint basket bowl, so I had left that bowl filled with air, and just started the other two (which were properly filled with water).  I expected the first two pumps to push water backwards through the third pump, flushing the air into the intakes of the first two, where it would be blown into the fountain or otherwise ejected from the system.

Nope.  There was no noticeable flow through that third pump.  Later, I pulled that lid off and removed the air.  When I ran just two pumps again, the third pump did have flow going backwards, and in fact the impeller was turning backwards at perhaps half the RPM of the two powered pumps.

It's not clear to me how the air can block a >3 psi pressure drop.  The total drop from the top of the pump to the bottom of any associated piping is perhaps two feet, which would account for a 1 psi drop block, but not 3.

I suspect that the solution to these mysteries, especially the first, will tell me something about the fountain behavior.

Gunite is in

Kathleen is spraying water on the gunite, Anya is directing, while Ava looks on. We're supposed to keep the gunite wet for the next two weeks.

I stayed home for the day to watch the crew shoot the gunite. We used Aqua Gunite (here is their web site), on the recommendation of our consulting engineer Charlie Adams. I found a listing for them here. It's listed as a two-person company, which I suppose would be Jose Aguayo and Sergio Garcia. For a two-person company this place has a lot of assets: at one point I saw three and my neighbor reports five trucks lined up to deliver the sand/cement mix. Those trucks had Aqua Gunite logos and Charlie tells me they cost $260k each. They also had what my friend Wes Grass reports to be the largest air compressor he's even seen (it was all of a large truck). Maybe the company is owned by those two guys.

They got here at 7:30AM and had the gunite going by maybe 8:00AM. That gun was shooting almost continuously until something like 5:45PM, and it took them another 30 minutes after that to finish up. We used almost five truckloads of gunite (our pool is 46 feet by 18 feet, and has a big cover vault at one end). Sergio, the foreman, told me that was 78 to 80 cubic yards of gunite, but I can't see how that's possible:

• The shell surface area is 2015 square feet that average around 8.5 inches thick (53 yards^3).
• We have about 38 feet of internal dam walls that are about a foot thick and average 4 feet tall (5.6 yards^3).
  
• There is maybe 3 cubic yards of gunite in the steps and two pedestals.
• We have a gusset which holds up the diving board that is 2 feet by 2 feet by 6 feet, so that's another yard.
• 10% rebound would be another 6 yards, which is consistent with what I observed getting dumped and hauled away.
• Total: 68 cubic yards.

Those trucks were claimed to hold 15 cubic yards, but they just did not look big enough. Maybe that's the volume of the containers, which they perhaps don't usually fill completely. For comparison, a 10-wheeler holds 10 cubic yards.

The cement and sand is mixed in the truck right before delivery, and the water is only added in the nozzle at the end. As a result, they don't have the usual concrete problem of having to order exactly the right amount of mix. Instead, they have the problem of disposing of "rebound", which is the portion of the stream that does not stick when it hits the wall. Sergio says they usually have 7 to 10% rebound. Aqua Gunite carefully arranges not to have the capability to offhaul the rebound -- they want to dispose of it somewhere on site. We had a nice big hole in which to dump 2 or 3 cubic yards, but after that we piled it up on what used to be our lawn and had some other folks cart it off for recycling the next day. In retrospect it probably would have been a good idea to negotiate this ahead of time with Jose.

It doesn't much matter, we had a fixed-price contract: $13145, $733 of which was for using thicker masonite so that we wouldn't have to strip the forms to make the form edge straight. This last bit is an artifact of our having a bond beam raised 15 inches out of the ground -- the sides have to be straight so that the masons can lay the siding stone properly.

One of the first things Sergio decided when he got here is that we didn't have enough rebar in the cover vault dam wall. The wall is 12 inches thick, and had just a single curtain of #3 rebar on 12 inch centers on the water side, plus four #4 rebar at the top. Sergio added another curtain of #3 rebar on 12 inch centers on the vault side. One nice side effect is that this will make the vault floor even more resistant to cracking from the applied torque should the gravel under the pool settle and leave the pool hanging on the soil under the cover vault.

Here's the top of the gusset that holds up the diving board. You can see the four two-foot bolts that actually go up to the diving board base. In retrospect, I should have had the gusset rebar tied into the vault wall rebar better, as that would help transmit loads between the two.

So now we wait four weeks for the gunite to harden, and shrink, and maybe crack, while we race to get the plumbing, electrical, and solar installations finished, and get the trenches closed up and filled in preparation for the new landscaping. In the meantime, the maintenance crew is keeping the shell wet.

Ready for gunite

We passed our plumbing inspection, so we're ready for gunite. This has been the eighth weekend in a row that I've worked both days on the pool plumbing. Virtually all of that work has been on the hot tub. (Earlier I was working on plumbing too, but I was machining bits and it didn't feel as much like plumbing.)

Picture right is David Kanter, by the way, who was generous enough to come down last weekend and sweat in the 100 degree noontime sun to lay gravel in the trenches around the pool. This is us right before cutting those 3" pipes to make the main drains. Thanks, Dave!

I like this picture because it gives a sense of the scale of this thing. Granted, it will be a smaller hole once 6 to 15 inches of gunite have gone into the sides, and 10 inches has gone into the bottom. But it will still be big enough that, standing on the bottom with no water to buoy you, you will not be able to jump up and touch a string suspended across the waterline. It's significantly deeper than most rooms are tall.

After looking at this thing, the inspector asked me to double the rebar in the hot tub because of all the plumbing. Done in two hours, and the pic is below. [Update, years later: damn good thing the inspector caught this.  The spa dam wall has developed a small circumferential crack. Because the inner layer of gunite has it's own reinforcing, this is not a big problem, but in retrospect I should have inserted rebar that stitched the inside curtain to the outside curtain.]

We tested a fair bit of this hot tub plumbing to 30 psi, and I was amazed that it held. Most of my flexPVC is tested now, and not a single leak.

Unfortunately, the Valterra 4 inch gate valve on the suction side of the fountain pumps leaks. This is an expensive part, and after talking with the manufacturer it seems that it was never going to work right. Finding an alternative is going to be very expensive. If any reader happens to know of a 4 inch valve made of something compatible with ozone (stainless steel, especially 316, and PVC are the big ones) which won't rust and leave stains on my plaster, and which doesn't have a huge flange... please pass along the info. Oh, and it should take 30 psi of internal pressure without leaking. It doesn't have to take 30 psi across the ports when closed, but 3 would be good.

[Update: I've ordered a 4 inch Spears PVC ball valve. It's a very nice valve, very, very easy to turn, but it was crazy expensive: $670. Including the cost of the built-to-fail Valterra gate valve and installation and rip-out of that, this one item has cost $1000. This could have been done more cost-effectively.]

It is now conceivable that we could have the pool open by June 5 (Anya's birthday), but I don't think it's going to happen. Every other aspect of this pool has taken much longer than expected, so I assume that it will be hard to just finish the plumbing over the next four weekends, let alone get the tile, plaster, cover, coping, electrical, solar panels, diving board, rock facing, patio, drainage, lighting, planting, and sprinklers done.

Fountain update: flexPVC limitations

My dad came down today, and we got a lot done.

2.5 of the 3 lower manifolds are now complete, and the fountain plumbing is now good enough for the pool rebar to be installed. This is great news because it means I am nearly released from the critical path and we can go from having one amateur working two days a week to maybe three or four professionals working 5 days a week. I expect a speedup of at least 7 times!

The bottom manifolds are made of flexible PVC pipe. This stuff is made with two different plastic formulations coextruded. The first is rigid white PVC, just like regular pipes are made of, which is formed into a spiral. The seconds is flexible PVC (with Phthalate mixed in for flexibility), which fills the gaps between the coils. This stuff is a little tricky to work with.

The first problem is that the pipe arrives in coils. By the time you get it, the stuff has achieved something of a permanent bend. I was able to take most of this out by unwinding the stuff down the middle of the pool, where it got hot in the sun for a week.

I have not determined a good way to cut the flexPVC. I'm using my miter saw to cut my pipe, because it makes such nice clear burr-free cuts on the regular PVC pipe. On the flexible stuff it leaves a hot, smoking cut with lots of burrs that I clean up with a knife. The Phthalate is particularly annoying, because our chickens love to eat the PVC chips from the saw, and we eat the chicken eggs, and phthalate is bad stuff. So, the chickens are cooped up on days when I'm cutting flexPVC, and I vacuum up everything afterwards.

We're also having difficulty just measuring the stuff. Somehow we're making lot of mistakes where we measure, cut, and then find that it's not the right length. I think the basic issue is that we're trying to measure curved paths with a tape measure.

Joints are a little scary with the flexPVC pipe. I had a professional plumber recommend that we encase every flexible PVC pipe joint in concrete. Now that I've done a bunch, I agree. If there is any bending load on the joint when it's made, the pipe sits in the socket at an angle, and in a few of those joints I can feel that the PVC glue has not completely filled the space between pipe and socket. I made most of the joints with no load while it was curing, and let them sit for at least a day before putting load on them. Those joints I'm quite comfortable with.

Dad points out that if I have a few leakers, the leak rate will be very low due to the concrete barrier and very low pressure in the system (3-6 psi). The plan is to pressure test before gunite, but that is going to be hard to pull off. I'm concerned I'm going to have leaks in the plastic membrane which collects the water, and this will hide any leaks in the piping.

Fountain Progress

Here is the current state of the fountain. I have it installed in the pool, with the central fixture glued in place. The flow straighteners and the first level of distribution to them is in place. In this picture, I'm holding the original prototype for the fountain. It was going to be a piece of cake, I promised. One other note: the inside diameter of the dam wall will be 6 feet 11 inches. The tub looks a little small in this picture. It doesn't seem small in real life, I think the distortion is because I'm slightly in front of the tub and Martha is shooting with a 35mm (wide angle) lens.
Here is my SolidWorks model of the same thing. It's not quite right, in that the rotation of the wooden fixture in the middle is off, and the risers which feed the upper cross pipes are not all in place in the physical object. Ryan and Wes from work stopped by on Saturday to help with the lift. I had built half the fountain in the garage, which was around 250 pounds of stiff, delicate stuff that had to be hauled out to the back yard and levelled. Having an extra pair of critical eyes was very helpful.
Here's the next step (next weekend). I'm going to add the risers for the usual jets that a hot tub has. In this case, there are two kinds: one that comes from the main pool pump, which has enough pressure to pick up bubbles through a venturi, and the other that comes from the fountain pumps, which I don't think will have enough pressure for the venturis (so, no bubbles).
After that, the risers all get tied together at the bottom with a set of three manifolds. The main pool pump drives into the outer one when I want to backflush the flow straighteners. The same pump drives into the center one when I want bubble jets in the spa. The fountain pumps drive into the inner one to whatever extent is necessary to trim the fountains to the right amount of flow.
Finally, before I can do any of the plumbing for the spa drains and major hookups, the fixture has to be sawed out. Here is what it will look like then.

The guys at work are calling it my nuclear reactor.

Thanks, Ryan and Wes!