poolnerd

A near-by neighbor of mine has a swimming pool with an attached spa. His system is set to come on at 11:00 pm and circulate for three hours. I know this because I can hear the system come on and run. It wakes me up almost every night. It’s LOUD.

Know why it’s so loud? The main reason is that the pipes feeding the pump are too small. Since it’s a pool/spa combination, there’s a 2 hp pump running everything: pool circulation, spa jets. Nothing wrong with that, though; it’s pretty common around here. It’s a fairly basic (cheap) way of setting up the plumbing systems, or what us pool nerds call “hydraulics.”

Also common around here, and in many parts of Southern California, is the practice of using 2-inch lines for most pipe runs: skimmer line and pool return, spa suction and spa return, and often a 1½-inch line for a suction-side pool cleaner.

That’s the set-up my neighbor has… unfortunately.

But if you’re using these line sizes and a 2 hp pump, your pump will howl… as my neighbor’s does … unfortunately. It’s basically starved for water. Since the pipes are too small, the pump is working too hard. If you open up the pipe sizes, the pump gets more water, and it will run much more quietly.

Oversized Pool Pipes for a Happier You

For pools up to seven or eight hundred square feet in surface area, using one skimmer should be sufficient. Since that is the majority of pools out there, we’ll use that as an example (if you plan on building a larger pool, you may consider two skimmers and perhaps multiple pumps to drive spa jets and water features).

Most skimmers on the market have 2-inch pipe connections and are rated at 55 gallons per minute (gpm). One company, Waterway Plastics, makes a skimmer rated at 75 gpm. It has a 2½-inch pipe connection. It costs a couple of bucks more (actually $3.76 plus tax, but your mileage my vary), but I’d recommend using this skimmer, and running 2½-inch pipe all the way to the equipment pad. The extra capacity is well worth it.

It’s also a good idea to run a separate, dedicated line for a suction-side pool cleaner, like a Kreepy Krauly or Barracuda. Some pool builders use a 1½-inch line for this, but a 2-inch pipe only costs a few dollars more, and can supply more water to the pump, ensuring that it will run more quietly. Just make sure it gets reduced down to a 1½-inch female-thread fitting at the finished pool wall: that’s what most pool cleaners connect to.

Suction lines are only part of the equation, though; return lines are the other. For filtered water returning to the pool, it’s a good idea to use the same size pipe as for your main run, in this case, the 2½-inch skimmer suction line. That line runs from the equipment pad back to the pool. Near the pool, it usually steps down in size as it’s distributed to the pool return inlets. Those are the places where water comes back into the pool. You’ve probably seen or felt them before. Kids love to stick their fingers in them, delighting in fighting the push of the water pressure from the pump. The number and layout of the return inlets depends on the size and configuration of your pool. Your plumbing contractor can help with this. It is a good idea to have at least one inlet set fairly low, perhaps at a depth of three feet, or even greater, especially if you’ll be heating the pool. This helps mix the water better, preventing thermal stratification.

Big Pipes for a More Relaxing Spa

Spa plumbing is a little more technical. Hydrotherapy jets have certain minimum flow requirements (in gpm) and minimum operating pressures (measured in pounds per square inch, or psi) required for mixing air into the water flow. If these two criteria aren’t met, the jets won’t draft air properly, resulting in a lack of bubbles in your spa.

Also, it’s nice to have jets that are of equal strength. For this, you need to have a looped manifold that all of the jets come off: the return line runs to a tee, which feeds a complete loop, a circle. This means that all jets will get equal flow. Another trick is to ensure that each jet has the same number and type of fitting between the jet body and the manifold.

On my jobs, for example, I run a three inch return line to a 3-inch tee. It feeds into the bottom of the “T”, and the sides of the tee have 3×2-inch bushings, leading to a continuous 2-inch manifold with seven jets. Coming off the manifold, we reduce to one-inch pipe and fittings: two 1-inch 90-degree elbows lead to the jet body. All of this ensures equal flow and pressure to all of the jets, which means that they’ll all feel the same to someone enjoying the spa.

Again, your plumbing contractor can help you select the proper number of jets, and where they can and can’t be located.

For a quieter pump, you should use at least 2½-inch pipe for the spa suction line. Three-inch is even better, and actually provides for slightly more flow, which means you might be able to have one additional jet. Again, use the same size pipe for the return pipe run as you did for the suction line.

Safety and Suction Lines: IMPORTANT!

While we’re on the subject of suction lines, let’s cover one more detail. It relates to safety. It’s required that the all suction lines, pool or spa, be split: connected to minimum of two drain outlets of the same size as the main supply line, separated by at least three feet or on different planes. This is meant to help prevent suction entrapment, a situation where someone can be pulled into or onto a drain and trapped. The drain covers must be the right type, too: anti-vortex or safety covers, which can be removed only with tools. The plastering contractor usually provides the drain covers, but it’s a good idea to check that the ones he brings out are suitable.

Filter Size

Besides just properly sized pipes, you also need a filter that won’t impede the flow. If you cheap-out on the filter, your pump will still howl.

All filters have flow ratings; just pick one that exceeds your maximum anticipated flow. Cartridge filters are usually rated at about one gpm of flow for every square foot of surface area (a 100 sq. ft. filter is often rated at 100 gpm). DE filters are rated at 2 to 2½ gpm per sq. ft. of surface area ( 60 sq. ft. DE filter is usually rated either at 120 or 150 gpm). A bigger filter also keeps the pool cleaner, and means it can hold more debris (which in turn means you clean it less often). This is probably of some importance to you, too.

There are three main types of filters: sand, cartridge and diatomaceous earth (DE). Each has its advantages and disadvantages, and some are more prevalent in some parts of the country. Read more about filters here.

One additional aside about DE filters: try to get one with a backwash valve, which is used for easier cleaning of the filter. But be careful about which backwash valve you select. Some types can add significantly to the total head loss (the amount of resistance) of the system. High-flow piston-type valves are available from some manufacturers, as are bottom-mounted rotary backwash valves.

Other Nifty Benefits

So, let’s say you’ve chosen (perhaps with the help of some professionals) the proper pipe sizes and plumbing layouts. Now your pump should run more quietly than my neighbor’s. But what else do you gain?

Since your pool will have a properly designed hydraulic system:

• Your system will run more quietly. Your neighbors should appreciate this; I sure would.
• You won’t need to run your pump as much to filter the pool. More gpm’s mean less filtration time to filter the same amount of water. This will, of course, save money on your energy bills.
• You will have lower long term repair costs. Since your pump won’t be working so hard, your system will require fewer repairs.
• Your pool and/or spa will be safer. Proper drain configuration, the right covers, and operating at the recommended water velocities all make your pool as safe as it can be.
• If you have a spa attached to the pool, you will be able to install an additional jet or two. More gpm’s mean more jets, and that makes a more relaxing spa.

There is much more to this subject of hydraulics than we’ve covered here, though: figuring out total head loss for the system, keeping line velocities below 6 feet per second, figuring out a system curve for a particular plumbing layout and matching the appropriate pump to it, and so on. But what we’ve covered here is a good start (actually, it’s more than most pool salespeople — and even some contractors — know).

This entry was posted on Friday, November 24th, 2006 at 3:30 pm and is filed under Uncategorized, Constuction, Design, For Homeowners, For Contractors. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.